Related Reads: Conventional Drying Of Fruits and Vegetables Freeze Drying Process Freeze drying causes very little change in chemical components of food.There is very minute difference in the nutritive value of fresh food and freeze dried food product.There is very good retention of volatile flavour and aroma components with the process.The moisture content of freeze dried food product is below 3%.Freeze dried product is lighter in volume/weight.Phase Diagram Of Water Showing Sublimation Of Ice | Source -Properties Of Freeze Dried Food Products

Food products are dried in 2 stages: first by sublimation to 15% moisture content and then by evaporative drying (desorption) of unfrozen water to 2% moisture content.The rate of drying depends on resistance of the food to heat transfer and to a lesser extent on resistance to vapor flow from sublimation. The water vapor pressure of a food is held below 4.58 torr (610.5 Pa) and water is frozen.When the food is heated solid ice sublimes into vapor without melting.The pressure in food dried cabinet is below the vapor pressure at the surface of ice and a vacuum pump is present in the cabinet which removes the vapor and let it condense on refrigeration coils. Lyophilisation or freeze drying is a process in which water is frozen followed by its removal from the sample initially by sublimation(primary drying) and then by sublimation(desorption).Since heat is not applied in this case.So,both nutritional qualities and sensory characteristics were better retained.Freeze drying has similar preservative effect by reduction in water activity without heat application. Freeze Drying Process | Freeze Drying Definition

Freeze dried food