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Vacuum packing is the process of packaging items, particularly perishables like meats and other foods within an envelope of impermeable plastic while removing as much of the air from the inside of the package as possible. The removal of the air from inside the food reduces oxidation of the food and helps to prevent spoilage. Foods that are vacuum packaged remain fresher for considerably longer than foods packaged by other means. Vacuum packing is also used to reduce the bulk of non-food items for increased storage efficiency.
The meat industry in particular makes extensive use of vacuum packing. This technology has made it possible for meats to be packaged and kept fresh for a period of time that exceeds that allowed by other methods, making it possible to ship meats over longer distances and to bring meats to markets that would otherwise be unreachable. Other types of foods are kept fresh by this method as well, such as coffee, seafood, and many dried foods. Machines for home use allow individuals to vacuum package their own foods.
Machines envelop and seal the food in plastic while removing the air from the package. The removal of air from the package prevents oxidation, which is the reaction of oxygen with the food. Oxidation is a key component in the process of spoilage. Foods that do not decay and go rancid but simply become stale can also benefit from vacuum packaging, as the absence of air prevents the foods from absorbing moisture.
Bacterial growth is reduced by vacuum packaging as well. Since foods are packaged under controlled, sanitary conditions, bacteria are kept away from the food, preventing many harmful bacteria from breaking down the food. The action of bacteria on foods is another primary component of food spoilage. Yeasts and molds, which require oxygen, also have reduced growth in vacuum packaged foods.
Vacuum packing of frozen foods also helps reduce the incidence of freezer burn. Freezer burn can occur as moisture is drawn from the food and the food becomes oxidized and dehydrated. Vacuum packed frozen foods resist freezer burn due to the absence of air in the package.
Foods that require refrigeration under normal conditions will still require it even if vacuum packed. Vacuum packing slows food spoilage by removing air and eliminating available oxygen, but there are harmful organisms that do not require oxygen and that continue to act on food. The action of these organisms is slowed under refrigeration. Vacuum packing is not a substitute for refrigeration, but merely an aid to prolong the shelf life of foods.
Machines for home use also allow individuals to vacuum package their own foods. Vacuum packing, however, in no way preserves or sterilizes food on its own, but merely preserves the condition of foods when they are packaged. This means that vacuum packing is not a substitute for heat sterilization of foods canned at home.
You can use a vacuum packing for almost everything and I find it a great tool. It doesn't matter that it hasn't been changed for a long time; it's still great!