Eli5: why do certain refrigerated products require us to consume all once opened? Why can’t we eat some and refrigerate it again to consumer it later?
In: 24
Because normal refrigeration can’t stop bacteria growing and spoiling the food, it merely slows it down.
Some food are particularly prone to spoiling so they are sealed and superheated to completely kill all bacteria inside the package. Opening it exposes it to bacteria again and it will spoil quickly even if you put it in the refrigerator.
Most products spoil in regular air due to oxygen, however to combat this in certain products (i.e. jam, a bag of chips, drinks) that clearly have air in them will sometimes be filled with nitrogen. Nitrogen is nontoxic, nonflammable, and will help preserve food since mold and bacteria can’t strive without oxygen. As soon as you open something, you are introducing oxygen.
Side note, some products will last a lot longer in normal temp even with oxygen due to many factors. Either PH levels are toxic to bacteria (hot sauce and vinegar) or there is simply not enough water for anything to live in (honey).
Edit: As to why we refrigerate after? It’s simply to slow down bacteria and mold. But unless you freeze it, it won’t stop the bacteria and mold completely.
Can you please make an example (or several please) of such products? (This will be ELI5 or maybe TIL for me). I cannot think of any product on my fridge (or at the store) that needs to be consumed all at once.
Temperature is the most important factor in bacterial growth. In the fridge it is slowed down, but not stopped. Also bacterial growth is exponential.
In the correct circumstance, under room temperature, highly perishable food (fruit, milk products, raw meat) can reach critical bacterial growth (aka spoil) in a few hours.
Even if the bacterial numbers are not critical when you put it back, due to the exponential growth, it could be enough to reach critical numbers very quickly, even with the slowed growth in the fridge.
That being said, it mostly depends on how long it is exposed to ambient temperatures. If you take a jar of yoghurt out of the fridge, scoop some out with a clean spoon and put the rest back immediately, it will still be edible for days.
If you eat directly out of the jar (introducing more bacteria) and leave the rest on the counter for half an hour where it gets to warm up to room temperature, outcome might be vastly different.
Apart from the scientific reasons earlier addressed, there is also liability. If you get sick from something but yu haven’t taken the (sometimes ludicrous) mentioned precautions, you will most likely not make a formal complaint
I’ve only seen packaging say “after opening, keep for limited time” but that generally means more than a week
The longer it’s opened, the less safe it becomes as it’s now exposed to oxygen and bacteria. Chances are bacteria from your mouth also got into the food.
In the short term this isn’t a bit deal, but the issue arises when people put food back into a fridge and let it sit for days/weeks, then eat it again and get sick. They then go on to complain about how that food was “unsafe” to eat.
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