DIY





Vacuum Packing and Nitrogen Packing Foods

Learn how to safely remove oxygen from food storage containers.

| August/September 1999

Free oxygen is a major culprit in food spoilage. When food browns, its components join with oxygen, or "oxidize," much as iron does when it rusts. Oxygen is also necessary for molds, yeast and aerobic bacteria to survive and wreak their damage. You needn't worry with canned foods that have been properly heat/vacuum-packed. But lacking such in-container heat-treatment, even if a sterile product is vacuum-packed in sterile containers, the small amount of air that accompanies it will contain oxygen and may not have been heated sufficiently to kill spores that have been faithfully killed on container and in product.

You can purchase vacuum-baggers in many catalogs, off the Internet and from TV advertorials. They cost $100 or more. The one I have uses a handheld pump to evacuate air from both plastic freezer bags and special vacuum canisters. Others suck out the air, then heat-seal the bag.

These things are best for fresh or freshly opened foods that you want to keep fresh in a refrigerator or for dry foods such as chips that you want to stay crisp. Lettuce will keep for weeks in an evacuated bag, cheese for months, Tostitos for all eternity.

The most effective way to prevent oxygen damage is to remove and replace the oxygen with an inert gas. All those clear cello-packs of potato or corn chips, pretzels or popcorn that display their contents of salt and greasy calories so effectively on supermarket shelves are inflated with nitrogen gas. Punch a small hole in one and squeeze the gas inside onto a burning match. The flame will go out.



To store grain and dry goods for years, keep them in plastic bags filled with nitrogen and sealed inside plastic tubs or metal cans.

You can have food-quality nitrogen delivered and empty containers picked up by medical gas suppliers. It comes in pressure bottles similar to propane tanks (don't try liquid nitrogen). The long bottles must be supported upright in a rack or wheeled daily, and you'll need to rent or buy a nitrogen pressure regulator to keep the gas at low pressure.






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