Fight Spoilage & Keep Foods Fresh Longer! Part 2
Over time, many more methods of food preservation have been developed. Once people learned why foods spoiled, it became easier for them to devise methods to guard against spoilage. People recognized that the constituents of some foods provided natural advantages for preservation. Thus, by combining these substances with other, more perishable foods, they could help preserve them as well. For example, the acidity in vinegar is at a high enough level to protect against microbial spoilage. Thus, vinegar is often added to other foods to aid in their preservation.
The act of cooking, in addition to making food more palatable, kills microorganisms that cause food spoilage and food poisoning. Cooking and blanching also inactivate enzymes that affect food quality. A particular heat treatment is defined in terms of the length of time a food is heated at a specific temperature. The heat treatment required for the destruction of microorganisms and enzymes depends on the type of food, the microorganisms of concern, the method of heating, and the intended means of storage.
Although cooking is a means of food preservation, it is typically used along with other methods to result in a food that will keep. Cooked food must be packaged or stored in a way that prevents further spoilage. For example, a steak which is cooked and then left to sit on the table will quickly be unfit to eat. But, if that cooked steak is enclosed in some container and then placed in the refrigerator or freezer, it will last a while longer. Cooked foods need to be canned, bottled, or packaged and then stored appropriately if they are not eaten right away.
In canning, cans are first filled with foods and then lidded and sealed. The cans are then subjected to a heat treatment that results in the destruction of microorganisms. The process also destroys enzymes and encloses the food, protecting it against the environment. Thus, canned foods are shelf stable. That is, they do not require cold storage. More recently, methods of aseptic packaging have been developed. In aseptic packaging, food is heat processed first and subsequently filled into plastic containers and sealed, without being contaminated.
Refrigeration and freezing assist in food preservation by slowing chemical reactions within food and inhibiting microbial growth. Generally, the colder the storage temperature, the longer a food will last. However, even frozen food won't last forever. A steak kept in the freezer for two years may not make you sick, but it will not be the same as a fresh one. Chemical and physical reactions continue in frozen foods, although at a slower pace. These reactions cause changes in the texture, flavor, and aroma of food.
Microorganisms are not capable of growth in frozen foods but they can survive in them. Under refrigeration, the growth of some microorganisms, especially those that cause illness, is prevented. However, others can grow slowly at cold temperatures, and will eventually cause spoilage. This is why you can only keep opened packages of meat and seafood in the refrigerator for a few days before they go bad.