Raw pasta is a convenient environment for various biochemical and microbiological processes. To prevent the development of these processes, products are preserved by drying to a moisture content of no more than 13%.

Drying pasta is the longest stage in the production process. The modes of its implementation largely depend on such indicators of the quality of finished products as strength, vitreousness in fracture, acidity. Intensive drying can lead to cracking of the products; excessively prolonged drying at the first stage of moisture removal, - to souring, swelling of products; when drying in a layer - to the formation of ingots, deformation of products.

Drying is completed when the products reach a moisture content of 13.5-14%, so that after cooling, before packaging, their moisture content is no more than 13%.

Convective drying method

The convective drying method is based on heat and moisture exchange between the material to be dried and the heated drying air that blows over the products. The drying process consists in supplying moisture inside the product to its surface, converting moisture into steam and removing steam from the surface of the product. In this case, the drying air performs the following main functions:

a) gives the material the energy (heat) necessary to convert water into steam;

b) absorbs vapor evaporating from the surface of products;

c) removes evaporated steam from the product.

The main parameters of the drying air that determine the rate of drying of products are temperature, relative humidity and speed of movement. The higher the temperature of the drying air, the more intensive is the evaporation of moisture from the surface of the products; the lower the relative humidity of the air, i.e. the more “drier” it is, the more intensively it will absorb evaporating moisture, and the higher the speed of air movement over the products, the faster the evaporated moisture will be removed from them.

The movement of moisture from the inner layers of the material to the outer ones occurs under the influence of the moisture gradient, i.e. differences in the moisture content of the layers, resulting from the evaporation of moisture from the surface of the material and the drying of the outer layers. The moisture gradient is directed towards the center of the items to be dried, i.e. in the opposite direction to the movement of moisture. Its value is the greater, the more intensively the drying of the outer layers takes place. The phenomenon of moisture movement under the influence of a moisture gradient is called moisture conductivity, or concentration diffusion.

When drying pasta with air with certain parameters, the moisture content of the dried products will gradually decrease to a certain value, called the equilibrium moisture content. Drying air with certain parameter values ​​(temperature, humidity) corresponds to a certain equilibrium moisture content of the products, which will not decrease, no matter how much the product is blown with this air.

For the correct selection of the drying mode, it is very important to know the values ​​of the equilibrium moisture content of pasta, which are determined from the curves of the equilibrium moisture content.

Changing the properties of pasta during drying

A feature of drying pasta is the change in their structural and mechanical properties and sizes. During drying, the moisture content of the product decreases from 29-30% to 13-14%, while there is a gradual reduction in linear and volumetric dimensions, shrinkage of products is 6-8%.

Raw products for drying are a plastic material and retain their plastic properties up to about 20% moisture. With a decrease in humidity from about 20 to 16%, they gradually lose the properties of a plastic material and acquire properties characteristic of an elastic material. With such humidity, pasta is an elastoplastic body.

Starting from about 16% moisture, the pasta becomes a firm elastic body and retains its properties until the end of drying.

With gentle drying modes, i.e. slow drying with air with a low drying capacity, the difference in humidity between the outer and inner layers is small, since moisture from the more humid inner layers has time to move to the dried outer layers. All layers of products are reduced approximately evenly. The drying capacity of air is characterized by the amount of moisture that can absorb 1 kg of air until it is completely saturated, i.e. up to 100% humidity.

With severe drying modes, i.e. intensive drying with air with a high drying capacity, the difference in humidity between the outer and central layers reaches a significant value due to the fact that moisture from the inner layers does not have time to move to the outer ones. The drier outer layers tend to shorten their length, which is hindered by the wetter inner layers. At the boundary of the layers, stresses arise, called internal shear stresses, the magnitude of which is the more significant, the more intensively moisture is removed from the surface of the products and the greater the difference in moisture (moisture gradient).

While the dried pasta retains its plastic properties, the resulting internal shear stresses are absorbed, i.e. products change their shape under the influence of stresses, without collapsing. When a product acquires the properties of an elastic body, the resulting internal shear stresses, if they exceed the maximum permissible, critical values, lead to the destruction of products - the appearance of microcracks, which, ultimately, can turn products into crumbs.

Thus, pasta can be dried under severe conditions, without fear of cracks in them, up to a moisture content of 20%. When the product reaches this moisture content, in order to avoid cracking, it is necessary to dry it under mild conditions, slowly removing moisture. You should be especially careful when removing moisture in the last stages of drying when the products reach a moisture content of 16% and below. This conclusion finds practical application when drying products in dryers of modern production lines, in which the drying process is divided into two stages - preliminary and final drying.

Drying modes of products

The term drying mode is understood as a set of parameters of the drying air (temperature, relative humidity, air velocity) and the duration of drying. The optimal mode for drying a certain type of pasta is considered to be such a mode in which products of normal quality are obtained with the shortest drying time and energy consumption.

Currently, the following modes of convective drying of pasta are used:

traditional low-temperature ones with a drying air temperature up to 60 С;

high-temperature with a drying air temperature from 70 to 90 С;

ultra-high temperature with a temperature of more than 90 С.

Low-temperature modes are most common for drying pasta: with a constant drying capacity, with a variable drying capacity, three-stage.

Drying with constant air drying capacity. Drying of products is carried out in cabinet-type non-calorifier dryers of the VVP, "Diffuser" and 2TSAGI-700 types.

Cassettes filled with raw pasta are placed either on trolleys, which are taken to the drying department, where the cassettes are installed on the shelves of drying machines, or in trolley cabinets, which are placed close to the drying cabinets.

Cassettes on the shelves of dryers or in trolleys are stacked in several rows in width and height.

Cabinet dryers are equipped with ventilation units. Drying of pasta is carried out by blowing air through the pasta tubes lying in the cassettes. Air from the workshop is used to dry the pasta. For uniform drying, periodically (after 1 hour), the direction of air movement is reversed, switching the electric motor to work in the opposite direction.

In the drying shop, the air parameters are maintained at a constant level by means of supply and exhaust ventilation, i.e. air has a constant drying capacity, namely: a temperature of about 30 ° C and a relative humidity of 65-70%. The air in the workshop is heated either by a battery of heating radiators, or by a heater, through which fresh air is pumped into the workshop instead of the humidified exhaust air sucked from the workshop. Drying time is about 24 hours.

When drying in tray cassettes, the pasta is blown with air from the inner and outer surfaces of the tubes. Due to the uneven contact of the pasta with each other, there is an uneven removal of moisture from their surface, and therefore, uneven shrinkage of the products. This leads to the curvature of products during drying, which significantly reduces their quality, increases the consumption of containers for packaging. The contact of the tubes in the cassette and the impossibility of quick moisture removal at the initial stage of drying lead to sticking of products and the formation of ingots.

The disadvantages of this drying method are also the high costs of manual labor and the discomfort of the room (high temperature and humidity), in which the drying is carried out.

Three-stage drying mode. The mode consists of three stages (preliminary drying, tempering, final drying). Hanging drying of long items. Drying of long pasta (noodles and noodles of various types, straws and special pasta) by hanging method is carried out in tunnel dryers (preliminary and final) of automated production lines B6-LMG, B6-LMV, LMB and in the lines of Braibanti. Items hung on bastuns slowly move in the tunnels of dryers, blowing air from top to bottom.

The purpose of pre-drying is to quickly remove moisture from raw pasta at the stage when they have plastic properties. The main purpose of this stage is to reduce the overall drying time of the pasta. A rapid decrease in the moisture content of products prevents the development of various microbiological and biochemical processes, primarily souring, swelling and darkening of pasta.

The parameters of the drying air in the preliminary dryer, depending on the products, are: temperature 35-45 ° С, relative air humidity 65-75%. The moisture content of the semi-finished product at the stage of preliminary drying is reduced to 20%. The pre-drying time on these lines is about 3 hours.

The final dryers are divided in length into drying and tempering zones.

In the zones of heating (the second stage), the relative humidity of the air is close to saturation (to 100%), therefore there is no evaporation of moisture from the surface of the products. In these zones, the temperature and humidity of the product are equalized in all inner layers: the slow migration of moisture inside the products to the surface, from where the moisture was removed while the products were in the previous drying zone. In this case, the internal shear stresses resulting from this removal are resolved.

In the drying zones (third stage), fans and air heaters are installed, with the help of which the drying air heats up and blows the products hanging on the bastuns. The air temperature in the final drying zones is, as in the preliminary dryer, 35-45 ° C, and the relative humidity is slightly higher - 70-85%.

Bastuns with products, alternately cross the drying zone and the heating zone. Thus, moisture is removed from the product in steps, i.e. drying periods alternate with heating periods. As a result of the so-called pulsating drying mode, durable products with a glassy break are obtained.

The duration of the final drying of products depends on the assortment and on average ranges from 11 to 15 hours. Products leaving the final dryer chamber, having a moisture content of 13.5-14%, are sent to the stabilization chamber for cooling.

Drying of short products in dryers of automatic production lines. Drying of short (short-cut and stamped) products in dryers (preliminary and final) of automatic production lines is carried out in three stages. The stages of preliminary and final drying are preceded by a stage of primary drying. It is carried out in installations (trabatto), where raw products perform "jumping" movements, blowing for 2-3 minutes. hot air. A dried layer is formed on the surface of the products, which prevents them from sticking during subsequent drying "in a layer" on the belts of conveyor dryers.

Drying with variable air capacity. Drying of short products in steam conveyor dryers. Raw products are distributed by the spreader onto the belt of the upper conveyor of the dryer, slowly move in the opposite direction, poured onto the belt of the next conveyor, and so on - to the lower conveyor, which are fed to unloading.

The layers of products lying on the conveyor belts are permeated with drying air, which is sucked in at the bottom and thrown out at the top of the dryer. Fresh air is heated by the lower heater to a temperature of 50-60 ° C and a relative humidity of 15-20%. Then the heated drying air passes through the layer of products lying on the lower conveyor, gives them part of the heat and is humidified. Having passed through the second heater, the air heats up again to approximately the same temperature, passes the layer of products lying on the belt of the second conveyor, and so on - to the upper conveyor. The parameters of the exhaust drying air at the outlet of the dryer are approximately as follows: temperature 40-50 ° C, relative humidity 50-60%. This drying mode is called a mode with an increasing drying ability of air: as the product dries, it is blown with drier air.

The drying time of products (up to a moisture content of 13.5-14%) is, depending on the assortment, from 30 (for noodles and soup fillings) to 90 minutes (for large figured products).

The use of such severe drying regimes often leads to the formation of cracks on the surface of the dried products, especially tubular (feathers, horns) and curly (shells, etc.). The advantages of this mode: high productivity of these dryers with small overall dimensions, as well as the relative ease of maintenance and reliability in operation.

High temperature drying... This mode, in comparison with the traditional one, allows you to reduce energy costs and reduce production areas per unit of produced products, reduce the drying time by an average of 40-50% and, with correctly selected drying modes, improve the quality of pasta (color and cooking properties) and their microbiological state.

High-temperature drying can be carried out in conventional dryers of production lines, while either increasing the productivity of the line by including more powerful presses and increasing the speed of movement of the conveyors of the dryers, or reducing the length of the dryers of the line while maintaining its productivity.

When developing modes for high-temperature drying of pasta, it is necessary to proceed from the following basic prerequisites:

the drying process should be carried out in two main stages: preliminary and final drying;

the temperature of the drying air should be (at one of the stages) within the range of 60-90 ° C. The use of such an interval is due to the fact that 60 ° C is the minimum limit for complete pasteurization of pasta, and 90 ° C is the temperature at which the Maillard melanoidin formation reaction is likely to occur (non-enzymatic darkening of the product);

drying of products should be carried out at high relative humidity in order to avoid excessive removal of moisture from the surface layers of products and the occurrence of dangerous shear stresses between the inner layers of products, which can lead to cracking of the product, turning it into scrap.

Ultra high temperature drying. At present, all the leading companies in the industry "Pavan", "Buehler", "Bassano" produce lines for the production of short pasta with an ultra-high-temperature drying mode. These modes are characterized by the use of drying air with a temperature of more than 90 С and a relative humidity of about 90%, drying in 3 stages. The advantages of ultra-high-temperature drying modes are: reduction of the drying process by accelerating mass transfer; improving the microbiological state of products and sanitary and hygienic conditions of production; improving the quality, cooking properties of products, which is especially important when processing soft wheat flour; reduction of energy consumption by 10-15% and reduction of production space per unit of production.

Drying with preliminary heat treatment of raw products... Heat treatment of products before drying can significantly reduce the process of their dehydration, since it will allow the use of severe drying regimes without fear of cracks. This is due to thermal denaturation of proteins and partial gelatinization of starch, which leads to a decrease in the binding energy of these components with moisture.

Nazarov proposed a method for processing raw long pasta with a steam-air mixture with a temperature of 95-98 ° C and a relative humidity of 95% for 2 minutes, and short-cut products with dry steam with a temperature of 120-180 ° C for 30 seconds, followed by drying the product under severe conditions.

