Beef freeze dryer process

Beef freeze dryer process
Food freeze drying is a special form of food vacuum drying. There are many other methods for freeze-drying, such as vacuum freeze-drying, sublimation drying, and freeze-sublimation drying. It freezes the material below freezing point to make the water into solid ice, and then makes it at a higher vacuum. The ice is directly removed by conversion to water vapor without a liquid state, thereby obtaining a dried product. The phase equilibrium relationship of water is the basis for the research and analysis of freeze-drying of water-containing foods. It can be known from the phase equilibrium diagram of water and the three-point diagram. When the pressure is greater than 610.5Pa, the result of isothermal heating from solid ice is inevitable. It is necessary to pass the liquid state to reach the gaseous state, and when the vapor pressure around the ice is lower than 610.5 Pa, the solid ice heating can be directly sublimated into water vapor, which is the basic principle of freeze drying.
Freeze-dried foods have the following characteristics:
a. Freeze-dried foods are safely stored for a long period of time and are easy to transport because they are relatively dehydrated and can be stored safely without any preservatives.
b. Since the material is frozen to form a stable solid skeleton before sublimation and dehydration, the solid skeleton remains basically unchanged after the water is sublimated, so the dry product does not lose the original solid structure, maintains the shape of the fresh food, and has a porous structure. The product has ideal fast solubility and rapid rehydration.
c. Since the moisture in the material exists in the form of ice crystals after pre-freezing, the dissolved substances such as inorganic salts originally dissolved in water are evenly distributed in the materials, and when the ice crystals sublimate, the dissolved substances dissolved in the water are precipitated in situ. In the general drying method, the internal moisture of the material migrates to the surface, and the inorganic salt carried on the surface precipitates on the surface to cause surface hardening. Therefore, the freeze-dried food has no surface hardening problem.
d. Freeze-drying is carried out under low temperature and high vacuum, which avoids the destruction of heat-sensitive components in the food during processing and the oxidation of easily oxidizable components, so the maximum freeze-dried food
Maintains the nutritional and physiologically active ingredients of the food.
e. Due to the low rate of various chemical reactions at low temperatures, browning caused by fading, enzymes and amino acids caused by pigmentation during lyophilization hardly occurs, so freeze-dried foods do not need to add any pigments and their color remains. Bright as ever, the flavor is unchanged.
f. Freeze-dried foods are easy to absorb moisture and deliquesce, so they require high packaging materials. In addition, the porous and loose structure makes the freeze-dried foods extremely fragile and powdery during transportation and sales. Therefore, packaging materials or packaging with certain protective functions should be used. form.
  The basic steps:
Beef screening finishing → slicing → pre-freezing → sublimation drying → desorption drying → packaging → finished product.
a. Screening the spiced beef made from the semi-membrane muscle, the longest muscle on the back, etc., and remove the fat and connective tissue attached to the cooked beef. The slice thickness is 5mm, and the length and width are about 3.5-2cm. Place the cut material in the drying tray and place the probe in the material center
Pre-freezing is to lower the temperature of the wet beef slices below the eutectic point in a short time, so that all the water is frozen into ice crystals, thereby ensuring good morphology, texture and rehydration of the sublimed dried beef pieces.
High freezing rates will result in the formation of small ice crystals between cells and even the formation of intracellular ice crystals, which will affect the drying rate of the product as well as the porosity and rehydration ability of the product. Excessive freezing rate leads to a significant reduction in the rehydration capacity of the beef. The color of the product is paler before the rehydration or after rehydration, and the original color of the beef itself is lost. However, unlike raw beef lyophilization, the freezing rate does not seem to have any effect on the dehydration rate or rehydration capacity of cooked beef in a relatively wide range, and the slower the freezing rate, the quality of freeze-dried cooked beef during storage. The faster you fall. The freezing rate has a certain influence on the drying time. The ice crystals produced by quick freezing are smaller, the ice crystals produced by slow freezing are larger, the large ice crystals are good for sublimation, the small ice crystals dissolve quickly, and the smaller the ice crystals, the more the products reflect after drying. The original structure shape and performance, so the eutectic point of beef should be considered to select the optimal freezing rate, which can shorten the drying time and ensure the quality of freeze-dried beef. In the test, the shelf was cooled to -15 °C, and the material temperature was reduced to -20 °C after 1.5 h. After 0.5 h of freezing, it was considered to reach the eutectic temperature of the beef. -2 7 °C. (Beef eutectic point is around -25 °C) and kept for 1 hour. This time is completed for pre-freezing.
Effect of sublimation temperature on the quality of freeze-dried beef
The latent heat required for sublimation drying is transferred from the heat source to the surface of the dried material through the external heat transfer process, and the heating of the shelf must ensure that the material temperature is lower than the eutectic temperature so that the material does not melt, and the temperature is too low to be detrimental to the improvement of the drying rate. As the temperature of the external gas rises, the surface temperature of the dried layer also increases. Therefore, the drying rate can be increased by increasing the gas temperature, but it is limited by the following conditions:
a) the temperature of the frozen portion of the product is lower than the temperature at which the product is co-melting;
b) the temperature of the product drying layer must be lower than the disintegration temperature or the maximum temperature allowed;
c) Maximum shelf temperature. Increasing the temperature of the gas When it is limited by the maximum temperature that the drying layer can withstand, in order to increase the drying rate, the thermal conductivity of the dried layer must be increased. When the melting temperature of the frozen layer is limited, in order to increase the drying rate, it is necessary to increase the drying rate. The average effective diffusion coefficient of the layer. The thermal conductivity and diffusion coefficient of the dried layer are all related to pressure. In the test, the shelf temperature is 55 °C, and the surface temperature of the beef during the sublimation drying process should not exceed 40 °C to prevent thermal denaturation of the protein and affect the rehydration of the product.
Summarize the lyophilization process conditions of cooked beef:
The pre-freezing time is 3h, the pre-freezing end temperature is -30°C, and the drying chamber vacuum is 60Pa.
The water trap vacuum is 45 Pa, the water trap temperature is -40 to -50 ° C, and the drying time is 6-8 h.
The appearance of freeze-dried cooked beef has a dark red color and no difference before lyophilization, and the surface is focally shaped to give the product a special flavor. The lyophilized cooked beef is rehydrated in normal temperature water at 20 ° C, and the product is restored to the state of fresh cooked beef before lyophilization in about 1 minute. After rehydration, the product has good quality and the taste is basically the same as before lyophilization.