- How does the food dry by freeze drying?
The food is heated to the point where the water within evaporates. The food items are then quickly frozen under vacuum conditions. The freeze dried food will retain its flavor and nutrients when it is rehydrated later.
- Does freeze drying must be achieved in vacuum condition?
According to the physical principle, the sublimation of the ice below 0℃ can only happen if the pressure is below 610Pa. An atmospheric pressure is about 100000Pa, and it can be called as vacuum when the pressure is below 610Pa
- Why is heat still needed during the freeze drying?
When the ice in the frozen food sublimates to gas, heat is removed from the frozen food and the temperature is lowered. The lower the food temperature, the slower the sublimation of ice, and subsequently the longer sublimation time. To minimize the drying time and save the production cost, it is necessary to continuously supply heat during sublimation of frozen food. However, excessive heat supply can melt frozen food, so the heat should be supplied in moderation.
- Which kind of heat supply should be adopted during the freeze drying?
There are two ways to provide heat to frozen foods. One is contact heating, the food tray is directly placed on the heating plate and heated by heat conduction. The other is non-contact heating, the food tray is hung up in the air and heated by thermal radiation. The latter is more effective than the former. When the food is heated evenly, the quality of dried products is improved.
- Which kind of food can be freeze dried?
The vacuum freeze drying machine can not only freeze dry fresh meat, poultry, seafood products, fruits and vegetables, but it can also be used for the freeze drying of ginseng root, dangshen, pilose antler and other medicinal materials. Also, milk, soy milk, fruit juice and other liquid foods can be freeze dried into instant dissolving products.
- What are the features of freeze-dried food?
The freeze-dried food is produced by sublimation of water under the condition of freezing (low temperature) and vacuum, so the shape, color, taste and nutrition of freeze-dried food are basically unchanged, and the rehydration performance is excellent.
- Does the process of sublimation keep the same when the different freeze-dried food is produced?
The sublimation process mainly depends on the temperature of heating plate and food, vacuum degree and sublimation cycle. The sublimation process will not be the same for all foods as they have different properties. To achieve an optimal sublimation process, some items are experimented on with smaller equipment before they are freeze dried in large batches.