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
It’s because once you open the mayo, you expose it to air and bacteria, which can cause it to spoil
Refrigeration slows down the growth of bacteria and helps keep the mayo safe to eat.
As long as the jar is sealed, it has been sealed with no bacterias in it. Bacterias are the whole and only reason why food spoils. The moment you open it, bacterias from the air start filling in and feasting on the stuff.
Way back in the late 1800’s there was a guy named Louis Pasteur. He theorized that foods spoiled by the action of tiny organisms called “bacteria”, and that food could be prevented from spoiling if it were sealed inside a container that would prevent bacteria entering and then all the bacteria inside killed off (usually with heat). The sterile inside of the container then would not have any bacteria to spoil food and it could be preserved for long periods of time, a processed that came to be known as “Pasteurization”. His theories and experiments disproved the previous concept of “Spontaneous generation” where such organisms were supposed to just spring out of materials for no reason, like maggots appearing in rotting foods essentially via magic.
The mayo in your pantry has been sterilized after it was placed inside its container and so there is no bacteria to make it spoil. However the instant you open it the container will be contaminated and you will need to refrigerate it to slow their growth.
A properly sealed container of something that can go off like mayo is sterile inside, so it can sit on a shelf for a long time, first at the warehouse where it was made, then on trucks to the grocery stores, then on the grocery store shelf to your pantry.
The minute you open the container, germs from the air get inside and the food will spoil unless you refrigerate it, which slows down but does not eliminate growth of bacteria or mold.
Your mayo would go off quickly in your pantry if it was not sealed properly.
Pasturization is when a sealed item is boiled/heated to kill any bacteria in it, effectively rendering it “sterile”, but when you break the seal, bacteria in the air can now enter the product and contaminate it.
Refrigeration slows down the growth of bacteria, but does not prevent it entirely.
In addition, some foods may degrade/separate from heat over time, which is why they also benefit from being kept refrigerated.
When it’s in a sealed jar, it’s been sterilized to kill any bacteria inside the jar, can, etc. It’s a vaccuum where no air can get in. Once it’s opened and exposed to air with bacteria floating around, it has a limited lifespan before it will eventually spoil. But the cold air of a fridge does dramatically slow that process.
Bacteria cause spoiling, and they work faster at room temperature than they do in cold temperatures. They are present in ambient air. So, the sealed jar keeps them out almost entirely; the mayo can stay in a sealed jar for a long time. Once the jar is opened, game on, but the refrigeration helps slow down the bacteria’s game so that spoiling takes longer.
Thank you for all of the replies, the whole idea makes so much more sense now that I know about the sterilization process! What confused me was the sealing process, I assumed that bacteria was already in the product, when in actuality (taking from comments) the bacteria is killed off, ‘sterilizing’ the product and keeping it safe until the seal is removed!
A long time ago, people thought that mold and rot arose spontaneously within old organic material. Louis Pasteur was a French scientist who proved that if you kill microorganisms and seal a container they won’t grow inside the container. We named the process after him, and an enormous amount of food is Pasteurized for storage.
However, once you break the seal on the container microorganisms and spores in the air begin colonizing the food and it will spoil quickly unless refrigerated.
Most people nailed pasteurization as the main thing that *generally* applies to foods that are “refrigerate after opening” and “button pops up when seal is broken”.
Mayonnaise specifically resists growing bacteria, but contamination, such as with a knife that might have had other things on it, can introduce *other* food for the bacteria to munch on, and mixing mayonnaise with other food can make the mayonnaise more edible for bacteria.
And as with many foods, letting it sit warm (such as out in the sun) *greatly speeds up* how much bacteria can reproduce, so that even foods like mayonnaise that resist bacteria could still end up hosting a lot of it with enough time. The reason refrigeration helps is that it keeps the temperature low enough that bacteria grow slowly, even if it’s contaminated.
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