Preservation Methods

I have done some research on the common types of preservation method used.


CANNING
Canning is the process in which foods are placed in jars or cans and heated to a temperature that destroys microorganisms and inactivates enzymes. This heating and later cooling forms a vacuum seal. The vacuum seal prevents other microorganisms from recontaminating the food within the jar or can. High-acid foods such as fruits and tomatoes can be processed or "canned" in boiling water, while low-acid vegetables and meats must be processed in a pressure canner at 115.6°C (10 pounds pressure at sea level).


FREEZING
Freezing reduces the temperature of the food so that microorganisms cannot grow, yet some may still live. Enzyme activity is slowed down but not stopped during freezing.

Enzymes in Vegetables: These must be inactivated by blanching in order to prevent loss of color, flavor and nutrients. The vegetable is exposed to boiling water or steam for a specified time and then quickly cooled in ice water to prevent cooking. Blanching also helps to destroy microorganisms on the surface of the vegetable.

Enzymes in Fruits: These can cause browning and loss of vitamin C, and are controlled by the addition of ascorbic acid.


DRYING
Drying removes most of the moisture from foods. Thus microorganisms cannot grow and enzyme action is slowed down. Dried foods should be stored in airtight containers to prevent moisture from rehydrating the products and allowing microbial growth.


Source: http://hgic.clemson.edu/factsheets/HGIC3000.htm