Cooling of products

Pasta products leaving the dryer usually have an elevated temperature equal to that of the drying air. It must be cooled to the temperature of the packing compartment before packing. With slow cooling, the products stabilize: the moisture is finally leveled out over the entire thickness of the products, internal shear stresses remaining after drying are absorbed, as well as a slight decrease in the mass of cooling products due to the evaporation of 0.5-1% moisture from them.

The minimum stabilization time is 4 hours, while the products are washed with air with a temperature of 25-30 ° C and a relative humidity of 60-65%.

Rapid cooling of dried products by intensive blowing in coolers of various designs or cooling them on belt conveyors when feeding them to packaging is undesirable. The dried products in a short time (about 5 minutes) manage to cool to the workshop temperature and do not subsequently dry out after packing, however, in a short period of time, the internal shear stresses not only do not have time to disappear, but also increase, and if the products have been subjected to excessively intensive drying , cracking and crumbling can occur after packaging. In modern automated production lines, stabilization chambers simultaneously act as accumulators: they accumulate products produced during the night shift, which allows organizing the packaging of products only during the day and evening shifts.

Basic methods of drying pasta

Methods for intensifying the drying of pasta

Biochemical changes in starch and protein of pasta and their technological characteristics during heat treatment and drying

Changes in the structural and mechanical properties of pasta subjected to hygrothermal treatment

Mass transfer characteristics and equilibrium critical moisture content of pasta

Installation for drying pasta using new technology and justification of the feasibility of introducing a new drying method

INTRODUCTION

Pasta can be stored for a long time due to low humidity. Drying them is an energy-consuming and time-consuming process from all technological stages of pasta production. Recently, much attention has been paid to the preliminary preparation of the drying object for dehydration. The purpose of this preparation is to reduce the binding energy of moisture with the material and change its thermophysical characteristics, which provide the possibility of using "hard" drying modes without compromising the quality of the product being dried.

BASIC PASTA DRYING METHODS

Convection drying is mainly used in the pasta industry. Various types of drying installations have been developed - from closed chambers to modern drying, tunnel, continuously operating units, equipped with systems for automatic regulation of the parameters of the drying mode. However, even with a high degree of mechanization and automation of these installations, the drying process of products remains long. There are many studies devoted to the problem of intensifying this process by increasing the drying capacity of air; application of new methods of drying; thermo-radiation, radiation-convective, sublimation, etc.

Drying modes used in the pasta industry are diverse. When choosing the optimal drying mode, it is necessary to take into account the technological properties of the pasta dough.

It is known that mainly two types of modes are used for convective drying: continuous and pulsating.

Continuous drying with constant drying capacity of air is simple in terms of regulating air parameters and the process as a whole. The air parameters in this drying mode remain constant throughout the dehydration process.

The main disadvantage of the continuous mode is that drying is carried out with a high drying capacity of air. This mode can only be used for products that are resistant to deformation: soup fillings and powdered products. Drying takes place in a shorter time than long-tube ones, their sizes are smaller, they are better amenable to all-round blowing with air due to spilling.

Long-tube products are dried in a three-stage or pulsed mode. The latter is conventionally divided into the following stages. The first stage is preliminary drying. Its purpose is to stabilize the shape of the products, to prevent freezing, mold and stretching. "Drying" "lasts from 30 minutes to 2 hours and proceeds under relatively" hard "modes during which 1/3 to half of the moisture is removed from the amount that should be removed from the pasta during drying.

Such intensive dehydration is possible only in the first stage of drying, when the pasta dough is plastic and there is no risk of cracking. Further conducting the process under the "hard" mode is impossible, since this will lead to cracking of the products, the resulting large moisture gradient and increased stresses cannot be reduced, since the pasta dough has acquired the properties of an elastic body.

In order to avoid cracking, the second stage is carried out - heating. By increasing the relative humidity of the air, "softening the crust" is achieved due to the moistening of the surface layer, as a result of which the moisture gradient decreases and the resulting stresses are absorbed. This process is best carried out at relatively high temperatures and relative humidity, at which the rate of diffusion of moisture increases, and evaporation of moisture from the surface decreases. Under these conditions, the duration of the heating is reduced.

The third stage - final drying - is carried out under a "soft" mode so that the shear stresses do not exceed the limiting value, since the products are in a state of elastic deformation. In this case, the rate of evaporation of moisture from the surface should be commensurate with the rate of its supply from the inner layers to the upper layer. At this stage, drying can be alternated with heating.

Slow cooling of the product after drying is of great importance so that the moisture gradient is minimal by the time of packaging. With sharp cooling, cracks may form due to insufficient leveling of the moisture content in the layers of the product.

THEM. Savina investigated a three-stage drying mode for short-cut products. It has been found that the total drying time is greatly influenced by the amount of moisture removed during the pre-drying period. A three-stage drying regime was compared with continuous drying at constant air parameters (t = 60 ° С; φ = 70%; V = 0.9 m / s). In both cases, a good product quality was obtained, however, the drying time in a three-stage mode was 20-25% shorter.

IT Taran proposed a 5-stage mode of drying long-tube pasta: preliminary drying; short-term (deep) sedation; re-drying; long-term (superficial) heating and additional drying.

The use of a multi-stage mode has significantly reduced the duration of the drying process to 10-12 hours.

In the pasta laboratory of VNIIHP, work was carried out to study the drying of pasta in rotating cylindrical cassettes according to the method of the French company Bassane .

The possibility of obtaining straight tubular pasta has been proved and it has been established that the cylindrical cassette should have a ratio D / L = 0.47, the end walls should be solid, smooth, without perforations. Products with a moisture content of no more than 29% should be placed in the cassette. ; fill the volume of the cassette with raw products by 62-65%. The dependence of the speed of blowing pasta with an air flow on the live section of the cassette at different frequency of its swing is found.

On the basis of experimental data, the most optimal value of the live section area of ​​the shell for the cassette is revealed - 45%.

It is recommended that preliminary drying be carried out with a drying agent (air temperature 50 ° C and relative humidity 65%) at a speed of 5 m / s e at a cassette swing amplitude of 140 ° C and a swing frequency of 15-12 swings per minute. Drying time 1.5 hours, final moisture content of the semi-finished product - 22%.

After preliminary drying, before starting the final drying, the products must be heated for 60 minutes at an air temperature of 47 ° C, a humidity of 88-94% and a cassette rotation frequency of 2 rpm.

Final drying must be carried out with air with the following parameters: temperature - 50 ° С, relative humidity - 80%, air flow speed - 5 m / s. The swing amplitude of the cassette is 180 ° C, the swing frequency is 15 swings per minute, the duration of swing and blowing is 20 minutes; sedimentation should be carried out for 40 minutes at an air temperature of 47 ° C, a relative humidity of 88-94%, a cassette rotation frequency of 2 rpm. Then the cycle repeats. The total drying time for pasta is 17-18 hours.

At present, the thermo-radiation method of energy supply is used in various industries, in which the intensification of the drying process is achieved through the use of short-wave infrared radiation.

The use of infrared radiation for drying pasta was first studied by A.S. Ginzburg, I. Kh. Melnikova, N. A. Lukyanova, I. M. Savina, and others.

It is noted that due to the peculiarities of moisture movement under the influence of infrared rays, a very rapid dehydration of the surface layer is observed due to the appearance of a significant temperature difference inside the material. As a result of a sharp decrease in humidity on the surface, uneven shrinkage of adjacent layers occurs, which causes cracking of the material. As a consequence, continuous irradiation cannot be used when drying pasta and pasta. A combined thermo-radiation-convective drying method is proposed, in which there is a combination of periodic irradiation of the dried material with convective drying.

For ordinary pasta (7 x 4.5 mm in diameter) made from grade I flour, the following drying mode is recommended:

Medium temperature (t С), ° С ......................................... .................................................. 37

Drying air relative humidity,% ............................................ ...... 70

Air velocity with a layer of pasta, m / s ........................................ ... 2.6

Irradiation generator temperature (tg en), ° С ....................................... ..................100

The ratio of the duration of irradiation and bedding (;), sec ... ... 5: 100

Distance from pasta to emitters (two-sided irradiation), mm ............... 40

Drying time (), hour ……………………………… ..................... 2.6

The experiments of F. Staff (USA) showed that when using infrared radiation, the drying time for short-cut pasta made from high-protein wheat and soy flour is significantly reduced. In this case, the products acquire a brown tint.

In the pasta laboratory of VNIIHP (formerly TsNILMap), work was carried out to study the process of radiation drying of tubular pasta in suspended states. For this, panel-type emitters made in the form of cast iron plates with spirals embedded in them were installed parallel to the pasta strands. The temperature of the radiation generators was 150 ° C; the distance from the surface of the emitter to the product is 170 mm, the duration of irradiation is more than 3 minutes.

For pasta type "Straw" (diameter 8 mm) from flour of the 1st grade (from durum wheat), the best results for combined thermo-radiation-convective drying were obtained under the following modes:

preliminary thermo-radiation-convective drying, consisting of three cycles; in each cycle, irradiation at t = 1b0 ° C, carried out for 3 minutes, alternates with convective drying for 2 hours with the following parameters: t = 32 - 35 ° C; φ = 85%; V = 0.5 m / s, while 7.5% of moisture is removed;

staged convective drying with increasing air drying capacity:

t = 32-35 ° C; φ = 85%; V = 0.5 m / s to W = 19-19.5%

t = 32-35 ° C; φ = 75-80%; V = 0.5 m / s to W = 15%

t = 32-35 ° C; φ = 67-71%; V = 0.5 m / s to W = 13%

The total drying time is 9.5 hours, which is 8.5 hours less than convective drying without irradiation. The effectiveness of irradiation is evidenced by the fact that basically the duration of the process is reduced due to the initial "under drying" (from 29 to 22%), in this zone the drying time is reduced by 5 hours, that is, more than 50% of the total duration of the entire process ... It is characteristic that after preliminary irradiation the drying process proceeds more intensively; it is obvious that the drying regime may be more stringent than usual,

G. Hummel (England) notes that the use of infrared radiation is also possible for drying short-cut products. However, the use of lamps as generators increases the overall dimensions of the installation.

With a combined drying method, the process duration can be reduced to 3 hours, however, the product quality deteriorates, and reducing the drying process duration to 1 hour causes a sharp deterioration in product quality.

Carasoni Laszlo and Harchittau Emmil (Italy) have investigated the possibility of using infrared radiation for drying pasta. In this case, panels were used with a straight distance of the product to the generator 80-100 mm; intermittent drying mode; irradiation 5-30 sec, staying 40 sec. During this period, the dough was cooled with air at room temperature. In this way, drying was carried out to equilibrium moisture content. However, it was not possible to obtain products without cracks. The efficiency of the drying unit was in the range of 4-6%. It has been established that all the work carried out to intensify the drying process can be combined in one direction: the duration of dehydration is regulated by the drying ability of air or the use of new methods of energy supply, while the "water-holding capacity" of the drying object (pasta) remains unchanged.

A decrease in the "water-holding capacity" of raw pasta is possible with a change in their specific, physicochemical properties. The essence of these changes lies in the fact that the pretreatment of the object reduces the binding energy of moisture with the constituent components of the dough. In this way, the products are prepared for the dehydration process.

Recently, the literature has highlighted the issue of finding a method for preliminary processing of the drying object, which allows to reduce the binding energy of moisture with the material. However, an effective method for reducing the binding energy of moisture with dry matter can be considered one that would allow, along with a reduction in drying time, to obtain a finished product that meets all the requirements of the standard. In this regard, it became necessary to find a method for pretreatment of pasta, which would make it possible to obtain products of good quality.

METHODS FOR INTENSIFICATION OF PASTA DRYING

In Switzerland, hydrothermal treatment is complemented by the subsequent freezing of products at a temperature of minus 2b ° C for 15 - 25 minutes.

In the USA, it is proposed to use dry steam heat treatment at a temperature of 101-180 ° C, previously "dried" products with an infrared energy supply for 5-30 seconds.

In France, to speed up drying, raw pasta after pressing is boiled and then kept in ethyl alcohol, which gradually displaces moisture from them; after the final product is quickly dried, and the alcohol is regenerated.

A.S. Ginzburg and V.I. Syroedov, N.I. Nazarov is recommended to use surface-active substances (surfactants), for example, ethyl alcohol, hexane or toluene, which have a low surface tension coefficient, in order to reduce the binding energy of moisture with the material and to intensify the internal moisture transfer.

At MTIPP, studies were carried out to check the following types of heat treatment of pasta: hydrothermal with washing the surface of the products with cold (t = 15 ° C) or hot water (t = 100 ° C) and without washing, followed by freezing and without freezing, as well as hygrothermal treatment carried out according to the same options.

