Protection of Foods by Drying

The preservation of foods by drying is based on the fact that microorganisms and enzymes need water in order to be active. In preserving foods by this method, one seeks to lower the moisture content to a point where the activities of food-spoilage and food-poisoning microorganisms are inhibited. Dried, desiccated, or low-moisture (LM) foods are those that generally do not contain more than 25% moisture and have a water activity (a_w) between 0.00 and 0.60. These are the traditional dried foods. Freeze-dried foods are also in this category. Another category of shelf-stable foods are those that contain between 15% and 50% moisture and an a_w between 0.60 and 0.85. These are the intermediate-moisture (IM) foods. Some of the microbiological aspects of IM and LM foods are dealt with in this chapter.