Had a conversation with my wife today about the unopened mayo we had sitting in the pantry and it made me think – how does it make sense for a food (for instance mayo) to sit in a 65-70 degree pantry for months and be perfectly fine, but as soon as it’s opened it needs to be refrigerated. In my mind, if something needs to be refrigerated at any point, wouldn’t it always need to be refrigerated? The seal on the unopened product keeps the item safe, and the refrigerator does that when the seal is off? How do those two things relate?
In: 1789
Before opening, the food is sterilized. There are many methods of accomplishing this, including, but not limited to: pasteurization, irradiation, altering the chemical makeup, heating, boiling, and pickling. The chosen method often, but not always, determines whether the food needs to be refrigerated after opening, and the shelf life both before opening and after. For example: peanut butter in a jar at the local grocery is chemically altered to prevent bacterial growth (particular formula and using nitrogen for the headspace) and is shelf stable for a year or two before opening and several weeks after. However, peanut butter in emergency rations is chemically altered (particular formula), vacuum sealed (no headspace of any kind), AND irradiated, giving it a pre-open shelf life of 10+ years and a post-open shelf life of…who knows?, you’re opening a single serve pouch at a time.
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