The data show that all types of heat pretreatment of pasta significantly reduce the overall drying time. Thus, the drying of pasta with standard moisture content after hydrothermal treatment with washing in cold water for 5 min and followed by freezing at a temperature of minus 25 ° C for 25 min was 177 min. The parameters of the drying agent were as follows: temperature 90 ° C , relative humidity 30%. Loss of dry substances during cooking, increase in volume, color and structure in the fracture met the requirements of GOST. However, the disadvantage of these methods is that the products stick together. To eliminate adhesion, the products were washed with cold and hot water, frozen and processed in a vibration field. Nevertheless, this all turned out to be ineffective. At the same time, hygrothermal treatment in cassettes, in comparison with hydrothermal treatment, significantly reduces the drying time of pasta. Thus, the duration of drying hygrothermally processed and frozen pasta was 115 minutes, and without freezing, 90 minutes. At the same time, such indicators of the quality of ready-made materials such as the loss of dry substances in the cooking water, an increase in volume were within the requirements of GOST. However, partial adhesion of the products was still observed.

Analysis of the above data made it possible to draw a conclusion about the advantage of hygrothermal treatment over hydrothermal treatment.

Drying of pasta, subjected to hygrothermal treatment in a suspended state on bastuns, with the parameters of the drying unit φ = 80%; t = 60 ° C; V = 1 m / s, allowed to completely avoid sticking of products, the quality of which met all the requirements of GOST. Hygrothermal treatment was carried out at a constant initial moisture content of the products. Steam parameters did not change either. The influence of the duration (1-5 min) of hygrothermal treatment with an interval of 1 min on the drying process and the quality of products has been studied. It was found that hygrothermal treatment of products has a significant effect on the drying process.

In fig. 1 shows the curves of drying pasta with hygrothermal treatment (τ thus) lasting 2 and 5 minutes and without it. The drying process was carried out at "hard" constant parameters of the drying agent. The use of "hard" mode reduces the time of dehydration of products not subjected to hygrothermal treatment from 18-24 hours to 13.6 hours. It should be noted that in industrial conditions, drying is carried out at softer modes. However, with a "hard" drying mode, the outer layers of the products dry out much faster than the inner ones due to the appearance of large moisture gradients and cracking of the pasta is observed both during drying and during storage.

Fig. 1. Drying curves for pasta:

1 - without hygrothermal treatment; 2, 3 - with hygrothermal treatment for 5 and 2 minutes, respectively.

Hygrothermal treatment of products before drying significantly reduces the dehydration process, since it allows the use of "hard" drying modes without fear of cracks. In this case, two interrelated processes take place: thermal denaturation of proteins and modification of starch. The latter, under conditions of moisture deficiency, does not cross the border of the first row of gelatinization. Denaturation of proteins leads to a decrease in the binding energy of moisture with the proteins of the dough and to the strengthening of the structure of the latter. Thus, the tensile strength of products not treated with heat is 320 g, and those processed - 790 g.

Pre-heat-treated pasta did not undergo cracking during storage for 6 months or more. The drying curves shown in Fig. 1 show that the initial moisture content of products without treatment and after it differs sharply. So, pasta with hygrothermal treatment has W = 54.6%, and without it - 47.5%. The first critical humidity (W) is also significantly different: in the first case it is equal to 34%, in the second - 30%.

However, the moisture removal in the first period of drying in pasta after hygrothermal treatment is greater than that of products without it. In heat-treated pasta, it is 20.6%, and in untreated pasta - 17.5%. It should also be noted that the duration of the first drying period in the first case is shorter (55 min) than in the second (125 min).

The second drying period is significantly increased in the case of drying the pasta without heat treatment (690 min versus 480 min). With a given duration of hygrothermal treatment, the equilibrium moisture content of pasta changes slightly (with hygrothermal treatment W = 13%, without it -14%); at the same time, the relative humidity of the air is 80%, the temperature is 60 ° C, the speed is 1.0 m / sec.

Figure 2 shows the curves of the drying rate, the duration of which in the first and second periods is much longer for pasta subjected to hygrothermal treatment. Drying speed in the first period (N from) is higher for pasta that have undergone a 2-minute hygrothermal treatment and is 0.31% / min compared to 0.14% / min for products without treatment.

An increase in the duration of hygrothermal treatment from 2 to 5 minutes leads to an increase in the drying time by almost 2 times (see Fig. 1), which is explained by the deepening of the starch gelatinization zone, resulting in the formation of stronger moisture bonds with this component of the dough. The drying rate at a 2-minute hygrothermal treatment both in the first and in the second period is higher than at a 5-minute hygrothermal treatment (see Fig. 2). Comparison of the curves of drying and its speed during hygrothermal treatment in the range of 1-5 minutes shows that a 2-minute treatment is optimal in terms of the total duration of drying. By mathematical processing of experimental data carried out on a computer BESM-6, equations for the curves of drying pasta in 1 and in 2 periods and drying rates were obtained:

For the first period: (from W to W)

W = B - A; - A = N (1)

where W is the current humidity corresponding to the 1st drying period,%;

W is the first critical moisture content of pasta,%;

W - initial moisture content of pasta,%;

Drying duration in 1 period, min;

В, А - coefficients of the equation (В -%, А -% / min);

Drying speed,% / min;

Fig. 2 Curves of the drying rate of pasta:

1, 2 - with hygrothermal treatment for 2 and 5 minutes, respectively; 3 - without hygrothermal treatment.

For the second period: (from W to W, with W tending to W)

W = W + C exp (-m)

differentiating equation (2), we obtain the drying rate equation

M C exp (-m), (2)

where W is the second critical humidity,%;

W - equilibrium humidity,%;

W - current humidity corresponding to the 2nd drying period,%;

Duration of drying in the 2nd period, min;

C is the equation coefficient,%;

m - exponent degree, 1 / min;

Drying speed in the 2nd drying period,% / min.

Table 1 shows the numerical values ​​of the coefficients of equations (1) and (2) of the drying curves and the drying rate of pasta depending on the parameters of hygrothermal treatment and drying.

Table 1

Hygrothermal treatment parameters				Equation coefficients
				1 drying period		2 drying period

BIOCHEMICAL CHANGES OF STARCH AND PROTEIN OF PASTA PRODUCTS AND THEIR TECHNOLOGICAL CHARACTERISTICS DURING HEAT TREATMENT AND DRYING

Kinetics of the drying process of hygrothermally processed pasta... In industry, for drying tubular pasta, a "soft" three-stage pulsating mode is used, often changing the drying capacity of the air.

The use of preliminary hygrothermal treatment of raw products made it possible to apply more "stringent" modes with a constant drying capacity of air. As a result, cracking of products is excluded, both during drying and during long-term storage. This is also facilitated by the introduction into the drying process of the final technological operation - the stabilization of products, which in its physical and chemical essence is similar to the conditioning of products.

The mode of drying with heated air (without pre-treatment with steam) is characterized by the following parameters: air temperature (); relative humidity (); air speed ().

With the introduction of hygrothermal treatment, a fourth parameter appears - the duration of hygrothermal treatment (). These parameters affect not only the drying rate, but also the critical equilibrium moisture content of the material, as well as the properties and quality of the product. Therefore, it is necessary to find such a drying mode, which, with the minimum drying time and the least energy consumption, will ensure the high quality of the finished products.

The kinetics of the process of drying pasta, subjected to preliminary hygrothermal treatment, was studied in the range of parameters: relative air humidity from 50 to 80%; air temperature from 50 to 80 ° С; air speed from 0.5 to 2.0 m / s.

Studies have shown that the drying of hygrothermally processed pasta proceeds the more intensively, the lower the relative humidity and the higher the temperature and speed of the drying agent. However, the final judgment on the values ​​of the optimum humidity, temperature and speed of the drying agent is possible only taking into account the quality indicators of the finished products. The assessment of the quality of the products was carried out according to the following indicators: acidity, color of products, strength on the Stroganov device, culinary properties (the amount of dry substances passing into the cooking water; coefficient of increase in volume; increase in the mass of pasta during cooking; duration of cooking). Changes were investigated: attackability of starch by amylolytic enzymes and protein substances by proteolytic enzymes; and also the content of nitrogen in the cooking water and water-soluble nitrogen under the action of hygrothermal treatment.

Biochemical changes in starch and protein of pasta during hygrothermal treatment and drying. The structure of the starch is of great importance in determining the properties of the produced pasta. Commodity and culinary properties of products depend on it. One of the ways to find out the degree of starch change is to determine its attackability by amylases.

It is known that mechanical or thermal action on starch grains increases the rate of attack by their amylases. Starch subjected to processing (mechanical, heat, etc.) is saccharified by β-amylase rather than untreated starch. In this case, the attackability of starch increases most noticeably under the action of wheat β-amylase. Experiments were carried out to determine the attackability of starch by amylases under the action of hygrothermal treatment and under various drying parameters. The attackability of starch was determined by an increase in the content of reducing sugars formed under the action of an enzymatic extract of β-amylase (glycerol extract from wheat flour) in a dough at a temperature of 40 ° C for 1 hour; it was expressed in milligrams per 10 g of dry substance of the dough in terms of maltose. Changes in the biochemical characteristics of pasta during hygrothermal treatment and drying are given in Table 2.

From the data in Table 2, it can be seen that the attackability of starch by β-amylase in pasta without hygrothermal treatment was 100 mg per 10 g of dry matter of the dough in terms of maltose, and after processing the pasta with steam for 2 minutes it increased to 236.5 mg, i.e. .more than 2 times. Moreover, with an increase in the duration of hygrothermal treatment, the attackability of starch by β-amylase increased and with a 5-minute treatment was 253.5 mg. An increase in attackability is, therefore, associated with partial gelatinization of starch during heat treatment of products with steam, which is in good agreement with a slowdown in the drying rate with an increase in the duration of hygrothermal treatment. The parameters of the drying agent also influenced the attackability of starch amylase. With an increase in its temperature from 50 to 60 ° C, the attackability increased from 156 to 236.5 mg. A further increase in temperature led to inactivation of β-amylase, which caused a decrease in the attackability of starch. So, this indicator at a temperature of 70 and 80 ° C decreased, respectively, to 190.5 and 166 mg. At a relative humidity of 60%, the attack rate was 219 mg, and at 80% - 236.5 mg. Starch attack by β-amylase at air speed m / sec: 0.5 - 167; 1.0-236.5; 1.5 - 225; 2.0 - 204 mg.

The starch attack rate was found to be sensitive to changes in relative humidity and drying agent speed. At a constant air temperature of 60 ° C), an increase in its relative humidity and speed up to 1.0 and / sec, the attackability of starch increased, which was explained by the deepening of its gelatinization due to more intensive heating of the products.

Hygrothermal treatment of products causes denaturation of gluten proteins, which become less soluble and lose their catalytic activity. The attackability of protein substances by proteolytic enzymes was assessed by the accumulation of water-soluble nitrogen. From the results shown in table. 2, it can be seen that the attackability of protein substances of pasta without hygrothermal treatment was 39.0%, and with a 2-minute steam treatment - 30.35%. With an increase in the duration of hygrothermal treatment to 5 minutes, the attackability decreases to 27%. Thus, it has been established that as a result of hygrothermal treatment, thermal denaturation occurs, contributing to a decrease in the activity of protein substances. The drying process also causes significant protein denaturation even with a mild heat treatment. In this regard, it is of interest to trace how the activity of protein substances changes depending on the parameters of the drying regime. In terms of the attackability of protein substances, drying parameters can be recommended.

table 2

Duration of hygrothermal treatment	Drying agent parameters			Starch attack by wheat β-amylase, mg maltose per 10 g DM	Attackability of protein substances on the accumulation of water-soluble nitrogen,
	relative humidity	temperature	Speed

An increase in the air temperature in the drying chamber affects the attackability of protein substances in different ways. Thus, with an increase in temperature from 50 to 70 ° C, the attackability of protein substances increased from 29.6 to 31.6%, a further increase in temperature reduced the attackability to 25.6%. Changing the speed of the drying agent also affects the attackability of protein substances in different ways. At a speed of m / s: 0.5 - 26.96; 1.0-30.3; 1.5 - 34.05, and at 2.0 - 32.7%. Considering the influence of the parameters of the drying agent on the attackability of protein substances, we see that when drying hygrothermally treated tubular pasta, the optimal air temperature is 60-70 ° C, the air speed is 1.0-2.0 m / sec. At the same time, the changes in the protein-proteinase complex in pasta were checked using hygrothermal treatment. At the same time, the amount of total nitrogen in the cooking water and water-soluble nitrogen was determined. As a result of hygrothermal treatment, the amount of nitrogenous substances in the cooking water was reduced. Thus, with an increase in temperature from 50 to 70 ° C, the attackability of protein substances increased from 29.6 to 31.6%, a further increase in temperature reduced the attackability to 25.6%. Changing the speed of the drying agent also affects the attackability of protein substances in different ways. At a speed of m / s: 0.5 - 26.96; 1.0-30.3; 1.5 - 34.05, and at 2.0 - 32.7%. Considering the influence of the parameters of the drying agent on the attackability of protein substances, we see that when drying hygrothermally treated tubular pasta, the optimal air temperature is 60-70 ° C, the air speed is 1.0-2.0 m / sec. At the same time, the changes in the protein-proteinase complex in pasta were checked using hygrothermal treatment. At the same time, the amount of total nitrogen in the cooking water and water-soluble nitrogen was determined. As a result of hygrothermal treatment, the amount of nitrogenous substances in the cooking water was reduced.

