Food preservation technology has made great strides in recent years. However, not every new technology is safe.
"Modern devices such as vacuum sealers, if they are used incorrectly, also may be dangerous," said Gail Slinde, Ward County Extension Service food specialist -- "in part because the signs the food is spoiled are not as visible."
Equipment for vacuum packaging food at home, usually called vacuum sealers or vacuum packing machines, vary in price and technological sophistication, depending on the brand. But they are not a safe substitute for heat processing of home-canned foods, she warned.
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Cleo Cantlon/MDN - - Gail Slinde holds a vacuum packing machine and plastic bags for freezing and storing food.
Vacuum sealers also do not substitute for storage in the refrigerator or freezer for foods that require it. In fact, such handling of foods not stable at room temperature can actually add to the danger because people packing those foods at home assume it is safe
"The same precautions you use for those foods when you did not vacuum seal them must be followed in thawing," Slinde added.
Producing a vacuum or partial vacuum with one of these machines means removing air from the package. That does help reduce some of the deterioration of foods, such as color change promoted because of oxygen present in the packaging. Ground meat turning dark in storage is an example. It can extend the food's shelf quality.
However, removing oxygen affects but doesn't eliminate all bacterial growth.
"In fact, what vacuum packing eliminates is growth of spoilage bacteria that ordinarily causes odor, color changes or a slimy feeling," Slinde said. "But those changes, unwelcome as they are, warn cooks that food is going bad before it is served and gives a chance to cause illness in those eating it. In that vacuum-packed, oxygen-free environment, spoilage bacteria don't multiply very fast."
Some illness-causing bacteria love low-oxygen environments where they reproduce very well, sometimes even more rapidly because they have no competition from spoilage bacteria. The changes they make are not as noticeable. Food may become unsafe without visible warning.
The dangerous pathogen that causes botulism, for instance, grows at room temperature in low-acid moist foods in those low-oxygen conditions. Refrigeration at 38 to 40 F is critical to keep those foods stable.
"When is a vacuum-sealing machine a wise investment?" Slinde asked. "Individuals need to consider the financial cost and the amount of use the machine would get in their kitchens."
Removing or reducing oxygen by vacuum packing is helpful in extending storage quality for non-perishable dry foods like nuts or crackers because their low moisture prevents that bacterial growth, Slinde said. Vacuum packing is also an asset for food that will be stored frozen. However remembering to thaw in proper conditions is essential.
Perishable food being vacuum-packed shouldn't be out of refrigeration, above 40 F, for long -- no more than two hours total time.
Clean hands, clean and sanitized equipment and work surfaces are essential. Food should be dated and used within reasonable storage times unless frozen, and raw meats, poultry and seafood must be cooked thoroughly to recommended temperatures, measured with a food thermometer, before eating.