Freeze drying
Certain products cannot be stored in liquid form for the considerable time and should be reduced to a dry powder, which can then be stored on a cold or ambient temperatures. Water must be removed to make them powders, but any heating above the boiling point of water will cause rapid wear. Water must therefore be removed at low temperature, requiring low pressures of about 125 PA.
The process is carried out in a vacuum chamber with a refrigerated contact freeze plate, heaters and vacuum pump. Between the camera and the pump can be refrigerated separator to prevent too much water the pump inlet. The product is filled into containers on the plates and frozen down to about 25C, depending on the product, but sometimes as low as 50C. vacuum and, at the same time, a carefully controlled amount of heat is then applied, to ensure the latent heat of sublimation (ice and vapor), not allowing the temperature to rise.
As the water is driven off, the product turns into a dry powder. It is extremely hygroscopic and must be Packed in sealed containers as soon as possible after the completion of the cycle. This process was developed for the preservation of antibiotics, but is now widely used for the manufacture of other products (such as 'instant coffee, tea, soup and other
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Food refrigeration and freezing