Change those x nological characteristics of finished products. The drying process significantly affects the quality of the finished product, and the choice of the optimal parameters depends on the quality indicators of the finished product. The taste or defects of pasta are judged by their acidity, which, according to GOST, should not exceed 3-4 degrees. The color of the pasta should be yellowish, typical of flour made from durum wheat. A number of factors affect the color of the finished product; color of raw materials, conditions of the technological process, etc.

As studies have shown with the use of hygrothermal treatment, the color of the products changes dramatically, they acquire a pleasant amber-yellow color; at the same time, the surface of the pasta becomes glossy and their strength increases significantly. The strength of products (determined on the Stroganov device) without hygrothermal treatment at a "hard" drying mode is below the GOST value and is equal to 606 g. their properties during cooking are: the duration of cooking until cooked, an increase in the mass of cooked products, loss of dry matter in the cooking water, an increase in the volume of pasta during the cooking process. All these indicators were determined using standard methods. The amount of dry matter transferred into the cooking water using hygrothermal treatment decreased and amounted to 4.21% compared to 5.19% (without steam treatment), while the volume increase coefficient slightly increased from 3.28 to 3.32 times and was within the acceptable limit. The increase in the mass of pasta during cooking decreased in pasta produced using hygrothermal treatment (for 2 minutes), from 173 to 168%. The relative humidity of the air also affected the cooking performance. Thus, an increase in the relative humidity of the air from 50 to 80% contributed to a decrease in the amount of dry substances passing into the cooking water, a decrease in the coefficient of increase in volume (from 3.5 to 3.32 times) and an increase in the mass of pasta during cooking. The temperature and speed of the drying agent did not significantly affect the cooking performance.

We also note that the use of hygrothermal treatment helps to reduce the duration of cooking products to readiness from 20 to 10 minutes. The appearance of cracks in the products was fixed 3-4 hours after drying.

Considering the main technological indicators of pasta, it can be concluded that the use of hygrothermal treatment significantly increases the quality of the finished product. Conditioning of pasta. The use of "hard" drying modes will cause the risk of cracking on the surface and in the deep layers of the products, even if the structure of the macaroni tube is significantly hardened. The reasons for the formation of cracks lie in the unevenness of drying, shrinkage processes and the occurrence of shear stresses that exceed the maximum permissible values.

The stronger the structure, the less the likelihood of cracking, however, a full guarantee of cracking prevention is possible when switching to "soft" drying modes or using conditioning (stabilization) of products at the final stage of drying when they reach a humidity of 18%. The purpose of conditioning (stabilization) is to relieve stresses that have arisen during the drying process of pasta in a "hard" mode.

Conditioning was carried out as follows: pasta in the working chamber of the installation was treated with a steam-air mixture with the required parameters. In this case, the dried products were moistened to about 14%, and the outer layers reached a higher moisture content than the inner ones. As a result, the wet layers were stretched and the shear stresses were relieved. After conditioning, the products were kept in air. During stabilization, the products were cooled down to the room air temperature, and their humidity reached a standard value.

CHANGE IN THE STRUCTURAL AND MECHANICAL PROPERTIES OF PASTA PRODUCTS SUBJECT TO HYGROTHERMAL TREATMENT

After hygrothermal treatment, the products are hardened, though. But they remain quite flexible. Cracking and warping of pasta is due to the uneven distribution of moisture inside the material, as a result of which a volumetric stress state occurs. Normal tensile stresses and shear stresses may exceed the limit values ​​and cause structural failure.

It is of interest to find out the main rheological characteristics of pasta dough subjected to hygrothermal treatment at different humidity levels, since they determine the normal and shear stresses in the material,

NOT. Netushil conducted tensile tests on pasta dough. However, with the use of preliminary hygrothermal treatment, this method of determining rheological characteristics cannot be applied, because, starting with a moisture content of 34%, the products become sufficiently strong, and the used specimen clamps do not allow tensile tests: the pasta dough slips out of the clamp and breakage does not occur in the middle, as required by the technique, but near the clamped end of the sample. Compression tests were performed on the dried products. For the study, a sample of pasta was taken with dimensions (mm): length - 50, external and internal diameters, respectively, 7 and 4.5.

Changing the sample size slightly changes the test results, which is explained by the influence of the scale factor.

The main criteria for assessing structural and mechanical properties are strength and characteristic parameters of the relaxation process (elastic-kinetic and rheological). In the works of I.S. Melnikova and N.E. Netushil describes the influence of the moisture content of products on the change in the process of drying plastic-elastic deformations. However, there is no data on what adjustments to this relationship can be made by preliminary hygrothermal treatment of the drying object. To study this issue, MTIPP manufactured a special device for measuring the load at a constant strain rate on compression of a macaroni tube in the longitudinal direction.

The device (Fig. 3) consists of an electric motor, which, using a belt drive, drives the screw (the transmission system from the electric motor to the screw allows you to change the speed in a ratio of 1: 2: 4)

Rie.Z. Diagram of the device for studying the rheological characteristics of pasta during the drying process:

1 - electric motor; 2 - belt drive; 3 - screw; 4 - elastic element; 5 - oscilloscope; 6 - strain amplifier

The load applied to the pasta tube in the axial plane along the entire length of the generatrix of the perpendicular axis is transferred to an elastic element - a steel beam of rectangular cross-section, lying on two supports. Under the action of the load, not only the beam is deformed, but also the resistance strain gauges tilted onto it and assembled into a bridge circuit. From the measuring diagonal, the current through the amplifier is transmitted to the oscilloscope and recorded on the compression diagram of the macaroni tube. Plotting the load along the ordinate of this diagram, and the absolute compression of the tube along the abscissa, proportional to the loading time. The compression test was carried out at the following stages of the technological process: after pressing after hygrothermal treatment, at certain intervals during the entire drying process. The applied load varies from zero to the amount of compression or failure of the sample. Equilibrium is maintained between the applied load and the internal forces in the sample at each moment of time. The relationship between stress σ and strain ε of a pasta sample is plotted on an oscillogram.

According to the diagram of the change in σ = f (ε) at different values ​​of the moisture content of the dough, it is possible to trace the change in the main structural and mechanical indicators both in the process of hygrothermal treatment and in the process of drying.

Table 3 shows the results of the main structural and mechanical parameters of the macaroni tube. As can be seen from the data in the table. 3, preliminary hygrothermal treatment significantly changes the rheological parameters. So, - increases by an order of magnitude from 8 kPa to 23 kPa, the maximum compressive stress m ax, shear stress ks, the modulus of elastic deformations E (conditional) increases by 2 times, and the modulus of elastic-plastic deformations E decreases from 727 kPa to 5 77 kPa, which once again confirms the conclusions about the strengthening of the structure of products produced with the use of preliminary hygrothermal treatment.

Technology of bread, confectionery and pasta Table 3

The rheological characteristics undergo a significant change in the process of further drying, with two periods differing (1 period corresponds to a constant drying rate, 2 - to a decreasing rate). In the first period, all rheological characteristics remain unchanged, and at a moisture content of W = 33.2 close to the critical moisture value, the main structural and mechanical parameters begin to increase. With a moisture content of 33.2, the value of the modulus of elastoplastic deformations E begins to approach the value of the conditional modulus of elasticity E, while the attenuation of plastic deformation of the product mainly acquires elastic properties.

Figure . 4 shows the curves of changes in the maximum stress of the macaroni tube during the drying process. The curves have two characteristic sections. The inflection point lies on the border of the transition from the first to the second drying period, which at the same time corresponds to the transition from the plastic state of the substance to the elastic one. In the experiments, the initial moisture content and the maximum compressive stress of the products are the same W = 45% , m ax = 105 kPa. As a result of hygrothermal treatment, the products are moistened to W = 54.6%, and the maximum compressive stress increases to m ax = 200 kPa. From this moment, the difference between the values ​​of the maximum compressive stress of products subjected to hygrothermal treatment and without it is equal to 100 kPa, and by the end of drying at W = 16% this difference increases to 750 kPa,

The points of transition from a straight section to a curvilinear one do not coincide either in the value of humidity or in the magnitude of the maximum compressive stress. The transition to an elastic state in pasta subjected to hygrothermal treatment occurs with an advance (by 4 - 5%) in comparison with products without treatment. From the given graphs it follows that the hygrothermal treatment of products leads to their significant strengthening. During the drying process, many materials, including pasta, reduce their size, i.e. shrinkage occurs. If the drying process is not carried out correctly, the pasta will crack. The reason for the latter is the uneven shrinkage of the layers of the material to be dried. Intensive modes of drying pasta are limited by their shrinkage.

Hygrothermal treatment leads to hardening of the pasta structure caused by protein denaturation. In turn, denaturation of proteins helps to reduce the size of the material. But hygrothermal treatment increases the mass of the substance by moisturizing the products. This explains the unchanged dimensions of the steamed pasta.

Fig. 4. Curves of changes in the maximum compressive stress of the macaroni tube during the drying process:

1 - without hygrothermal treatment; 2 - with a two-minute hygrothermal treatment

However, in the process of drying, the shrinkage pattern of the macaroni tube of hygrothermally treated pasta differs from that of conventionally prepared pasta. According to the experimental data, the coefficients of linear shrinkage for two periods of drying and, the relative shrinkage δ, the coefficients of volumetric shrinkage β and volumetric shrinkage δ are established. Comparing the values ​​of the coefficients of linear and volumetric shrinkage of pasta without and with hygrothermal treatment, it can be seen that steam treatment helps to reduce the coefficient of linear shrinkage. The volumetric shrinkage ratio is also reduced with the use of hygrothermal treatment. Such a change in the linear and volumetric shrinkage in connection with the use of hygrothermal treatment makes it possible to dry pasta in a "hard" mode, since the possibility of cracking is reduced.

But the risk of cracking still remains, and especially in the second stage of drying. Kirpichev's criterion can be taken as a criterion for assessing the risk of cracking:

K (3)

where is the mass flow;

Determining size;

Average moisture content corresponding to the Fourier criterion

It is important to note that with the usual drying method, the maximum allowable value of Kirpichev's mass transfer criterion for pasta is about 0.6 . The use of preliminary hygrothermal treatment contributes to an increase in strength and leads to the fact that products are able to withstand higher shear stresses. Therefore, the maximum allowable value of Kirpichev's mass transfer criterion for pasta that has undergone preliminary hygrothermal treatment increases to 1.3 , which indicates a decrease in the possibility of cracking.

As can be seen from the data obtained, hygrothermal treatment has a significant effect on the structural and mechanical characteristics of pasta.

Changes in structural and mechanical indicators in strengthening the structure of products are one of the main factors in the intensification of drying of products subjected to preliminary hygrothermal treatment, products become "susceptible" to maintaining a "hard" drying regime.

MASS EXCHANGE CHARACTERISTICS AND EQUILIBRIUM AND CRITICAL HUMIDITY OF PASTA PRODUCTS

The kinetics of mass transfer of matter in wet materials is determined by the difference in mass transfer potentials. The molecular-kinetic theory of heat and mass transfer phenomena assumes that, under isothermal conditions, the moisture flux density is directly proportional to the gradient of the mass transfer potential:

q kg / mh, (4)

where is the gradient of the mass transfer potential,;

The coefficient of mass conductivity, which determines the ability of a wet material to transfer moisture at the magnitude of the potential gradient, kg / m.h .;

Mass transfer degree.

Since the thermodynamic potential of mass transfer under isothermal conditions is an unambiguous function of moisture content, the gradient of the mass transfer potential can be expressed through the gradient of moisture content:

where is the gradient of moisture content kg · moisture / kg · DM · m;

Specific moisture content of a wet body, kg · moisture / kg · CB ·;

Taking into account formula (5), the basic law of isothermal mass conductivity can be represented as follows:

q (6)

de is the density of an absolutely dry body, kg · DM / m;

The coefficient of internal mass transfer (depends on temperature and moisture content), characterizing the properties of the body in relation to the intensity of the development of fields of the potential of mass transfer or the inertial ability of the body to external water disturbances.

Consequently, the rate of drying mainly depends on the coefficient of internal diffusion of moisture. An analytical determination of the coefficient of internal mass transfer was carried out from the drying curves and the drying rate according to the following formula:

(7)

where R is the characteristic size of the body, m;

Drying rate,% / m;

External mass transfer coefficient, m / h.

Equilibrium moisture, kg / kg.

(For a pasta tube, if R = 3.5mm, = 2.25mm, ratio = 0.625mm)

The nature of the change in the coefficient of internal diffusion of moisture during drying with hygrothermal treatment and without it is similar. In the first period of drying, it remains constant, and during the period of a falling drying rate, it changes slightly, but decreases 2 times in absolute value,

During a period of constant speed, moisture will move in the form of a liquid (selective diffusion of osmotically retained moisture), the temperature of the material will be constant and equal to the temperature of the wet bulb.

