Eli5: how does canned food last so long while the can is sealed? Does it use preservatives?
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Canned foods have had all the bacteria that could spoil it killed during the canning process. The process uses heat which is why there’s not raw ingredients from cans.
The heat kills the bacteria and also denatures enzymes that cause the food to break down.
Additionally when something is heated it expands. Canned things are canned hot so when it cools there is a relative vacuum. So there’s very little air for bacteria, and they were killed during the heating process.
This is then sealed in a closed environment, like a can, and that’s how it’s kept stable.
Edit:
To add to the preservative question- Sometimes.
Home canned things don’t need them, but companies can put things in there to make the food look better, have better texture, or flavor since the food is essentially being cooked to hell the first time. There needs to be a certain pH range and salinity to stop botulism but if the food falls within the safe parameters it’s k.
Some foods have preservatives like SPAM but that’s sodium nitrate which is also in cured meats like bacon or ham.
If done properly, the food is sealed in an environment with little or no oxygen and no bacteria. There’s basically nothing in there with the food to spoil it (unless the food is somehow self-spoiling), so it stays relatively fresh.
Which is also why a ‘bloated’ can should not be used – the extra gas produced while the can was sealed means that the canning *wasn’t* done properly, bacteria survived and have been merrily eating and reproducing since.
I think tinned food works where there is very little oxygen in there for any mould or bacteria to thrive
Generally no preservative is needed. The concept of canning is to not have to use preservatives though. By making the food completely sterile and then sealing it in an airtight can there are no bacteria or air which can cause the food to go bad. So a can of food can stay good even after years of storage.
However there is quite a bit of difference between various types of food. Some can go bad without bacteria or air by the chemicals in the food themselves degrading over time. It may just be a change in taste or texture and still be perfectly fine to eat but this is something you want to avoid anyway. So it is not uncommon to use some type of preservatives in canned goods. But a lot less then in other type of food. And a lot of these preservatives is things you not always think of as preservatives. For example brine, canola oil, table salt, vitamin-c, vinegar, etc. Things like you might add to the food anyway.
Boiling vegetables and pickling foods preserves it salt is used or sugar as a preservative along with citric acid to improve color. Canned foods are boiled and seal to reduce bacteria and molds and prevent them from growing. The air pressure may diminish after cooling making a slight vacuum in jars.
Cans have three advantages that help preserve food:
1. Cans block out light. Light, especially UV light, can cause chemicals in food to break down.
2. Cans are sealed against oxygen. Oxygen is a major cause of foods spoiling, so protecting the food from oxygen improves the life. The better the seal, the longer the food will last. Plastic wrap or bags protect against oxygen a bit, but glass or metal containers are much more air tight. Once the can is opened and oxygen gets in, the food can spoil fairly quickly.
3. Foods that are canned are usually sterilized, killing any bacterial in the food that could break it down or rot it. Until you open the can for the first time, there will be no bacterial action.
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