ABSTRACT
Removal of water and the consequent lowering of water activity constitutes an important principle of food preservation. When removal of water is carried to essential completion resulting in food materials with water contents between 0 and 15-20%, the methods involved are called dehydration processes. In other cases only part of the water is removed, which results in concentrated solutions or dispersions or in semisolid products with water contents in excess of 20%. The methods involved are called concentration processes. The purposes of concentration can vary. It may be used as an economical preparatory step for subsequent dehydration, as in the cases of spray-dried tea or freezedried coffee. It may be used to reduce the bulk of materials to be preserved by freezing or by sterilization, as in the cases of frozen orange juice or evaporated milk. It may also be used as a method of preservation in its own right, for such food products as maple syrup, which do not deteriorate readily at the water activities achievable by concentration.