Upon reaching the first critical point on the surface of the material, corresponding to hygroscopic humidity, the drying rate will begin to decrease, and the movement of adsorbed moisture inside the material will mainly occur in the form of steam. It should be noted that in the second period the rate decreases linearly, this regularity is in accordance with the change in the internal diffusion coefficient during this drying period. The external moisture exchange coefficient changes in the same way. Figure 5 shows a diagram of changes in the coefficients of external moisture exchange and internal mass transfer for pasta subjected to preliminary hydrothermal treatment and dried according to the generally accepted technology. These coefficients, both in the first and in the second periods, are higher for products that have undergone preliminary hygro-heat treatment, which once again testifies to the intensification of the drying process.

Fig. 5. Diagram of changes in the coefficients of external moisture exchange and internal mass transfer a m of pasta with the introduction of hygrothermal treatment:

1,2 - drying pasta, respectively, without heat treatment and with heat treatment

Table 4 shows the values ​​of the coefficients of external moisture exchange and internal mass transfer for various regime parameters of hygrothermal treatment and drying. The coefficients of internal diffusion and external moisture exchange depend on the duration of the hygrothermal treatment and on the parameters of the drying mode.

Table 4

Hygrothermal treatment parameters				Moisture coefficients of pasta

From the data in Table 4 it can be seen that the largest values ​​of these coefficients are observed with a 2-minute hygrothermal treatment. The coefficients of external moisture exchange of internal diffusion decrease with an increase in the relative humidity of the air, a decrease in the temperature and speed of the drying agent.

Equilibrium and critical moisture content of pasta. By the method of analytical processing of the drying curves and the drying rate, the values ​​of the equilibrium and critical moisture content of pasta were obtained (Fig. 6).

It should be emphasized that heat treatment leads to some decrease in the equilibrium moisture content of the finished product. This factor is of practical importance, indicating an increase in the stability of pasta during storage.

Fig. 6. Graph of the effect of heat treatment on the first critical point W

and equilibrium moisture W

In addition to the results obtained, the effect of heat treatment on the first critical moisture content of pasta was investigated (see Fig. 6). It can be seen from the graph that the first critical moisture content of products subjected to preliminary hygrothermal treatment increases (especially after a 2-minute treatment). This is important for practical technology, since this point is associated with the transition from the plastic state of the substance to the elastic one. The first critical point shifts towards an increase in products prepared using the new technology.

INSTALLATION FOR DRYING PASTA PRODUCTS ACCORDING TO NEW TECHNOLOGY AND JUSTIFICATION OF THE PERFORMANCE OF IMPLEMENTATION OF A NEW DRYING METHOD

Hanging dryers for drying long pasta are currently known. These include dryers in the LMB line and foreign ones - Braibanti (Italy) and Buhler (Switzerland). These dryers of continuous action are equipped with drying chambers for preliminary, final, stabilization. Drying of long tubular products in these installations is carried out in "soft", three-stage pulsating modes, with a long time (18-24 hours) for drying. In addition, the listed dryers are bulky, their length reaches 30-45 m.

In connection with the use of preliminary hygrothermal circulation before drying and conditioning at the end of it, it became necessary to create a design for the dryer, which included new technological operations.

Figure 7 shows a diagram of the installation for drying long-tube pasta in a suspended state. The installation consists of chambers: preliminary hygrothermal treatment, curing, drying, conditioning, transitional vona and a chamber for stabilizing dried products. The drying unit is equipped with an air supply chamber and steam supply devices. After the press, bastuns with a semi-finished product are fed into a preliminary hygrothermal treatment chamber, where they are exposed to a mixture of air and steam for 2 minutes. Then the products enter the storage chamber, after which they are sent to the drying chamber, where they move along the tiers from bottom to top. When the products reach the upper tier, their moisture content reaches 13%. To relieve internal stresses, the dried products are sent to the conditioning chamber where they are moistened to a moisture content of 16% in an air-vapor environment within 1-2 minutes. After the conditioning stage, the products are fed into a stabilization chamber, in which they cool and dry to a standard moisture content of 13%.

The duration of the process of hygrothermal processing and drying of pasta for various types of flour in the proposed drying unit reaches 8 - 10 hours. Thus, the use of a new technology for the preparation of long-tube pasta can reduce the duration of the drying process by 3 times; apply "hard", constant parameters of the drying agent; reduce overall installations; improve product quality.

Fig. 7. Drying plant diagram

1, 2, 3, 4, 5, 6 - hygrothermal treatment chamber, respectively; maturing, drying, transition zone, conditioning, stabilization of dried products; 7 - hole for unloading finished products; 8 - chamber for air supply; 9 - device for supplying steam; 10 - hole for loading products

Justification of the feasibility of introducing a new method of drying. Table 5 shows a comparison of the technical characteristics of the existing LMB line and the one reconstructed using a new method.

From the data table. 5 it follows that the introduction of a new drying method can significantly reduce the drying time and reduce the dimensions of the drying unit (in length) by 2 times.

Table 5

The developed drying unit allows placing a modern automatic line for the production of pasta in existing pasta factories during their reconstruction.

Other advantages of introducing a new drying method are as follows:

Breakages in the initial stage of drying are eliminated due to significant strengthening of the structure of raw workpieces (blockages of drying installations by breaks of strands are practically excluded during suspended drying of products made of weak flour);

The taste of the products improves (obviously, as a result of a severe drying regime, the reaction of melanoidin formation occurs); the culinary properties increase in comparison with ordinary pasta: they boil down faster, with a prolonged stay in boiling water, the products retain their individuality; the amount of all extractives passing into the cooking water is reduced.

By reducing the duration of the technological process (3 times), it is possible to increase the volume of products per unit of drying area per day also 3 times. Since the occupied area for the new line will be 2 times less than the area required to install the LMB line, it seems possible to place 2 new lines that implement the drying process according to the proposed method. In this regard, the production output increases 6 times. However, the use of a new drying method based on hydrothermal treatment leads to a slight increase in steam consumption per hour, but in general this economic indicator in terms of the total drying time will decrease from 5750 to 2790 kg. Air consumption for the entire drying period will also be reduced by 52,000 m³.

Thus, the prime cost of pasta will decrease due to a decrease in depreciation deductions for the consumption of air, electricity and steam.

Analysis of literary sources shows that currently there are two directions in the intensification of the process of sushi pasta:

Preliminary hydrothermal treatment of the semi-finished product before drying;

Adding surfactants to the pasta dough.

It should be noted that the most widespread was the first method of intensifying the drying process.

MTIPP has developed a technology for a continuous drying process under the "hard" mode of long-tube pasta, which is characterized by the use of preliminary hygrothermal treatment and conditioning of the products.

It has been established that hygrothermal treatment of raw products in combination with other technological factors of drying significantly improves the set of quality indicators of finished pasta, strength and fracture structure, appearance and their culinary properties.

On the basis of the developed technological modes of hygrothermal treatment, drying and conditioning of pasta, a diagram of a new drying unit is proposed in which the drying process is reduced to 8-9 hours while improving the technological and structural-mechanical properties of finished products.

By reducing the duration of the technological process by 3 times, it is possible to increase the volume of output per unit of drying area per day also by 3 times, and reduce the cost of pasta by reducing depreciation charges: air, steam and electricity consumption.

LITERATURE

1. Taranov I.T. Convective multistage modes for drying pasta in flat cassettes. "Kharchova Promislovist". K., 1973.2, p. 42-46.

2. Chernov M.E., Polyakov E.S., Burov L.A., Savina I.M. Drying of pasta in rocking, rotating, cylindrical cassettes. (Information). TSINTIPishcheizdat, M., 1971.

3. Kaloshina E.N., Demchenkova E.A., Divtsivadze G.V. Influence of various methods of heat treatment on the quality of pasta. Sat. scientific works ZIST department. "Commodity Science of Food Products". M., 1973.

4. Ginzburg A.S., Kaloshina E.N. Study of the kinetics of drying long tubular pasta. "Bakery and confectionery industry". "Food industry" 1, 24-25, M., 1973.

5. Ginzburg A.S. Fundamentals of the theory and technology of drying food. Publishing house "Food Industry", M., 1973 .

6. Kaloshina E.N. Investigation of the drying process of long tubular pasta. Diss. to apply for an account. degree Ph.D., M., 1973.

Drying of formed cut pasta is the final stage of pasta production, on which the quality of the product depends. It is carried out in special dryers, in which the convective method of heat supply is used.

Drying plant for pasta consists of a chamber where the product is dehydrated; air heater, where the drying air is heated; supply and exhaust system for heated supply and exhaust air removal.

The heater can be located both inside the drying chamber and outside it. Depending on the method of heating the coolant, heaters with water or steam heating are used.

Depending on the design, drying plants are divided into drum, conveyor and cabinet, and according to the principle of operation - into continuous, cyclic and periodic.

Pasta drying plants differ in the ways of placing the material to be dried inside the chamber (frames, cassettes, bastuns, cells) or devices for moving it.

The classification of pasta dryers is shown in Fig. 22.

Fig. 22. Classification of dryers for pasta

Equipment for drying short pasta

Pre-dryer installation

The installation is designed for the primary drying of pasta, carried out in order to prevent sticking during further drying. Such installations are completed with automated lines for the production of short pasta.

The Braibanti pre-drying plant consists of two identical sections (left and right), operating simultaneously and independently of one another. The sections are rigidly connected with ties and have a common lining, which gives the installation the appearance of a single finished structure. The installation is located under the press platform, between its supports.

The main units of the installation (Fig. 23) are a sieve block with a drive mechanism and a heating and ventilation system. Each section has a welded frame 1 made of steel angle bars. Inside each section, five vibrating metal sieves are arranged one above the other 8. Each sieve is a stainless steel mesh stretched over a rectangular wooden frame and fixed in a metal frame. At the ends of each of the four top sieves (along the product path) there are rectangular windows through which the raw products are poured from top to bottom from the sieve to the sieve. The lower sieve is connected to a tray 6, which protrudes beyond the chamber from the side opposite to the loading.

On the wall of the frame from the unloading side of the products, a sieve drive is fixed, consisting of an electric motor, a V-belt transmission with two-stage pulleys, an eccentric shaft and two pairs of connecting rods.

The first pair of connecting rods is connected to a set of the first, third and fifth sieves, the second to a set of the second and fourth sieves. During the operation of the installation, the sets of sieves reciprocate in opposite directions relative to each other, which ensures the movement of raw products along the first, third and fifth sieves forward, along the second and fourth - in the opposite direction.

Thus, moving along the sieves from top to bottom, the raw product successively passes about 10 m, during which time up to 2% of moisture is removed from the products.

Fig. 23. Installation "Braibanti" for preliminary drying

On the end sides of the frame of the chamber of each section under the sieves, there are two heaters 3 and two axial eight-blade fans 4. Hot water (90 ° C) is supplied to the heaters in an amount of 2.5 m 3 / h. Fans continuously blow hot air through the sieve stack. Air is taken from the shop floor through control gates 2 and 5 in the casing of the chamber. The centrifugal fan 7 installed on the end wall of the chamber section is designed to remove excess moist exhaust air from the section.

The casing of the chamber consists of a wooden frame, lined on the inside with wood-fiber boards 3 mm thick, on the other side - with paper-laminated plastic. Thermal insulating material - polystyrene - is laid between them. To facilitate access to fans, electric drives and air heaters, the chamber walls are removable.

Conveyor dryers

Dryer SPK-4G-45(fig. 24). It consists of the following main parts: five belt conveyors 4, two drive columns 12, steam heaters 2, a ventilation system 9 and a dryer control panel.

The frame 1 of the dryer is prefabricated metal, lined with metal shields on the outside, and has doors. To monitor the process of drying the product, taking samples, cleaning the nets and repairing, removable shields with windows 7 are installed on the sides of the dryer, and doors are installed on the front sides.

Fig. 24. Dryer SPK-4G-45:

1 -frame; 2 - air heater; 3 - mesh belt, 4 - belt conveyor, 5 - sliders;

6, 11-collector; 7 - window; 8-angle thermometer; 9 - ventilation system; 10 -boobers;

12-drive column

Inside the dryer, one under the other, there are five pairs of drums, each with a diameter of 340 mm, on which a metal mesh belt 3 2000 mm wide made of stainless steel is stretched, while the total drying surface of the belts is 45 m 2. Each pair of drums is offset in length relative to the other, which allows the product to be poured from belt to belt.

To clean the surface of the drums from the sticking product, scrapers are installed on all five tension drums. In places where the product is poured from the upper belt to the lower belt, rotary guides of gate 5 are installed.

The dryer is heated by steam finned heaters located between the leading and driven branches of the mesh belts of all five conveyors. The heater 2 of each conveyor consists of two batteries connected in series. Each battery consists of two longitudinal pipes with a diameter of 44.5 / 39.5 mm with holes into which 16 transverse pipes with a diameter of 38/33 mm are inserted.

