RU2736112C1 - Method for dry black tea treatment - Google Patents

Abstract

FIELD: tea industry.

SUBSTANCE: tea leaves wilting to moisture content of 75–65 %, twisting, fermentation and drying till residual moisture content is less than 10 %. Secondary drying is carried out by means of thermal exposure to UHF electromagnetic field in drying chamber for 8–12 min with constant pressure in drying chamber, selected from the range of values of 50–60 kPa. Dry black tea is heated to 70.0–80.0 °C. Rate of temperature growth in drying chamber under action of electromagnetic microwave field is selected from range of values of 1.0–3.0 °C/s. After achieving the specified temperature value and after the thermal action time termination, the thermal exposure to the electromagnetic microwave field with simultaneous transition into pressure reduction mode in chamber to a value selected from range from 14 kPa to 4 kPa. Dry black tea is held in the chamber at decreasing pressure until its temperature drops to the temperature of the production room, in which drying chamber is installed.

EFFECT: invention ensures preservation of maximum quantity of useful substances in dry black tea: up to 60 % of vitamins, up to 40 % of alkaloids, up to 50 % of proteins and amino acids, organoleptic properties, with simultaneous reduction of microbial load on dry black tea.

1 cl, 3 ex

Description

Technology area

The invention relates to methods for processing tea, and in particular to methods with double drying, in which the second drying of the tea takes place using microwave radiation.

State of the art

Currently, a large number of methods for processing black tea, dry tea raw materials are known.

Traditional technology of black tea production (USSR author's certificate No. 396105 "Method for the production of black long tea", published 01.01.1973) D1, includes the following stages of processing the collected green tea leaves: withering, rolling, fermentation and drying. The operations of withering, rolling, fermentation and drying are carried out as follows: fresh green leaves of the Camellia sinensis plant wither (undergo soft drying), grind, ferment (in this process, the enzymes in the tea leaf use atmospheric oxygen to oxidize various substrates to obtain brown products), and then fire-dried (to dry the tea leaves).

In the production of black tea, maceration is required to release the fermented enzymes and their substrates in the leaves. There are two main mechanized methods of maceration: the first, which involves passing pre-weighed batches of heavily wilted tea leaves through rolls before the stages of fermentation, fire drying and drying, in which tea resembling dry leaves is obtained, and the second - using CTC machines (from the words "cut -tear-cure "-" cutting-breaking-twisting "), in which a tea is obtained, which quickly infuses and gives a strongly colored infusion. Both rolls and CTC rolls are often used in combination with a rotary vane machine, which is an extruder type machine and is used to pre-condition (squeeze / crush) the leaves before maceration. Examples of such methods are disclosed in the RF patent No. 2470519 for the invention "Production of black tea" (D2), published on December 27, 2012, USSR author's certificate No. 1600668 "Method for the production of black long tea" (D3), published on October 23, 1990, USSR author's certificate No. 1669418 "Method for the production of black long tea" (D4), published on August 15, 1991, USSR inventor's certificate No. 625678 "Method for drying tea" (D5), published on 09/30/1978. In the withering process, the purpose of which is to dehydrate the tea leaf, the leaf loses up to 55% moisture. Tea withering can be natural or artificial. Natural withering lasts 10 to 24 hours and usually occurs in the shade, under awnings or in well-ventilated areas, although some teas can wither in the sun. Artificial withering occurs with the use of adsorbents and heated dry air blowing in special dryers and lasts from 2 to 8 hours. In addition to moisture loss during the withering process, the leaf, along with moisture, loses cellular turgor (pressure), as a result of which the leaves become more elastic, which makes it possible to obtain high-quality rolled leaves, the juice of the tea leaves becomes more viscous and thick, which, in turn, increases the quality of fermentation.

The task of the rolling operation is to destroy the veins of the tea leaf and release the enzymatic enzymes and their substrates in it. During rolling, cells are destroyed, the flowing cell sap envelops the surface of the leaf. Later, when brewing tea, the juice squeezed out of the cells and dried on the surface of the leaf dissolves easily, while the cell juice dried in undisturbed cells (i.e., non-leaked juice) dissolves worse.

