Is it mostly a matter of just depriving the contents of oxygen? Why does that work?
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What destroys food is mainly microbes like bacteria
The goal of food preservation is to make that food as unpalatable to bacteria as possible.
Storing cooked food in vinegar (pickling) for example makes an environment that microbes can’t survive in.
Sealed cans prevent bacteria from getting in, and the food inside is cooked and pasteurized to kill off any microbes inside.
Flour, rice, pasta, etc uses another technique which is drying. The water content of that food is so low that microbes can’t survive.
It is a way to store the food in a sterilized container. Depending on the food you can add a preservative (salt, acid, even sugar in high concentrations). The food itself is often heated to sterilize, and the jars themselves are sterilized by heating as well. Sometimes this is done at the same time: the filled jar is heated.
This kills the micro organisms that want to eat the food and make it „go bad“ for us. Since the container is airtight, no new micro organisms can get in. There is also very little oxygen in the jars. In industrial packaging, they often replace the air with pure nitrogen for the same reason.
You usually seal the can and then boil the sealed cans. That kills all the bacteria that happened to be inside with the food. Once it cools, you now have a sterile can with no bacteria inside, and its sealed so no oxygen can get in either. With no bacteria AND no oxygen, pretty much all the food spoiling reactions can’t happen, so it’s stable for a very long time (theoretically until the seal on the can fails).
Its about taking some food that can be a source of nutrition for you in the right conditions. Yet making it not useful to other organisms. Think of fencing off a chicken coop. You keep out the foxes. Fencing a garden will keep deer out, etc. In this case, we are canning food and “fencing” out bacteria. But they are soo small that you cant fence them out entirely, so we do stuff that kills it as well. That is going to be heat/acid/salt which will keep bad stuff out.
Pickling is a bit different, you do all of that. Heat, salt, etc. But why do pickles taste like pickles? A certain type of bacteria is left after heat and salt. So, part of the taste of pickles comes from certain bacteria waste which isnt bad for us. Life is crazy.
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