SU935065A2 - Method of producing concentrated liquid food products - Google Patents

Description

(5) METHOD FOR PRODUCING CONCENTRATED LIQUID FOOD PRODUCTS

one

The invention relates to a technique for concentrating liquid food products by freezing part of the solvent, mainly for the food industry, and can be used in medicine and the chemical industry to produce concentrated thermolabile products, as well as for desalinating seawater.

According to the main auth. N ° 685271, a process for the preparation of concentrated liquid food products is known, which involves freezing moisture in the form of ice on a cooled surface and the subsequent melting of ice. To obtain a solution of a given concentration, two, three, and multistage freezing are used 1.

However, with the existing method, there is a large loss of dissolved substances with removable ice. As studies have shown, to maintain crystal formation throughout the entire freezing cycle, it is necessary at the initial moment of the process to maintain a significant temperature difference dT between the concentrated solution Tp and the cooled surface, i.e. start the process at a temperature on the surface T (at lO-lS C below the equilibrium for a solution of a given concentration.

10 This leads to the fact that the growth rate of crystals at the initial moment considerably exceeds the rate of removal of the concentrated solution from the interface. Period from

ts maximum dT is characterized by intense freezing of ice, however, this results in an enhanced capture of solute by an intercrystalline structure, and this causes a large loss of solute with removable ice. As the ice layer increases, its thermal resistance R increases, aT decreases, the temperature difference decreases the crystallization rate, approaching the rate at which the concentrate is removed from the interfacial surface, thereby excluding the possibility of the crystal structure trapping solutes. However, the total loss of dissolved substances with removable ice is large. As a result of the growth of thermal resistance, further process leads to equal temperatures of the freezing surface and the solution and the crystallization process ceases. Moreover, the result is an increase in the concentration of the solution due to the freezing of part of the solvent: a more concentrated solution requires lower temperatures The aim of the invention is to reduce the loss of solutes with removable ice by equalizing the rate of advance of the crystallization front. and the rate of removal from the phase separation of the solution of high concentration. The goal is achieved by the fact that according to the method of producing concentrated liquid food products in the process of freezing moisture, the temperature of the cooled surface is continuously lowered, ensuring a constant temperature difference between the product being concentrated and the freezing surface in. Otherwise In other words, the process is carried out at a constant driving force of the process, i.e., with the optimum temperature difference dT between the concentrated thief and freezing surface providing equality crystallization rate and removal rate from the phase boundary. A constant temperature difference is maintained by continuously lowering the temperature of the cooled freezing surface with allowance for the increase in ice thickness. The process ends after a solution of the desired concentration is obtained. Example. The pre-cooled to-temperature block juice with a solids content of 11.4% flows into an intermediate tank, from which it is fed by a circulation pump to the crystallizer. The temperature of the onset of crystallization for juice with such a concentration is 9 4 minus 1.3 ° C. In order to minimize the loss of solutes, it is necessary to maintain an optimum temperature difference between the concentrated solution and the freezing surface T-2-3 C. Thus, in the first freezing stage it is advisable to set the freezing surface temperature to -1, 3-2, 8 ° C. After the maximum amount of ice has formed on the surface of the frosting, the time of the second freezing stage comes: the freezer contains a concentrated solution 29, the crystallization temperature of which according to the schedule is minus 3.8 ° C. Taking into account the losses caused by thermal resistance of the layer, and taking into account the optimum temperature difference between the solution and the freezing surface, it is necessary to lower the freezing surface temperature Tn -3.8-2, 5-1, 8c, etc. The concentration process may contain from two or more freezing stages. After obtaining a solution of the required concentration, the chilling ice surface is removed from the crystallizer, leaving a concentrated solution in it. The drawing shows the dependence of the freezing temperature of the solution on the concentration of solids. For a perfect introduction of the process, it is necessary to drive it directly along the curve. If the process is carried out in one step, then in order to achieve the concentration of the kS solution, it is necessary to set the temperature on the freezing surface at minus 7.8 ° C. The magnitude of the losses in this case is proportional to the area ABC. If the process consists of two steps and goes through the AD-DE-EK-KS line, then the amount of dry matter loss with ice is proportional to the area of ADE + TSA. As can be seen from the graph, the area of ABC is much larger than the area of ADE + TSA. Consequently, the amount of dry matter loss during two-stage freezing is reduced by about 2 times. To achieve a higher concentration, a three-step or more freezing can be applied. To achieve a solution concentration of 0-501 while maintaining the temperature difference between the concentrated solution and the freezing surface less than 1 ° C, multi-stage freezing is necessary (about 10 steps), which causes operational difficulties increases the complexity of process control. On the other hand, with a temperature difference of over C, the loss of solids with ice removal significantly increases. The optimal number of freezing stages is from two to four stages, which corresponds to the temperature difference in (,

With a continuous decrease in temperature, which ensures a constant temperature difference between the concentrated solution and the freezing surface, the capacity of the installation increases by 15-25%, and the value of losses, dissolved losses with removable ice, decreases by 25-30 0

Claims (1)

1. USSR author's certificate No. 685271, cl. A 23 L 3/00, 1978.