Just as microbes need water, most also need air. Reducing the air supply almost always reduces the bacterial population. The exception is anaerobes (microorganisms that can live without air), such as botulinum organisms, which thrive in the absence of air. Go figure!
Foods are protected from air by vacuum-packaging. A vacuum — from vacuus, the Latin word for "empty" — is a space with virtually no air. Vacuum-packaging is done on a container (generally a plastic bag or a glass jar) from which the air is removed before it's sealed. When you open a vacuum-packed container, you hear a sudden little pop as the vacuum is broken.
jfe. If there's no popping sound, the seal has already been broken, allowing air inside, and that means the food inside may be spoiled or may have been tampered with. Do not taste-test: Throw out the entire package, food and all.
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