Thermal Preservation Cold Processing Thermal PreservationCold Processing Chemical reactions involving enzymes or microbes are usually the cause of food spoilage. The speed at which chemical reactions occur are directly related to the temperature of the food. The chemical reaction rates roughly double for every 10* C. (18*F) increase in temperature. Types of Cold Processing: Refrigeration: Temperature should be kept below 4*C (40*F). Slows the growth of bacteria; it does not stop it. Once food reaches room temperature, bacteria will start to grow again, increasing the rate of spoilage. Freezing Temperature should be 18*C (0*F) or lower. Food will keep for several months in a frozen state. Freezing may change the texture of some foods. (When the water in the food expands, the ice crystals may cause the cells to rupture). Freezer Burn Foods should be stored in airtight packaging to avoid freezer burn. If the packaging is not airtight, moisture will evaporate from the food. Evaporated moisture will re-freeze on the packaging or the walls of the freezer. The food cannot regain the lost moisture, thus becoming tough and dry.