Why do food items that say “refrigerate after opening” not have to be refrigerated before opening?
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There are many processes that can more or less kill or limit micro-organisms within the sealed container, but opening it can introduce new micro-organisms from the air, and crucially, also introduce oxygen many require to grow.
Short Answer:
Because lack of oxygen can also work as a way to preserve food, but stops working the first time you break that seal.
Long Answer:
You can protect the food from the microscopic organisms that would cause decay one of three ways:
1 – Keep those organisms out by having an airtight seal.
2 – Keep those organisms from growing by denying them oxygen.
3 – Keep it too cold for most organisms to function. (Cold enough that they either die or if they are alive their metabolism is very slow.)
At the factory, they can do #1 and #2 really really well. They can have a very sterilized environment when they seal the jar, bag, or whatever, so it didn’t have many organisms inside the package in the first place. They also sometimes seal them in a way that the air trapped inside is almost pure nitrogen: air that has had the oxygen removed. (This is the case in potato chip bags. That air that makes the bag puffy – that’s nitrogen-only air, not the normal mix of gasses you normally find in the atmosphere.)
Techniques #1 and #2 are sufficient on their own when done well.
But once you break that seal, you let in “normal” air that has oxygen in it and has some microbes. You can re-seal the package as tight as you want but it still got some of that stuff inside before you sealed it. At this point you have to add technique #3 because you weakened the effectiveness of techniques #1 and #2.
They’re sterilized when they’re sealed. We refrigerate things to slow down bacterial growth. Until the sealed container is opened there’s no bacteria inside to grow so the things we do to slow down that growth aren’t necessary.
Some items like Ketchup and Mustard will say that to prevent pathogen growth, however they are not high risk. There is also a chance it’s the manufacturer’s recommendation so you enjoy their product to the maximum. Then you dont write nasty letters complaining about the product.
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Because they degrade faster when warm. Even if they don’t grow bacteria to dangerous levels they won’t taste as nice as long. Also probably because the manufacturer is covering their ass.
The process of sealing/filling the bottle, jar, or other container sterilizes the interior. So any harmful bacteria or growths aren’t present.
When you open it. You unsealed it and now those critters got in. So the only way to keep it from spoiling faster is to keep it refrigerated to restrict their growth.
Question: If an item is still sealed (say a coke bottle, or a pack of juice) and I put it in the fridge, but a few days later I take it back out because I need the space, is that okay?
Yo go from non refrigeratted -> refrigerated -> non refrigerated again? Sealed the whole time.
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