“If the can is not puffy it is safe to eat”
Had a can of tomatoes explode in my pantry once. What a mess.
Expiration dates on tomato base can goods is the only one I take seriously.
That would be the case for any acidic food.
The acid can eat away at the can lining and then the can. It’s called detinning and the metallic taste is terrible. I actually encountered some maple syrup that did that. Now when we buy maple syrup, we get a gallon (best price option) and I heat it up to boiling and then can it into pint canning jars and seal it with hot lids then just let it cool. I don’t even process is as the sugar content of the syrup means the temperature is plenty hot enough.
The maple syrup keep indefinitely that way and has never crystalized on me.
Home canning in glass canning jars takes care of that problem.
Yes (its the PH), and heat any old food well.