On the transverse pipes, metal strips 30 mm wide and 1 mm thick are wound so that ribs are formed in the amount of 100 per 1 m of the pipe length. The heating surface of each air heater is 140 m 2, the total surface of the air heaters of the dryer is 700 m 2. The heat source for the heaters is steam, which is supplied from a steam power plant under a pressure of 0.3-0.8 MPa through a pipeline through a control valve, an inlet manifold 6, and from it through inlet valves to each tier of heaters.

Control over the pressure of steam entering the dryer is carried out by OBM-160 manometers installed on the inlet and outlet 11 manifolds.

The dryer is equipped with a ventilation system, which consists of two exhaust chambers made of 1.5 mm sheet steel and installed above the upper belt of the dryer.

Each chamber contains one axial fan. Inside the exhaust chambers, in front of the axial fans, rotary dampers 10 are installed, with which you can change the amount of exhaust air passing through.

The movement of the belt conveyors of the dryer is carried out from two drive columns 12. From the first, the first, third and fifth belt conveyors are driven. The rotation of the drive drums is carried out from an electric motor through a V-belt transmission, a chain variator, a chain transmission, a worm gear and a chain transmission system. From the electric motor of the first column through a V-belt drive, a worm gear and a chain drive, one shaft rotates with brushes installed at the end of the second belt conveyor.

The second drive column has a similar design, it drives the second and fourth driving drums of the conveyor belts, as well as the rotation of two shafts with brushes installed at the end of the first and third belts.

Above the three upper belts, there are turners, which are a shaft with rods fixed to it. It is located across the belt, and as the rods rotate, the dried products are mixed, preventing the formation of ingots.

With the help of a spreader, raw products are transferred to the upper belt of the dryer, where they rather quickly move over the heaters of the upper tier. This evaporates more than a third of the moisture to be removed.

Further, the product enters the second belt, which moves somewhat more slowly over the heaters of the second tier. Drying also continues quite intensively here, approximately one third of the moisture is removed.

Then the products go to the third belt, which moves even more slowly over the heaters of the third tier, about 4% of moisture is removed on this belt.

The fourth and fifth belts have even lower speeds, and during the time spent on them, the product finally dries up to standard moisture.

In the process of pouring products on the belts, fine flour crumbs are formed, which pass through the cells of the belts and are collected in the lower part of the dryer on pallets. Drying air passes through the dryer from bottom to top, is heated in heaters and cooled, passing through conveyor belts with the product. The moisture removed from the products is discharged into the atmosphere by means of exhaust fans.

Dryer SPK-4G-90. The dryer of this brand differs from SPK-4G-45 in that it has large working areas of conveyor belts and productivity. Dryer SPK-4G-90 with the same belt width (2000 mm), but due to its greater length, has a total working surface of 90 m 2.

The main disadvantage of steam conveyor dryers is that they use a mode with an increasing drying ability of air. Since the product flow and the drying air flow are directed towards each other, the drier products on the lower conveyor belts are dried with drier air than the raw products on the upper conveyor belts, and the effect of sagging of the conveyor belts is also observed.

Drum dryers

Drum dryer "Romet" installed in the automated line of the Italian company "Braibanti". Drum dryer "Romet" (Fig. 25) consists of two mesh cylinders with a diameter of 1600 and 2400 mm, inserted into one another.

Fig. 25. Drum dryer "Romet":

a - scheme; b - cells; one - partition; 2 - profile; 3 - window

The cylinders are fastened to each other by means of rims and 24 transverse ties. To give the structure the required rigidity, six hoops with special clamping devices are installed along the outer perimeter of the drum.

The inner space between the cylinders is divided by metal partitions (Fig. 25, b) 1, and each section along the entire length is divided by special curved profiles 2 into separate cells with windows 3 (50 cells). This design ensures, when the drum rotates, the product is poured into the cells and its gradual movement along the section. For one revolution of the drum, the products are poured from one cell to another, for 50 revolutions of the drum, the products pass through all the cells of one section in succession.

To ensure the necessary technological modes of the drying process, all four drums installed in series are covered with heat-insulating panels. Axial fans and heater banks are located between the top floor and the drying drums. Each dryer has six 1.1 kW axial fans and one centrifugal suction fan. Hot water is supplied to the entire line system with a 1.1 kW pump.

The regulation of the amount of fresh air taken into the dryer and the discharge of the spent air are carried out automatically in predetermined ratios. For this purpose, in the upper ceiling above each dryer there are three openings for fresh air intake, each of which is closed by dampers using a system of rods and a gearbox. A damper is also installed on the suction pipe of the centrifugal fan.

The product enters the first drying drum from the vibrating dryer through two vibrating trays. For this, two loading windows measuring 300x400 are provided in the lining of the end part of the drying tunnel. The ends of the vibrating trays are mounted on flexible vertical supports on the floor of the room. The transfer of the product from one dryer to another is carried out using a transfer device, which has collecting vertical and inclined chutes.

Long pasta drying equipment

Depending on the method of placing products inside the dryer, equipment for drying long pasta can be divided into three main groups:

The first one unites a group of dryers, where the method of drying pasta in tray cassettes is used. These are cabinet-type batch dryers VVP, 2TSAGI-700 and "diffuser". This group includes mechanized tunnel dryers of the Ufa and Volgograd macaroni factories and LS-2A designed by Rospishchepromavtomatika;

The second group of conveyor dryers of cyclic action is presented in the automated lines B6-LMG, B6-LMV of the Rostov-on-Don machine-building plant and the lines of the Italian company Braibanti. These dryers use a hanging method of drying pasta on metal bastuns;

The third group of continuous conveyor dryers is represented in the automated lines of the French company "Bassano". Here, a combined method of drying pasta is used in a preliminary dryer - on frames, in the final - in cylindrical cassettes.

Cabinet dryers

Cabinet dryers represent a cabinet closed on three sides with a channel for air passage and a slot for installing drying cassettes with products. The open part of the cabinet is used for loading and unloading products, as well as for the intake and discharge of air.

Dryer VVP(fig. 26). It is a drying chamber 1, open on one side for loading cassettes 2. In its upper part there is a casing in which a reversible fan 4 with an electric motor 3 and a collector 5 for directing air into a vertical channel 6 are installed. Inside the casing there is an axial reversible TsAGI fan No. 7.

The frame of the drying chamber is made of wooden blocks, sheathed with plywood and bolted for strength. The camera accommodates 156 double or 312 single cassettes. The camera accommodates three rows of cassettes in width, 26 in height; the length of double cassettes accommodates two rows, single ones - four rows. The working volume of the drying chamber is 2 m 3. The fan impeller is installed in a streamlined manifold that directs the air flow into the vertical channel. The use of a collector provides better conditions for the fan operation and contributes to an increase in its efficiency.

Fig. 26 Dryer VVP:

1- drying chamber; 2 - cassette; 3 - electric motor; 4 - fan; 5 - collector, 6 - channel

Drying of pasta is carried out at a temperature of 30-35 ° C and a relative humidity of 60-70%. Cassettes with pasta are fed from the machine for cutting and arranging pasta or from the cutting table on a conveyor or in trolleys to the drying room and stacked in the drying chamber. The reversible fan rotates in one direction, takes air from the workshop, directing it through the layer of products. This is followed by a short stop of the fan and its re-inclusion with rotation in the opposite direction, while the direction of the air flow is opposite to the initial one. Then the cycle is repeated.

The organization of the process of reversing the air flow in the drying chamber allows the product to be dried more evenly along the depth and cross-section of the cabinet. The total duration of the drying process is 14-16 hours. Cassettes with dried pasta are removed and transported to the filling department, and the cabinets are again filled with raw products.

Dryer 2TSAGI - 700(fig. 27). It is a drying chamber 3, open from two opposite sides, divided in height into two sections by a shelf 1, in which one axial reversible TsAGI fan No. 7 5 with an electric motor is installed each.

Fig. 27 Dryer 2- TsAGI-700:

1- shelf; 2- socket; 3 - drying chamber; 4 - grid; 5- fan; 6- trolley with products

On each open side of the cabinet there are 2 slots for loading cassettes.

Electric motors and fans on both sides are fenced with metal nets 4, which serve as restraints for cassettes when they are installed in the slots of the dryers.

The frame of the dryer is made of wooden blocks and sheathed with plywood. The stands for the installation of electric motors are welded from metal corners.

Dryers can be used as non-stationary ones; in this case, 1-2 trolleys 6 with products are placed to the fan head on each side. Each trolley holds 156 single or 78 double cassettes.

The 2TSAGI-700 dryer differs from the GDP in the increased air speed at the entrance to the products (4-5 m / s) and 1.5-1.8 m / s at the exit from them, due to the presence of two fans with almost the same cross-section of the nest. Increased air speed and a smaller area of ​​blowing of products by each fan provide more uniform drying of products in the layer, reduce the drying time and, accordingly, increase the removal of products from 1m 2 of the area occupied by the dryer.

Dryer capacity 1.0-1.2 t / day. with a process duration of 12-14 hours.

When operating the dryer, make sure that both fans rotate simultaneously in the same direction.

To evenly dry the product on both sides of the cabinet, these dryers also use a fan reversal.

Dryer "double-sided diffuser"(Fig. 28) consists of a ventilation chamber 2 with a one-sided or two-sided (as shown in the figure) "diffuser" and, accordingly, one or two drying chambers. Instead of cabinets, one or two trolleys can be rolled up to the ventilation unit and fastened with ties 5.

Each trolley holds 156 single or 78 double cassettes.

Reversible fan 4 is installed in the manifold 3. The fan motor is mounted on a metal welded support 1.

Fig. 28 Dryer "double-sided diffuser":

1 - support; 2 - ventilation chamber: 3 - collector; 4 - fan;

5- trolley with products; 6 - grid

From the ends, the collector is closed with protective metal grids 6.

In a "double-sided diffuser" drying air is drawn from the room on one or the other side of the dryer and passes through the pasta tubes located in the cassettes. As in the previous dryers, the rotation of the fans is periodically reversed.

The design of the relatively elongated diffuser contributes to the equalization of the air flow rate, which has a positive effect on the uniformity of drying over the section of the cabinet.

The operating mode of the dryer is similar to the previous ones.

Fig. 29. Tray drying cassettes:

but- wooden double, b- metal single

Dryers use tray wooden or metal cassettes (Fig. 29). Dimensions of wooden cassettes (in mm): single - 225x365x70, double - 454x365x70; capacity for dry products, depending on the assortment, respectively 2-2.5 and 4-5 kg. Metal cassettes are made of aluminum sheets with a size of 225x364x68 mm, the capacity of the cassette for dry products is 2-2.5 kg.

The disadvantage of cabinet dryers is that, for purely technical reasons, it is impossible to adjust the parameters of the drying air in the dryers themselves. Therefore, drying in them is carried out according to the mode of the shop without taking into account changes in the structural and mechanical properties of pasta during the drying process. The operation of such dryers requires significant manual labor. Many operations - transporting cassettes with products in the drying room and back, loading and unloading drying cabinets - are performed manually.

Therefore, in pasta enterprises, where there is an opportunity, cabinet dryers are replaced with other, more modern equipment.

Conveyor dryers

The peculiarity of such dryers is that cassettes with semi-finished products are stacked on chain conveyors, which, when moving, pass along the ventilation units. To ensure the required temperature conditions, the conveyors with the product and ventilation units are isolated from the drying room using a prefabricated metal frame lined with thermal insulation plates. Loading of cassettes with a semi-finished product is carried out from one side of the tunnel, unloading from the opposite.

Dryer LS2-A(fig. 30). It consists of the following main parts: a drying tunnel 7 with a set of axial fans 5, two chain conveyors 18 for moving the product, a conveyor 6 for returning empty cassettes, a ventilation system for supplying air to the drying tunnel and discharging exhaust air from it.

Inside the tunnel, along its entire length, twelve cabinets are installed close to each other, each of which contains two axial fans of TsAGI # 7 type. Axial fans in the cabinets are installed so that the direction of air movement of adjacent cabinets is opposite. This achieves a change in the direction of the air blowing on the pasta as it moves. On both sides of the cabinets, through the entire tunnel, there are two chain conveyors to move the product. From the loading side of the dryer, the conveyors leave it by 1300 mm, from the unloading side, roller conveyors 9 with a length of 7000 mm are installed to the chain conveyors. Roller conveyors serve as accumulators of finished products.

The chain conveyor is driven by an electric motor 13 through a V-belt speed variator 12 and three gearboxes 11 installed in series. Warm air is supplied to the drying chamber through the air duct 17 by a centrifugal fan 16 through a heater 15. The exhaust air is sucked from the upper zone of the dryer at the end of the tunnel by a centrifugal fan 14. A prerequisite for the operation of the dryer is some excess air pressure inside the drying tunnel, while the flow of air into the dryer through the door leaves and other gaps is not allowed.

The drying tunnel is divided into two drying zones: the first from the side of the entrance to the tunnel - the zone for preliminary drying of products, there are two cabinets in it; the second is the final drying zone, which includes ten cabinets. The drying zones are separated from each other by a partition, and there are doors for the cassettes to pass through them. In both zones of the drying tunnel, the required temperature (35-41 ° C) and relative humidity of the drying air (55-75%) are automatically maintained by adjusting the operation of the heater and electromagnetic valve.

