The primary methods of preserving food include:

• Retards growth of microorganisms.
• Slows action of enzymes.

Freezing

• Prevents growth of microorganisms, but does not necessarily kill them.
• Slows, but does not stop enzymatic activity. Therefore, enzymes in most fresh vegetables must be inactivated by blanching before freezing.
• For highest quality, lower the food temperature to 0°F as rapidly as possible and maintain a 0°F food temperature.
• Freeze only the amount you can use before its shelf life expires ( see Storing Foods at Home , EB1205).
• Use packaging that is moisture proof, sealable, and oxygen impermeable to retain quality

Canning

• With proper canning practices, air is forced from the jars, leaving a vacuum. Heat destroys the most heat-resistant microorganisms capable of growing in food stored at room temperature.
• Molds and some yeast are unable to grow in a vacuum. However, there is a very healthy growth environment for anaerobic bacteria in sealed, home-canned foods. Such foods must be heat processed until a commercially sterile product is achieved, or they must have salts, sugars, acids, or other preservatives added.
• Yeasts and molds are destroyed when food temperatures reach about 190°F, whereas most bacterial vegetative cells are destroyed in foods heated to a boiling temperature. Bacterial spores are able to survive for a long period at the temperature of boiling water.
• Pressure enables the processing of canned foods at temperatures higher than boiling water, where kill rates are greatly increased. Pressure canning is required to safely process foods that may support the growth of bacterial spores.

Sweetening and Acidifying Jellies and Jams

• Adds sugar and acids that tie up free water and lower pH.

Pickling and Fermenting

• These methods (and others, like canning naturally acidic fruits, jams and jellies) use either naturally produced or added acids to inhibit or prevent the growth of many microorganisms. Foods that contain enough acid to inhibit the growth of Clostridium botulinum are called high acid foods (pH lower than 4.6). The presence of acids in foods, however, does not kill organisms.
• Fermenting uses bacteria to produce lactic acid and lower the pH in products such as fermented pickles and sauerkraut.
• Pickling adds vinegar (acetic acid) to lower pH in fresh pack pickles and other acidified products.

Drying

• Removes water and prevents growth of microorganisms.
• Water in fresh food exists in free and chemically bound forms. Microorganisms require free water for growth. Removal or reduction of free water from a food prevents growth of microorganisms and controls enzyme activity.
• Dried foods must be packaged in oxygen and moisture proof containers to prevent oxidation of flavors and moisture gain.

Salting

• Chemically bonds water, inhibiting growth of some bacteria.

Packaging - The success of all preservation methods depends on using appropriate packages . Airtight packages prevent recontamination of foods by air and microorganisms and are ideally suited for most preserved foods.