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
The factory that produced it did so in some kind of clean room with a flow hood to reduce the amount of spores that can contaminate it. Its kinda like canning but by making the food clean before adding it instead of doing it in the can
Because before you opened it, the jar’s contents was in a sterile, oxygen-free environment. Once you open that jar, air containing things like microorganisms, mold spores, dust– knives carrying dirt and saliva from whoever licked the knife and then re-used it– the container starts collecting things– so you have to keep it refrigerated to slow / stop the growth of microorganisms and fungi from spoiling your mayo.
Two reasons.
When they produce, for example, mayo, they sterilize it. In the jar, there will be almost no bacteria.
Then, they seal it in a controlled atmosphere (low oxygen) to make life difficult for bacteria and mold
Fun fact, Mayo doesn’t need to be refrigerated after opening either. However, better with the squeeze bottles or using a fresh scoping utensil and not touching bread/food and then going back for more. The contamination comes from stuff going back into the jar. Obviously don’t keep past use by date.
How do I know this? A restaurant I used to go to had Hellmans/Best Food Mayo containers on the tables that said “no refrigeration required”. I asked them to buy some because we frequently go camping and fridge space is limited. Restaurant closed down so I called Hellmans/Best and asked about buying that Mayo without being a business. They told me the consumer and commercial are the same, no refrigeration required as long as not cross contaminated and used before the date. The reason they put that label on the restaurant bottles is so people don’t freak out seeing the Mayo left out!
Now for almost any other product, what everyone else said is correct.
As others have said, pasteurization has been a thing for a long time. We also have gamma ray sterilization used in some instances which is more effective for particular cases (no pathogen can survive its DNA being obliterated), but it also can break down the cells which are part of the food (most everything if not everything we eat is derived from nature to some degree so it still has cells)
That all goes out of the window when it’s opened and the open air brings in new bacteria though
As someone who used to work for Hellmann’s, I assure you that mayonnaise is not pasteurized. If it got heat treated after packaging, it would be thoroughly cooked and the emulsion would break.
Mayonnaise is formulated to stop bacteria and molds/yeasts from growing in the product. I did a ton of experimentation on this subject. Strangely, the original post that said this got down voted to oblivion.
The small amount of water in mayonnaise is dispersed and acidified. Mayonnaise literally kills germs. Once it’s been opened, there’s a risk that you’ll contaminate it with stuff that’ll allow nasty germs to grow. Rather than take on that risk themselves they pass it to you.
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foods go bad from microbes, enzymes and oxyge. packaged stuff have long shelf lives because these factors have been eliminated during the manufacturing process and the packaging is good at keeping external sources of these out. once you open the box, you reintroduce them from the air, your spoon, saliva, etc and it starts to spoil again, albeit not as fast as the fresh stuff because it starts at zero and probably still has active preservatives.
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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