Freezing will not improve inferior foods. If the food is fresh, of top quality, and frozen using proper procedures, the effect on quality will be minimized as long as the food remains solidly frozen at a constant temperature at or below 0 degrees F. While freezing keeps many foods almost like fresh, certain changes occur.
Water in foods form ice crystals which will break down the cell structure of some foods. This affects the texture and causes mushiness. It is more likely to happen when food is frozen slowly at temperatures between 15 and 25 degrees F., like in the freezer section of the refrigerator, or when food partially defrosts and then refreezes. Texture depends on water content, fragility, and treatment of the food before and during freezing. Blanching and using syrup help protect the texture of some foods.
If frozen food is not stored in moisture-vapor-proof materials it may lose moisture and develop a dried surface condition, e.g. freezer burn. Oxygen in the air may cause flavor and color changes if food is improperly wrapped. Pack foods to exclude as much air as possible. Protect certain fruits from browning by adding ascorbic acid. Sugar, syrup, or fruit juice protects fruit from air. Soup or sauce can be used to protect cooked meats.
Foods will lose quality if stored too long or if stored at temperatures above 0 degrees F. For each 5 degrees F increase in temperature above 0 degrees F., keeping time for best quality decreases by half.