eef 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

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