Drying
Control of the moisture content of food is one of the oldest preservation methods. Removal of water from the food prevents growth of most microbes and slows down enzymatic deterioration.
Water removal from food can have several forms. The oldest and most primitive method for removing water is sun drying, which requires long hot days with low humidity to dry food evenly and quickly. Over-drying and uneven drying will result in nutrient destruction, microbial growth, and other undesirable changes. Drying of food in the home can be done and a later chapter tells how.
Water activity or availability of water in foods can also be controlled by adding compounds to the food which tie up the water chemically, making it unavailable for use in an enzymatic reaction or for use by the micro-organisms. The two most common home ingredients used in this way are sugar and salt. In making fruit preserves, the high sugar content ties up the water and helps prevent growth of many micro-organisms.
Methods used for preserving food in the home are combinations of the basic techniques discussed here. Make certain the recipe you follow is from a reliable source. Follow it precisely and be assured of a safe and wholesome food supply.