The dryer operates in the following order. On two conveyors stacked close to each other stacks of cassettes 2 with raw pasta, 22 cassettes in height and two in width for each conveyor. A total of 2816 product cassettes are installed in the dryer. As the conveyor moves, the cassettes, with their mass, open the doors of the drying tunnel and are blown by the air flow from the axial fans. After drying, cassettes 10 with dried pasta are transferred from chain conveyors to roller ones, from which the products are sent to packaging. The return of empty cassettes is carried out by a belt conveyor, which has a direction opposite to the chain conveyors.

Cassettes 8 are placed one by one on the horizontal part of the belt conveyor located between the roller conveyors. The cassettes are transported over the drying tunnel to tray 1 for lowering them to the loading point. Rolling down the tray, cassettes can accumulate on its horizontal part, therefore, when the tray is filled with cassettes, under the action of their mass, the movable part of the horizontal guide of the tray is lowered and the limit switch is triggered, which stops the cassette return conveyor.

Fig. 30. Dryer scheme LS2-A:

1-tray; 2,8,10 cassettes; 3.11 gearboxes; 4.13-electric motor; 5- fan; 6-belt conveyor;

7-drying tunnel; 9-roller conveyor; 12-speed variator; 14.16-fans; 15-heater; 17-duct; 18-chain conveyor

Automated conveyor dryers

Long pasta is dried overhead using low-temperature drying modes, mainly in dryers of automated production lines B6-LMV and B6-LMG and other foreign firms (Braibanti, Pavan, etc.).

Removing moisture from raw products hung on bastuns is carried out in two stages: in the preliminary and final dryers. Pre-drying takes place under relatively severe conditions in the first drying chamber and final drying in intermittent mode (alternating drying and tempering) in the second drying chamber.

Pre-dryer B6-LMV(fig. 31). Designed for preliminary drying of long products on the lines B6-LMV and B6-LMG. The same dryer is installed on the Braibanti line with a capacity of 24 tons / day. The preliminary dryer B6-LMV is a heat-insulated and pressurized tunnel 5, which houses three comb conveyors 7.

The tunnel is divided by a ceiling into two floors, which form two drying zones. In the first (lower) zone there is one comb conveyor, in the second (upper) - two. At the bottom of the dryer there is a conveyor 7 for returning empty bastuns.

The dryer frame is assembled from separate welded sections that are bolted together. Dryer assembly elements are installed inside and outside the frame.

The dryer drive transmits the movement to the mechanism for moving the bastuns 9 in the horizontal direction to the chain conveyor 6, which transfers the bastuns from tier to tier (from one comb conveyor to another) or from the preliminary dryer to the final one.

Fig. 31. Pre-dryer B6-LMV

The dryer drive transmits movement to the mechanism for moving the bastuns 9 in the horizontal direction and to the chain conveyor 6, which transfers the bastuns from tier to tier (from one comb conveyor to another) or from the preliminary dryer to the final one.

The bastuns are moved horizontally using comb conveyors. Each conveyor consists of a pair of parallel guides and combs.

The guides are attached to the inner surfaces of the walls of the dryer, on which the trunnions of the bastuns with the products lie. The combs move along a closed quadrangle:

Rise - the pins of the bastuns lie in the depressions of the combs and rise above the guides;

Forward movement - bastuns with products move along the drying tunnel by one step equal to 31 mm;

Descent - the pins of the bastuns lie on the guides, and the combs go down; - backward movement - the bastuns remain in place, and the combs do idle in the opposite direction.

Thus, the bastuns with products gradually move along the tunnel of the dryer, and on the first and third conveyors - in one direction, and on the second - in the opposite direction.

The drying air is heated by means of 3 ribbed tube heaters. Each drying zone has its own air heating system.

The heating system of the first zone is supplied with water with a temperature of 80 ... 90 ° C directly from the central heating system of the factory. To enable condensation of water vapor in the lower zone of the bear, pipes are laid in the floor through which hot water circulates.

The ventilation system of the first and second drying zones works with partial recirculation of the drying air: humid air from both drying zones is partially discharged into the room, and partly mixed with the drier air entering the dryer from the room.

The ventilation of the first zone is carried out by axial fans 4, arranged in pairs: two fans near the entrance of the products into the dryer suck in air and rooms, blow it through the heater, create an air curtain and supply heated air to the lower zone; four pairs of fans provide recirculation of drying air by blowing it through the air heaters. Part of the moist air is discharged into the room.

Ventilation of the second zone is provided by eight centrifugal fans 8, located in pairs on the sides of the dryer. Three pairs of fans recirculate the drying air by partial suction of air from the room, and one pair sucks humid air from the first and second zones and throws it into the room.

For uniform blowing of products with heated air in the dryer, grates 2 are provided. Products are blown from top to bottom.

The set parameters of the drying air (temperature and relative humidity) are maintained by an automatic control system.

The casing of the tunnel frame consists of two layers of separate panels with sealing of the joints between them.

Each inner panel has a wooden frame, sheathed on both sides with cardboard.

The frames of the outer panels are sheathed with cardboard on the inside, and with fire-resistant paper laminated plastic on the outside. Between the shields there is a layer of filling foam.

The purpose of the pre-dryer is to quickly remove moisture from raw pasta at the stage while they have plastic properties. The main purpose of this stage is to reduce the overall drying time of the pasta.

In addition, the rapid decrease in humidity prevents the development of microbiological processes - acidification and mold formation of products.

The parameters of the drying air in the preliminary dryer, depending on the range of products to be dried, are: temperature 35 ... 45 ° С, relative humidity 65 ... 75 %.

The duration of the preliminary drying on the lines B6-LMV and B6-LMG is about 3 hours, the moisture content of the products leaving the preliminary dryer is not more than 20%.

Final dryer lineB6-LMV(fig. 32) . It is a tunnel, the skin of which is the same as that of the pre-dryer. In the tunnel, there are five comb conveyors 6, moving bastuns 12 with products along the dryer.

From one comb conveyor to another, underlying, bastuns with products are shifted using chain shifters 7.

The operation of comb conveyors is similar to their operation in a preliminary dryer. Along the length, the tunnel of the dryer is divided into three drying zones, between which there are heating chambers. Drying air in the drying chambers moves through channels 11 located on the side and on top of the chambers.

Each chamber has two centrifugal fans 2 (on one side and the other) and two sections of water heaters 5 from ribbed pipes: in the first zone - between the second and third, fourth and fifth tiers, in the second and third zones - between the first and second, third and fourth tiers.

The fans suck in the air that has passed through the products, which are placed on the fifth (lower) comb conveyor, and supply it through the side channels upward. From here, it goes to the drying chamber, blowing successively from top to bottom the products on all tiers, warming up in air heaters. Fresh air is sucked into the dryer hole 1 in the walls of the heating chambers.

The exhaust air is discharged into the room through openings 8. The dampers of openings 1 and 8 open and close automatically.

The air temperature in the drying zones, as well as in the preliminary dryer, is 35 ... 45 о С, and the relative air humidity is 70-85%.

Fig. 32 Scheme of the final dryer B6-LMV for long products

In the areas of warmth, the relative humidity of the air is close to saturation - to 100%, therefore, moisture from the surface of the products does not evaporate. In these zones, the moisture content of the product is equalized in all inner layers: a slow migration of moisture inside the products to the surface, from where the moisture was removed while the products were in the previous drying zone. At the same time, the moisture gradient inside the products decreases, and internal shear stresses are absorbed.

Thus, moisture is removed from the semi-finished product in the final dryer stepwise: the drying periods are constantly alternated with the heating periods. This is called the pulsating drying mode, resulting in durable glassy breaks.

At the end of the final dryer, two axial fans 9 are installed, which suck in air from the room, blow through the heaters 10 and create an air curtain that prevents air from entering the dryer at the exit point of bastuns with dried products.

In the lower part of the drying tunnel, there is a chain conveyor 4 for returning empty bastuns to the self-alignment of the line. To prevent condensation of vapors under the dryer, pipes 13 are laid through which hot water circulates.

The duration of the final drying of products depends on the assortment and averages 11… 12 hours on the B6-LMV line, 14… 15 hours on the B6-LMG line. Further, the products with a moisture content of about 13.5% are sent for stabilization and cooling to a tunnel-type storage stabilizer.

Final dryer lineB6-LMG. Designed for final drying of long products on the B6-LMG line. The same dryer is installed on the Braibanti line with a capacity of 24 tons / day.

This dryer differs from the final dryer B6-LMV in that it has one more drying zone and one more tempering chamber.

Batteries of water heaters are installed in the first and third drying zones under the second and fourth conveyors, and in the second and fourth zones - under the first and third conveyors.

The closer summer is, the more the desire to lose weight and put yourself in order grows. But for those who spent a long winter eating pasta, sausages and sandwiches in a hurry, it is difficult to rebuild in a new way. Most fitness trainers agree that it is impossible to eat pasta on the dryer. However, nutritionists have a different opinion.

Arguments for and against drying pasta

Opponents of pasta provide the following arguments for rejecting them:

• high glycemic index (rapidly increase blood sugar);
• the presence of gluten;
• high calorie content.

Now only diabetics and nutritionists without deep knowledge pay attention to the glycemic index. According to them, when a lot of glucose enters the bloodstream, our body, striving for a constant composition, can only utilize its excess into fat. Therefore, a high GI is evil for them. However, for such a scenario, the glycogen depots of the liver and muscles must be overfilled, which does not happen on a diet.

Gluten-free diets do not contribute to drying (but do not interfere), they are needed only for people with celiac disease.

As for the calorie content, in 100 grams of boiled pasta, buckwheat and rice, it differs by no more than 5-10 calories. It is believed that foods with a higher glycemic index will saturate for a shorter period of time, but the absorption of food and subjective hunger / satiety from it depend not only on the GI. Someone is hungry after a plate of buckwheat, and after the same, but the pasta is full. It's no problem to eat chicken pasta rather than breast-fed rice, but still keep within your daily carbs.

What pasta can you cook and how to cook them

Those who follow a diet face another danger of pasta: this product contains very few biologically active substances. On drying, the amount of food is limited, so it must have a high nutritional value, meeting the needs for vitamins and minerals as much as possible. In order not to dry out to vitamin deficiency, you should choose pasta:

• from whole grain flour (whole grains contain more B vitamins), despite their unappetizing grayish or brown color;
• with additives - tomato, spinach, buckwheat, etc.

To preserve the useful components, they need to be undercooked - served aldente.

Losing weight and drying is not at all a reason to completely abandon familiar products. Rather, it is a reason to reconsider the amount in the diet and how it is prepared.

Drying is one of the ways to preserve pasta dough, which consists of hydrophilic polymeric substances. If you do not remove moisture from it, then microbiological, biochemical and other processes will develop, which will quickly lead to spoilage of the product.

Pasta dough releases moisture extremely slowly when dried. To control the dehydration process, it is necessary to take into account the entire set of properties of the pasta dough, remembering that the main task of the drying technology is to obtain a high quality product with minimal energy and labor costs.

Drying of pasta, like drying of any other capillary-porous materials, takes place in two periods. The first is characterized by a constant rate and is due to the intensive removal of moisture, which is less strongly associated with starch. In the second period, characterized by a decreasing drying rate, the protein part of the products is dehydrated, which retains moisture more firmly than starch.

Properties of pasta as a drying object. Raw pasta is dried at a moisture content of 30-32.5%. According to the classification of P.A.Rebinder, raw pasta that has passed the stage of pressing refers to coagulation structures, which are characterized by the presence of an elastic framework formed by the forces of intermolecular adhesion of protein molecules. Such structures exhibit plasticity, elasticity and thixotropic properties. When dehydrated, coagulation structures gradually lose their plastic properties; at the same time, their elasticity increases, as a result of which the structure is strengthened, and by the end of drying they become a hard brittle body.

When dried, pasta retains its plasticity up to a certain limit, and starting from a moisture content of 25-20%, the elastic properties gradually overlap the plastic ones.

The kinetics of dehydration of pasta dough is characterized by extremely slow migration of moisture in the thickness of the product. Due to this, the change of plastic deformations by elastic ones is extremely uneven: on a dried surface, elastic deformations can reach a limiting value, while the deep layers remain plastic. The end result of structural changes during drying is a decrease in the volume and linear dimensions of the products.

Thus, during drying, the following properties are most clearly manifested in pasta dough:

linear and volumetric shrinkage, which can cause cracking and curvature of products under sparing drying modes and high irregularities in the moisture field. The ability to crack and bend products remains after drying;

low moisture conductivity, which causes the lag of internal moisture transfer from moisture return to the environment and causes the unevenness of the moisture field;

thermal denaturation of proteins and partial gelatinization of starch at high temperatures (VIS-2 dryer), leading to a decrease in strength and deterioration of the color of products;

two forms of moisture bond: adsorption and osmotic, and the adsorptively bound moisture moves in the form of vapor, the rest in the form of a liquid;

stronger moisture retention by dough proteins in comparison with hygroscopic starch due to the greater hydrophilicity of proteins. In the first period of drying, dehydration is more intensive due to the fact that starch loses moisture in the first place.