The fermentation process is a complex biochemical process in which a mixture of tea polyphenols is oxidized in the presence of tea enzymes (enzymes) that activate this process. As a result, theaflavins are formed, which give the tea infusion freshness and brightness, and thearubigins, which give it strength, richness and a characteristic red-brown color. Oxidation can occur spontaneously: unprotected cells on a cut of plant material absorb oxygen, soften and change color, if this process is not stopped, the product will dry out or rot, depending on atmospheric conditions. There is a spontaneous oxidation stage in the tea production process, but the main part of this process is controlled. Traditionally, this part of the process consists of laying withered tea on tables, trays, etc. for a time of about 1-4 hours in a room with humid and oxygenated air. The ambient temperature should be at least 15-20 ° C (at a lower temperature, the fermentation process stops), but also not higher than 25-28 ° C, otherwise the fermentation process gets out of control.

The final stage of traditional methods of black tea production is drying. As a result of drying, dry tea raw materials should be obtained, containing no more than 3-7% (in green tea -5%) water.

Until the end of the 19th century, tea was dried over an open fire in pans, grates, etc., hence one of the names of this stage of production - roasting. Then they began to use closed ovens with air blowing at a temperature of about 92-95 ° C, while the temperature of tea reaches 70-75 ° C.

In connection with the last stage of tea processing, two problems arise: non-compliance with the requirements for the moisture content in tea at the end of drying can lead to mold in the tea and, conversely, exceeding the drying temperature of the required values leads to a deterioration in the quality of tea, due to the destruction of enzymes under the influence of high temperature.

Dry tea is a colloidal-capillary-porous body with two main physical properties - extractiveness and hygroscopicity. The first of these allows you to consume tea as a drink. The second property makes it difficult to store tea, facilitates its spoilage. When the humidity rises above 10%, the tea starts to deteriorate, i.e. loses its aroma and taste. With a further increase to 12-14% of the moisture content of dry tea, it begins to grow moldy, and the occurrence of mold in minimal quantities is enough for the entire batch to be spoiled, since the musty smell will spread to the entire batch of tea.

The presence of mold in tea leads to a loss of condition and not only due to the deterioration of its organoleptic properties. Waste products of molds of several species of the genus Aspergillus (Aspergillus clavatus, Aspergillus parasitusn, etc.) are deadly toxins - aflatoxins.

In India's tea factories in the 70s of the 20th century, one-time drying was carried out everywhere, while in most tea-consuming countries, short-term heat treatment of dry tea was carried out as a preventive measure against the appearance of mold. In the former USSR, in order to reduce the cost of processing tea, Georgian tea was dried using the "Indian" single drying method. After a sharply increased percentage of tea rejects, it was decided after drying to perform additional accelerated heat treatment of semi-finished tea in a special heat chamber at an air temperature of 40-45 ° C and humidity of 50-65%.

Reheating to prevent the development of mold in tea is now widespread. In particular, the Hyleys Tea Company on its website describes the double-drying technology used in the production of black tea: first, the tea leaf is dried at a temperature of 90-95 ° C, and re-drying is carried out at a temperature of 82-87 ° C. Drying is carried out on baking sheets. This method of heat treatment has a number of disadvantages associated with the prolonged influence of high temperatures on tea raw materials, which leads to the fact that tea loses its beneficial properties for humans. In particular, with prolonged exposure to temperatures above 80 ° C, vitamins (A, B, C, D, E, P, PP, K), alkaloids (in particular, theine), proteins and amino acids contained in the tea leaf are destroyed.

So in the prior art, there is a known method for processing black tea, dry tea raw materials (patent RU 2683474, published 03/28/2019) D6, including carrying out, after the operations of wilting the tea leaf to a moisture content of 75-65%, twisting the tea leaf, fermentation and drying to a residual moisture content of 3- 7%, also additional drying, while at the stage of additional drying dry black tea, dry tea raw materials are thermally exposed to an electromagnetic microwave field in a drying chamber with constant pressure, while thermal exposure to an electromagnetic microwave field is carried out before heating dry black tea, dry tea raw materials to a temperature selected depending on the residual moisture content of the tea leaf after drying, while the rate of temperature rise in the drying chamber is selected from the range of 1.0 ° C / s - 3.0 ° C / s, based on the need to reduce the microbial load by dry black tea, dry tea raw materials, after reaching the set temperature, the thermal effect is stopped due to the microwave electromagnetic field with a simultaneous transition to the mode of decreasing the pressure in the chamber to a value selected from the range from 14 kPa to 4 kPa and keeping dry black tea, dry tea raw materials in the chamber at a decreasing pressure until its temperature decreases to the temperature of the production room, in which has a drying chamber.

