RU993694C - Method of drying cut beet - Google Patents

Abstract

METHOD FOR DRYING CUTTED BEETS by stage-by-stage blowing of its layer with heat-transfer agent with a gradual decrease in temperature from stage to stage, which can be avoided. what. In order to intensify heat and mass transfer AND improve the quality of drying, before beating, the chopped beets are subjected to hygrothermal steam treatment, after which at the first stage they are purged for 15-40 minutes to a moisture content of 30-40% with a beet layer thickness of 50-100 mm. the temperature of the coolant is 100-150 ° C and a speed of 1-6 m / s, and in the second stage the thickness of the layer is increased to 100-200 mm; it is purged for 30-60 minutes at a temperature of the coolant of 50-80 ° C and 0.5-1.5 m / s, moreover, at each of the stages, the direction of the coolant purge is repeatedly changed to the opposite. (L s

Description

about y

ABOUT)

smiling

1-

The invention relates to a technology for convective drying of edible plant materials, in particular beets, and can be used in sugar beet processing plants, as well as in vegetable drying enterprises.

Drying juicy plant materials such as chopped beets is not an easy task. On the one hand, vegetables and fruits are rather complex structural bodies, the dehydration of which is very difficult due to the danger of loss of food quality. On the other hand, such raw materials contain a large amount of water and relatively few dry substances. These two points are very difficult to relate in such a way as to achieve the smallest change in the properties of fruits and vegetables and at the same time to obtain high technical and economic indicators of the drying process. This problem remains relevant at present, despite the extensive experience in dehydration of fruits and vegetables, accumulated by the drying industry of the food industry both in our country and abroad.

A known method is the dehydration of wet plant materials, according to which vegetables or fruits cut into pieces are laid in a layer and blown with heated air. Drying is carried out in four stages, at the first of which the air temperature is maintained within 65-70 ° C for 15-60 minutes, at the second temperature is increased to 78-88 ° C and dried for at least 2 hours. At the third and fourth stages, the temperature air support within BS-TS C and 60-78 ° C, respectively. Drying is completed when the product reaches a moisture content of 5-15%.

Such a method is not very economical due to its complexity and low productivity; moreover, it does not provide a finished product of high quality.

A method for drying sliced beets, which are cooked in autoclaves before cutting, is also known. Drying is carried out in four stages for 256 minutes at an air temperature of 74 ° C in the first stage, 56 ° C in the third, and 40 ° C in the fourth, to a moisture content of 6-7%.

The main disadvantage of this method is the cooking of beets before drying. In this case, some Sugars decompose, as well as some loss of labile biologically active substances.

The closest in technical essence and the achieved result to the described method is the method of convective drying of chopped beets in

several (about stages with a gradual decrease in coolant temperature. Drying of chopped beets is carried out by blowing it with hot air, blowing it from above.

Drying is carried out in four stages for 4.2-5 hours.

The air temperature at the first stage is 75 ° C -, at W () rum 70-75 ° C, at the third 55 ° C and at the fourth 40 ° C. Of course

(residual) humidity of the finished product 6-8%.

Blowing the chopped bit on one side only prevents the use of high temperature air for drying

and; | - for the danger of material damage. The insufficient intensity of the drying process leads to a longer drying time, which negatively affects both the quality of the finished product and

economic indicators x. With a long stay of the material in the zone of elevated temperatures, it is difficult to avoid overheating of the material with the inevitable loss of part of the biologically active

substances and carbohydrates. Long drying times result in low productivity of the drying unit. This consumes a large amount of thermal energy per unit of finished product. In addition, in such a regime it is impossible to obtain the moisture content of the dried material less than 6-87 ° C, and at the indicated humidity, grinding the dried product into powder (which is the next step after drying) is significantly difficult due to its elasticity and insufficient brittleness.

The aim of the invention is to intensify the heat and mass transfer process and to improve the quality of drying.

This goal is achieved by the fact that before beating, the chopped beets are subjected to steam hygrothermal treatment, after which they are purged on the first tap for 15-40 minutes to a moisture content of 30-40% with a beet layer thickness of 50g100 mm, a heat carrier temperature of 100-150 ° C and speeds of 1-6 m / s, and in the second stage, the layer thickness is increased to 100-200

mm and it is purged for 30-60 minutes at a coolant temperature of 50-80 ° C and a speed of 0.5-1.5 m / s, moreover, at each stage, the direction of coolant purge is reversed.