Modes of convective drying of pasta... The term “drying mode” is understood as a set of “parameters of drying air (temperature, humidity, speed), duration of drying, the presence of periods of drying and heating, their duration and frequency of alternation.

Drying modes used in the pasta industry are diverse. When choosing a mode, it is necessary to take into account the above technological properties of the pasta dough. In order to avoid distortion and cracking of the product, one should strive for its uniform drying both along the section and along the length. The ideal mode is such that the internal mass transfer of moisture will not lag behind the moisture release from the surface of the products. It is difficult to implement such a regime, since during drying, a significant moisture gradient is formed in the mass of dried products, at which the supply of moisture from the deep layers lags behind its evaporation from the surface of the product. Therefore, it is very important to maintain such a gradient value at which the drying rate would be optimal.

At the initial stage of drying, the moisture gradient is minimal, and then its value increases. It follows from this that at the first stage of drying, severe modes are possible, and at the subsequent ones - gentle ones.

With respect to pasta dough, the following rule applies: as long as it is plastic, it can be dried quickly (stresses and resulting cracking may not be observed, even if the difference in moisture content in the center and on the surface is significant).

For pasta, the most widely used two drying modes:

three-stage or pulsating mode;

continuous, with constant drying capacity of air.

In each mode, the main goal is to prevent the occurrence of high moisture gradients dangerous for cracking products.

The three-stage regime, as the name suggests, consists of three stages. First stage - pre-drying... Its purpose is to stabilize the shape of raw products, to prevent souring, mold and stretching. Drying lasts from 30 minutes to 2 hours and is carried out under relatively severe conditions. During this time, one third to one half of the moisture is removed from the amount that should be removed from the pasta. Such intensive dehydration in a relatively short time is possible only at the first stage of drying, when the pasta is still plastic and there is no danger of cracking.

The second stage is called sedation.... By increasing the relative humidity of the air, softening of the crust is achieved - moistening the surface layer, as a result of which the moisture gradient decreases and the resulting stresses are absorbed. This process is best carried out at relatively high temperatures and relative air humidity, at which the rate of diffusion of moisture increases and the duration of annealing is reduced.

Third stage - final drying- is carried out in a soft mode, since the products are in the area of ​​elastic deformations. During this period, the rate of evaporation of moisture from the surface should be commensurate with the rate of its supply from the inner layers to the outer ones. At this stage, drying usually alternates with tempering.

In some approximation, the method of drying tubular products in cassettes in non-calorifier dryers is similar to this mode. The fan is driven in a reversible manner. With the help of a time relay, the electric motor periodically reverses the rotation of the fan. Drying is carried out in a cycle: 1) forward direction of air blowing; 2) a short stop of the engine, corresponding to the stage of bridging; 3) reverse direction of blowing. The entire cycle lasts 30-40 minutes, and the duration of the entire cycle and its individual phases can be adjusted using the same time relay.

Continuous drying with a constant drying capacity of air (mode of the second type) is extremely simple in terms of regulating the parameters of the air and the process as a whole. In this mode, the parameters of the air at the inlet to the dryer remain approximately constant from the beginning to the end of drying.

A major disadvantage of this mode is that drying has to be carried out with a high drying capacity of the air. This mode can be used for products that are most resistant to deformation: short-cut and soup fillings. Drying takes place in a shorter time than long-tube; sizes are smaller. They lend themselves better to all-round blowing with air due to spillage. And nevertheless, it is desirable to dry short-cut products under a soft mode, since the structural and mechanical properties of the dough for these products remain the same.

A new way to dry pasta. The method was developed at the Moscow Technological Institute of the Food Industry by E. N. Kaloshina and G. V. Tsivtsivadze under the leadership of N. I. Nazarov. The essence of the method consists in a special preliminary preparation of these difficult-to-dry products: in the process of drying, a new simple technological operation is introduced - scalding of products with a steam-air mixture - hygrothermal treatment.

Until now, the problem of intensifying the drying of capillary-porous colloidal materials, which include pasta, was solved by increasing the drying capacity of air. For pasta, this route proved to be ineffective. The authors of the method took a different path - changing the properties of pasta as an object of drying. After hygrothermal treatment, the products are subjected to drying under a hard mode and conditioning at the end of dehydration, which ensures relaxation of internal stresses in the finished products. Hygrothermal treatment of products before drying significantly reduces the duration of drying, since it significantly changes their rheological and physicochemical properties, as a result of which the products become able to perceive severe dehydration regimes without undergoing cracking. During this treatment, two interrelated processes take place: thermal denaturation of gluten proteins and starch modification, which, under conditions of moisture deficit, does not cross the border of the first kind of gelatinization. Both processes lead to a decrease in moisture hydration by the proteins of the dough and to the strengthening of its structure.

Studies have shown that hydrothermal treatment causes a 2-fold decrease in the coefficients of linear and volumetric shrinkage and an increase in the same number of times in the coefficient of cracking (the so-called Kirpichev criterion), the strength indicators of finished products increase 2-3 times. This heat treatment, in combination with other technological methods, makes it possible to reduce the drying time of tubular products from 20-24 hours to 8-10 hours and at the same time improve the combination of biochemical and technological qualities of finished products: strength, fracture structure, color, appearance, culinary properties. The duration of cooking products was reduced by half.

hygrothermal treatment - temperature and relative humidity of the vapor-air mixture, respectively, 100 ° C and 98%; duration - 2 minutes;

drying - temperature and relative humidity of the drying agent, respectively, 60-70 ° C and 70-80%; air speed 1.0-1.5 m / s;

conditioning (stabilization) - temperature and relative humidity of the vapor-air mixture, respectively, 90-100 ° C and 98%; duration - 1 min.

Industrial drying of pasta. In domestic and foreign industry, only convective atmospheric drying of pasta is used. Devices and installations, in which "drying" is carried out, are subdivided into two groups: conveyor belts, continuously operating and periodic.

The group of non-mechanized installations consists of two types of dryers: chamber and cabinet. The latter are widespread in the USSR.

Cabinet dryers replaced chamber dryers and were the result of their development. All cabinet dryers are characterized by a small capacity, which allows drying products of the same type at a certain moment. Products to be dried are loaded into mobile trolleys, which are then fed to the drying unit. In cabinet dryers, it is possible to dry tubular products in cassettes and in a suspended state, short-cut products - in bulk; noodles and noodles - on frames and hanging - on bastuns.

There are mainly two types of cabinet dryers: without air heating and with air heating (air heaters). The former are used for drying tubular products and hanging drying, the latter for drying short-cut products. Due to the widespread introduction of continuously operating conveyor dryers, cabinet-type heaters are not currently produced in our country, but they are still in operation at factories.

As an example, Fig. 1 shows a diagram of the cabinet dryer VVP, which is still widely used in our pasta factories.

Fig. 1. Scheme of the GDP dryer:

1 - drying chamber; 2 cassettes; 3 - fan casing; 4 - bypass distribution channel; 5 - TsAGI-700 fan on the motor shaft.

The VVP dryer is made of wood: cobbled frame, plywood sheathing. The front side of the cabinet is open for loading cassettes or frames. Correct installation of cassettes or frames is ensured by limit bars. On the ceiling of the cabinet there is an electric motor (power 1 kW, rotational speed 1400 rpm) with an impeller fan 5 mounted on its shaft. The electric motor is reversible; the fan wheel is placed in a branch pipe, through which air is directed into the bypass distribution channel 4, formed by the rear wall of the cabinet and cassettes or frames with drying products. Reversal is carried out automatically every 30-60 minutes, depending on the assortment of the product to be dried.

The cabinet is designed for 190 double cassettes 500 mm long, 365 mm wide and 45 mm high. Three rows of cassettes are placed along the width of the apparatus, two in length, and 40 in height. When these devices were used for drying short-cut products, 80 frames with dimensions 1100X700X45 mm were placed in them. The capacity of the machine is 600 kg (for ready-made pasta).

The VVP dryer has a VVP-1 model that differs in size. Drying cabinet capacity 300 kg (120 cassettes). VVD dryers are usually installed in blocks of two along the front and in two rows close to the rear walls; thus, in a block of 4 cabinets. The cabinets along the front form the corridors of the drying shop, along which the free oncoming movement of loaded and empty trolleys is ensured.

Continuously operating automated dryers in the domestic and foreign pasta industry are used for drying long-tube products in a suspended state on bastuns and short-cut and stamped products on belt conveyors. The French firm Bossano produces tunnel dryers in which tubular pasta-type products are dried in rotating cassettes. Two such lines will be installed at pasta factories in the USSR.

Suspended tunnel dryers manufactured by the Rostov-on-Don Machine-Building Plant are part of the LMB, LMV and LMG production lines, which differ in the daily productivity of presses and drying plants. LMB lines have a capacity of 500 kg / h, LMG - 1000 kg / h. The LMG production line includes a drying unit, shown in the figure in the section technological scheme for the production of pasta:

chambers for preliminary (2) and final (5) drying.

The preliminary drying chamber is a tunnel made of a steel frame, sheathed with duralumin shields. A chain conveyor runs along the tunnel carrying raw bastuns. In this chamber, the moisture content of the products is reduced by 5-6%, due to which they become more elastic, do not break off and do not stretch.

After preliminary drying, the products enter the final drying chamber, consisting of a steel frame, sheathed with duralumin shields, fenced with heat-insulating gaskets. From the final drying chamber, the products are transferred by the same conveyor to the stabilizer-storage for cooling.

For drying short-cut pasta, mesh belt dryers are used. In fig. 2 shows a diagram of a dryer of this type, which belongs to atmospheric dryers with circulation of air heated directly in the drying chamber. The chamber contains four tapes with a total area of ​​80 m2. The distribution-receiving device loads the raw products onto the upper belt, with the help of which they move along the upper zone of the dryer, then they are poured onto the second belt, from the second to the third, etc. From the last, fourth, finished belts are transferred to the cooler. storage device.

The movement of the product is shown in the figure with arrows.

Each mesh belt is made of stainless steel wire with dimensions 20X200XX2000 mm and a free area of ​​about 56%.

The belts are stretched on two drums, one of which is driving, the other is tension, and are supported by rollers. The belts have an individual drive, equipped with a disk variator, which makes it possible to change their speed from 0.14 to 1 m / min, that is, more than 7 times.

There are four zones in the drying chamber - according to the number of belts. Ribbed steam heaters are located in the space between the branches of the ribbons.

The drying chamber operates under vacuum created by an exhaust pipe, the base of which ends with an exhaust hood with a section of 10x2 m at the bottom, 3x2 m at the top and 3.4 m high. recirculation of exhaust air. Air from the shop floor is sucked in through the ventilation windows of the lower zone, sequentially passes, starting from the bottom, all four zones, and before blowing the next layer of products, it is heated in heaters. From the upper zone, air is thrown out through the exhaust hood and the pipe or partially returned to the first zone for recirculation through the exhaust duct.

After reconstruction, the KSA-80 dryer serves three LPL-2M presses.

The loading of the upper belt is significant, but there is no danger of sticking and curvature of the products, since the speed of the upper belt is brought to 1600 mm / min and the air temperature in this zone is up to 58-60 ° C (instead of 45-55 ° C).

The second belt from the top is set to a speed of 830 mm / min. The decrease in speed caused an almost twofold increase in the layer thickness, but for the second zone, such an increase is not dangerous, since the products here are already dry. The third belt moves even more slowly - at a speed of 770 mm / min; the product layer reaches its maximum thickness (60-70 mm). At the same time, the air temperature rises to 68 ° C. Drying is mostly finished in this zone, the moisture content of the products is close to standard. In the fourth zone (belt speed 770 mm / min), the air temperature is maintained at 38-42 ° C.

The disadvantage of the KSA-80 dryer is the combination at its leading edge of loading raw and unloading finished products, which violates the linearity of the flow, making it dead-end.

The innovators of the Ufa Pasta Factory have changed the way the dryer is loaded. They began to load the first and second belts simultaneously (from above) with raw products. The direction of movement of the belts, except for the first from above, is reversed, due to which the production flow is leveled, the dead end is eliminated.

The speed of the first and second belts is 430 mm / min; air temperature in both zones is 58-60 ° С. Loading of belts is carried out using a simple distributor comb installed along the entire width of the upper belt with an inclination of 45 °. Getting on the teeth of the comb, the products partially fall into the gaps between them onto the first belt, and the rest slide along an inclined plane onto the second belt.

Dried products from both belts are poured onto the third branch, which moves with some advance (450 mm / min). The air temperature in the third zone is 66-68 ° С.

The fourth belt has a speed of 380 mm / min, the air temperature in the zone is 56-68 ° C. On the reconstructed line, a strict drying regime was introduced, applicable for noodles and vermicelli. Pre-drying of products at the cutting stage and their distribution in a thin layer on the first two belts allows in the first period to achieve more or less uniform drying without warping the product. At the Ufa macaroni factory, horns are produced on this line.