The disadvantage of this method is the long exposure to high temperatures on black tea, which leads to a deterioration in the properties of tea raw materials. In particular, with prolonged exposure to temperatures above 80 ° C, vitamins (A, B, C, D, E, P, PP, K), alkaloids (in particular, theine), proteins and amino acids contained in the tea leaf are destroyed.

The source of information D6 was chosen as the closest analogue to the declared solution.

Disclosure of the invention.

The problem to which the claimed invention is directed is to develop a method for processing dry black tea, which will eliminate the disadvantages of the prior art.

The technical result to be achieved by the present invention is to preserve the maximum amount of nutrients in dry black tea, organoleptic properties, while reducing the microbial load on dry black tea.

The specified technical result, to which the claimed technical solution is aimed, is achieved due to the fact that the method for processing dry black tea, including the steps of wilting the tea leaf to a moisture content of 75-65%, rolling the tea leaf, fermentation, drying to a residual moisture content of less than 10%, and secondary drying by thermal exposure to a microwave electromagnetic field in a constant pressure drying chamber, while thermal exposure to a microwave electromagnetic field is carried out until dry black tea is heated to the required temperature, while the rate of temperature rise in the drying chamber when exposed to a microwave electromagnetic field is selected from the range of values 1 , 0 ° С / s - 3.0 ° С / s, after reaching the set temperature value and the end of the thermal exposure time, the thermal exposure to the microwave electromagnetic field is terminated with a simultaneous transition to the mode of decreasing the pressure in the chamber to a value selected from the range from 14 kPa to 4 kPa and soak drying dry black tea in a chamber at a decreasing pressure until its temperature decreases to the temperature of the production room in which the drying chamber is installed, characterized in that at the stage of secondary drying by means of thermal exposure to a microwave electromagnetic field, the time interval of thermal exposure to a microwave electromagnetic field is from 8 to 12 minutes, with a constant pressure in the drying chamber selected from the range of values of 50-60 kPa, and the heating of dry tea raw material is carried out to a temperature of 70.0 ° C - 80.0 ° C.

Implementation of the invention.

The temperature ranges at which dry tea, tea raw materials undergo heat treatment in an evacuated drying chamber equipped with microwave radiation sources (usually magnetrons) should be selected based on the considerations set out above.

A method for processing dry black tea, which includes the stages at which the tea leaves are wilted to a moisture content of 75-65%, the tea leaf is rolled, fermented, dried in a drying chamber to a residual moisture content of less than 10%, and secondary drying by thermal exposure to a microwave electromagnetic field in a drying chamber with constant pressure, while the thermal effect of the microwave electromagnetic field is carried out until the dry black tea is heated to a temperature, while the rate of temperature rise in the drying chamber when exposed to the microwave electromagnetic field is selected from the range of 1.0 ° C / s - 3.0 ° C / s, after reaching the set temperature and the end of the thermal exposure time, the thermal exposure to the microwave electromagnetic field is terminated with a simultaneous transition to the mode of decreasing the pressure in the chamber to a value selected from the range from 14 kPa to 4 kPa and keeping dry black tea in the chamber at a decreasing pressure until its temperature decreases to temperature of the production room in which the drying chamber is installed. At the stage of secondary drying by means of thermal exposure to a microwave electromagnetic field, the time interval of thermal exposure to a microwave electromagnetic field is from 8 to 12 minutes, with a constant pressure in the drying chamber selected from the range of values of 50-60 kPa, and the dry tea raw material is heated to a temperature of 70, 0 ° C - 80.0 ° C.

In the drying chamber, before applying a thermal effect to the drying object, a pressure is created using a pump, the value of which is selected from the range of 50-60 kPa.

Pressure values in the range of 50-60 kPa correspond to pressures located near the middle of the low vacuum range. Reducing the pressure in the drying chamber at the stage of temperature exposure is due to the need to reduce the intensity of insemination of mold, to reduce the rate of division of bacteria, i.e. to slow down the processes that, for both mesophilic and thermophilic bacteria, are intensified at the initial stage of the temperature rise in the drying chamber. The intensity of the oxidation process of tea in the drying chamber at the initial stage of thermal exposure is also reduced due to the reduced pressure created in the chamber.