Steaming sliced beets with steam provides quick and uniform heating of the material and the destruction of the cell structure. This contributes to the rapid removal of moisture, thereby accelerating the process

drying. Under the influence of steam, not only the hygrothermal processing (blanching) of the chopped beets takes place, but also the surface layer of the material is dried, which reduces its adhesion during drying in the bulk layer. In addition, during hygroscopic steam treatment, firstly, there is no contact of the material with atmospheric oxygen, as a result of which the material does not oxidize, and secondly, the oxidizing enzymes are destroyed, which virtually eliminates the oxidation of the material in subsequent stages of drying. In addition, steaming significantly reduces the loss of water-soluble vitamins and other substances. Alternating purging of the product layer with hot air from top to bottom and from bottom to top contributes to the intensification of the drying process as a result of equalization of moisture content fields and temperatures throughout the volume of dried material. This makes it possible at the initial stage to dry the material with a high-temperature coolant in a bulk layer with a thickness of 50-100 mm, and at the second stage, double the thickness of the layer and blow it with a coolant of lower temperature, which significantly accelerates the drying process and increases the productivity of the drying unit. The alternating direction of the heat carrier, in addition, protects the material being dried from overheating when it comes in contact with hot air, which results in a high quality finished product.

The thickness of the material layer, select the outcome from the following conditions. In terms of maximum productivity, it is desirable to increase the thickness of the layer as much as possible. However, in the first drying step, the maximum layer thickness is only possible up to 100 mm. With a larger thickness, the material located in the middle of the layer will remain moist. It is not rational to use a layer thickness of less than 50 mm with this method, since in this case the layer can practically be blown on one side. Drying in the first stage is carried out to a moisture content of 30-40%. When this humidity is reached, the temperature of the material begins to increase sharply, and in order to maintain its quality, it is necessary to reduce the temperature of the coolant to 50 ° C. From this moment, the second drying step begins, in which the thickness of the material layer is doubled, i.e. up to 100-200 mm, which is possible due to the fact that the main moisture from the material has already been removed. An increase in the thickness of the layer above 200 mm is unprofitable, since it increases

layer resistance, and this leads to excessive energy costs and higher cost of the finished product.

The temperature and duration of 5 drying at both stages provide for the optimal conduct of the drying process. With decreasing temperature and time, the drying process lengthens, and with an increase in one and the other, overheating of the material occurs and the destruction of biologically active substances and carbohydrates:

At the first stage of drying, when the material has a high humidity, it is necessary to supply as much hot air as possible. 5 In the first drying step, an upper air velocity limit (6 m / s) is set to prevent swelling and expansion of sliced beets. Lower limit (1 m / s) allows for purging

0 layer and supply of the minimum required amount of heat. At the second stage of drying, the air velocity is reduced to 0.5–1.5 m / s, which results in weak blowing of the material (with a generally softer drying mode). This is sufficient to remove the remaining moisture.

The method is carried out as follows. Beets, sliced into plates with a thickness of 1.5-6 mm (shavings), are laid

0 with a layer of 50-100 mm on a conveyor, the belt of which is an easily blown metal mesh; a mesh made of synthetic material. In the first zone of the conveyor, pipes are located above the grid,

5 through which steam is supplied with a pressure of 0.1 MPa and at a temperature of 100-150 C.

A condensate drain pan is located under the conveyor screen. This conveyor zone is sealed and insulated. In her

0 they carry out hygrothermal treatment by heating the chips with steam and drying their surfaces, which prevents it from sticking together, Beets are kept for 2-8 minutes depending on the conveyor speed, beet mass and

5 steam consumption.

Then, the sliced heat-treated beets are conveyed into the zone in which they are blown with air at a temperature of 100-150 ° C and a speed of 1-6 m / s from top to bottom. At

In this case, air reaches the middle of the layer, is cooled to 40-50 ° C and saturated with moisture up to 90-95%. With such air parameters, drying of the material can no longer take place. Therefore, in the next zone, the direction of flow of the coolant is reversed and the beet layer is blown upward. There may be several such zones. Such alternation of the direction of movement of the coolant is carried out in zones up to a moisture content of chips of 3040%. This is a critical content, below which the temperature of the material begins to rise sharply. This completes the first drying step. The total drying time in the first stage is 15-40 minutes.

To maintain the quality of the material at this moment, it is necessary to switch to another mode, which is carried out in the second stage by transferring the beet layer to another conveyor, on which the beets are laid in a layer 100-200 mm thick and dried at an air temperature of 50-80 ° C at a speed of 0.5 -1.5 m / s. At this stage, the direction of movement of the coolant also changes and the product layer is blown alternately; from top to bottom and from bottom to top. Drying time is 30-60 minutes.

According to the technology described above, three pilot industrial drying of chopped beets was carried out. The drying conditions for these examples are tabulated.

In all three examples, the dried chopped beets had a final moisture content of 4-5%. Such humidity ensures good dispersion of the dried beets and the production of sugar-containing powder from them, in all respects corresponding to 61 technical time conditions.

The described method has the following advantages over other known methods. The drying time is reduced from 4-5 hours to 45-100 minutes, i.e. 2-3 times. The drying (boradova) productivity increases by 2-3 times, and the production line - by 1.5-2 times. The heat consumption per unit of finished product is reduced by 1.5 times, as a result of which the efficiency of the dryer is increased and the cost is reduced.

(56) U.S. Patent Nfe 2318027, CL 34-29, published. 1940.

Dried and fruits. Collection. M .: Food industry, 1980, p. 8485.

Filonenko G.K. et al. Drying of food and plant materials. M .: Food industry, 1971. p. 330.