Molds perform many useful functions. They age and flavor cheeses. They are used in the production of soy sauce and penicillin. Molds also manufacture the citric acid used to flavor soft drinks. They can, however, be destructive.
Molds hasten food spoilage and can cause allergic and respiratory problems.
Some molds produce toxins that can be extremely harmful even in small amounts. Some toxins can survive a long time in food, and most are not destroyed by cooking. Mostly, though, molds affect the quality of food, causing discoloration, musty odors, and off-flavors. Molds can tolerate a wide range of environments, including cold temperatures like those in the refrigerator. Freezing prevents the growth of molds but will not kill those already present.