The temperature effect of the microwave electromagnetic field on dry tea, dry tea raw materials is carried out until the temperature in the chamber, in the bed subjected to additional drying of tea, tea raw materials, reaches 70.0 ° C - 80.0 ° C. The specific value of the temperature, upon reaching which the temperature effect is terminated by turning off the sources of the microwave electromagnetic field, is selected based on the residual moisture content of tea, tea raw materials supplied to the drying chamber for secondary drying. These parameters affect the properties of the resulting product, because when heating black tea with residual moisture, it is important to exclude heating to the boiling point of water. When the boiling point is reached, the water from the tea, due to the vaporization process, evaporates at a high speed, simultaneously capturing aromatic compounds with it, which affect the original quality of black tea. At this stage, the pressure in the drying chamber is constant, the temperature rises at a rate selected from the range of 1.0 ° C / sec-3.0 ° C / sec, the specific speed value and the end of the thermal exposure time is selected based on the specified microbial load: speed temperature rise allows to reduce the time of passage of the phase of maximum growth of harmful bacteria, the number of which, at the end of the additional drying stage, must reach the values allowed by the current standards, norms set by the authorized health authorities, state control, etc.

After reaching the set temperature and the end of the thermal exposure time, the thermal exposure to the microwave electromagnetic field is stopped (the sources of electromagnetic radiation, which can be used as magnetrons, are turned off). Simultaneously with switching off the sources of electromagnetic radiation, a vacuum pump is turned on in the drying chamber.

After the temperature change mode in the drying chamber goes into passive, i.e. the temperature in the drying chamber, in the layer of dry tea, dry tea raw materials will begin to fall, tending to the temperature value in the production room in which the drying chamber is installed, the pressure change will occur in an active mode. The rate of pressure decrease will be selected based on the need to synchronize the processes of pressure and temperature decrease so that the current temperature value corresponds to the pressure value in the drying chamber, at which vaporization processes occur in tea, tea raw materials.

The pressure in the drying chamber at the end of the secondary heat treatment is reduced by means of a pump.

Thermal treatment of dry black tea, tea raw materials, therefore, consists in an active change in the temperature regime (with an increase in temperature at a constant rate due to the operation of sources of an electromagnetic microwave field) at a constant pressure in the drying chamber, and then - with a decreasing pressure (due to the work pump) pressure and at a decreasing temperature of dry black tea, dry tea raw materials. In this case, the pressure value with increasing temperature is maintained in the region of the middle of the interval of the boundary values of the lower vacuum, and in the mode of falling temperature with the microwave radiation sources turned off, the pressure decreases towards the values limiting the lower vacuum from the average. The temperature drops to the temperatures in the production room where the drying chamber is installed.

If in the mode of active temperature change, the task of reducing the microbial load (mold fungi and bacteria) to the required values is solved, then in the mode of "passive" temperature change, accompanied by a decrease in pressure, the process of steam formation in the water molecules remaining in dry tea is intensified. Steam molecules destroy the molecules of the tea leaf, bringing out aromatic essential oils from its deep layers. Essential oils settle on the surface of the leaf and firmly "stick" to it and retain their properties for a long time, being extracted only under the influence of boiling water at the time of brewing. At the same time, due to the short-term exposure to high temperature and the main time of exposure to temperature with decreasing values, the destruction of vitamins, organic acids does not occur in the tea leaf, i.e., after fermentation and drying, after fermentation and drying, the secondary drying mode with heating of dry tea, dry tea raw materials using microwave radiation and a subsequent decrease in temperature against the background of falling pressure, it is possible to avoid a decrease in the quality of tea.

Moreover, experiments show that due to the effect of a temperature shock and a subsequent drop in temperature under conditions of falling pressure, the process of formation of additional theaflavins and thearubigins occurs.

The short-term exposure to high temperature and the decrease in temperature, excluding the possibility of smoldering the tea leaf after exposure to high temperature, exclude the appearance of a roasted taste and / or aroma in dry black tea, tea raw materials. Temperature shock, caused first by a short-term increase in temperature, and then by its decrease, ensures the safety of vitamins (A, B, C, D, E, P, PP, K), alkaloids (in particular, theine), proteins and amino acids contained in tea sheet.

During experimental studies, it was found that exposure to temperatures from 70 ° C to 80 ° C for 8-12 minutes allows you to save up to 60% of vitamins, up to 40% of alkaloids, up to 50% of proteins and amino acids.

Examples of implementation of the claimed method.

Secondary heat treatment of dry black tea, dry tea raw materials in a drying device using microwave field generators gives the following results.

For dry black tea samples with a mold content of 2500 CFU / g at a heating rate of 1 ° C / s, the mold content varied as follows:

Example 1. The mold content of dry black tea for a batch weighing 100 g, microwave exposure time of 8 minutes and heating the samples to a temperature of 80 ° C reduces the amount of mold on the samples by 70%.

Example 2. By increasing the exposure time to 10 minutes and heating to 75 ° C, the mold content of dry black tea for a batch weighing 100 g reduces the amount of mold on the samples by 80%.

Example 3. With an exposure time of 12 minutes and heating to 70 ° C, the mold content of dry black tea for a batch weighing 100 g was reduced to 250 CFU / g.

As shown by the data of the experiments, the use of the process of heating raw materials by means of microwave technology allows reducing the number of bacteria and molds by 10,000 times within 8-12 minutes. It should be noted that the number of molds 10 ⁵ refers already to the visible range of molds, which is not allowed in food production. Accordingly, it cannot be detected at the secondary drying stage due to the fact that the raw material has already undergone thermal treatment.

It was experimentally found that the combination of temperature (from 70 ° C to 80 ° C), exposure time (from 8 to 12 minutes) and pressure (from 50 to 60 kPa) specified in this application provide maximum preservation of the beneficial properties of black tea, with this, the number of pathogenic microorganisms and molds is within acceptable values.

The importance of the temperature gradient for the destruction of microorganisms (molds, bacteria) is explained by the following reasons.

There are two widespread methods of food disinfection: pasteurization and sterilization. Pasteurization includes a single heating to a temperature of 60 ° C with further exposure at this temperature for 60 minutes or heating to 70-80 ° C with exposure for 30 minutes or heating to 98 ° C and above with exposure for several seconds. Sterilization is carried out by chemical methods and physical methods, the latter include exposure to high temperatures on sterilized objects (heat sterilization), as well as exposure to ultraviolet radiation, high-frequency currents, ultrasonic vibrations, radioactive radiation, infrared rays, etc.

As a result of pasteurization, vegetative forms of microorganisms die, but the spores survive and, when favorable conditions occur, intensive reproduction begins.

The use of high temperature during sterilization for a long time helps to completely destroy not only the microorganisms themselves, but also their spores. But prolonged exposure to high temperatures destroys the substances that give tea beneficial properties.

Therefore, the task of disinfection due to heating is the rapid passage of temperature values at which the growth rate of microorganisms (the number of generations per hour), and, accordingly, the intensity of reproduction, is maximum and the transition to those temperatures at which the growth rate is zero. At the same time, it is necessary to exclude prolonged exposure to high temperatures, which has a destructive effect on the vitamins contained in tea, tea raw materials, as well as on substances that give the taste and aroma of tea.

Microbial organisms, of which tea mold mostly consists, are predominantly mesophilic. The temperature of their growth lies in the range of + 15 ° C to 48 ° C, while the maximum value of the growth rate constant is 0.4 g / h and is reached at a temperature of about 45 ° C.

For thermophilic microbial organisms, also present in tea mold, the growth temperature lies in the range of + 45 ° C to 80 ° C, while the maximum value of the growth rate constant is slightly more than 0.5 g / h and is reached at a temperature of about 73 ° C.

The creation of a thermal effect by a microwave electromagnetic field operating at resonant absorption frequencies for water allows you to effectively evaporate moisture from dry tea, from tea raw materials, thereby reducing the growth of fungal colonies, in particular fungi from the genera Penicillium and Aspergillus, which have the ability to grow on barely moistened substrates ...

Claims (1)

A method for processing dry black tea, including the steps of wilting the tea leaf to a moisture content of 75-65%, rolling the tea leaf, fermentation, drying to a residual moisture content of less than 10% and secondary drying by thermal exposure to a microwave electromagnetic field in a constant pressure drying chamber, with thermal exposure to the microwave electromagnetic field is carried out until dry black tea is heated to a temperature selected depending on the residual moisture content of the tea leaf after drying, while the rate of temperature rise in the drying chamber when exposed to the microwave electromagnetic field is selected from the range of values 1.0-3.0 ° С / s, after reaching the set temperature and at the end of the thermal exposure time, the thermal exposure to the microwave electromagnetic field is stopped with a simultaneous transition to the mode of reducing the pressure in the chamber to a value selected from the range from 14 kPa to 4 kPa, and keeping dry black tea in the chamber with decreasing pressure to mind Reducing its temperature to the temperature of the production room in which the drying chamber is installed, characterized by the fact that at the stage of secondary drying by means of thermal exposure to an electromagnetic microwave field, the time interval for thermal exposure to an electromagnetic microwave field is from 8 to 12 minutes with a constant pressure in the drying chamber selected from the range of values is 50-60 kPa, and the heating of dry tea raw materials is carried out to a temperature of 70.0-80.0 ° C.