I was taught to always bring any soup or stew to a rolling boil for at least two minutes, especially homemade soup (from the fridge, or canned). but my grandparents and parents always did the same with store bought canned soup.
That’s why I refuse to heat soup in a microwave. I want it in a pot boiling for at least two to three minutes to kill any pathogens.
I remember my grandmother kept a soup starter in the fridge. She took it out every day and boiled it for five minutes. She added more water, vegetables and stock whenever she served soup. It was great soup, and much better than store bought. No one ever got sick from that Soup starter.
She had to throw out her soup starter when they left the house to visit family. She insisted it had to be brought to a boil every day.
Well, then don’t use dented or swollen cans. But why would that mean you couldn’t trust perfectly good cans? What if you opened a can of tuna or pet food? How would you sterilize that? Tuna boiled for two minutes doesn’t sound too good.
Where does it end? What would you say to a woman who soaked her store-bought apples in rubbing alcohol, because there could be germs and her grandpa always did that?
I think it’s a combination of paranoia and the very powerful psychological pull of “This is how I was taught.”
My wife and I had to do a lot of adjusting, because we’d both had mothers who were SURE there was a reason for their quirky kitchen rules. Finally one day my wife admitted her only logical reason was “My mom always did it this way!” When I asked why SHE had to do it that way, she said “But my mom’d be mad if I did it that way!”
(I thought but didn’t say “Yo’ mama is 3000 miles away and in her 90s, she ain’t droppin’ in…”)
I bring them to a boil but it’s because I like hot things really, really hot. If I bring it to a boil I know it’s hot enough. I don’t think it’s necessary for food safety though.
I have never gotten sick either from the hundreds of canned food items I’ve eaten without boiling them first. In fact, I can’t recall in the national media anyone getting food poisoning from store-bought canned food, and honestly, I don’t think I’ve ever known anyone who cans their own food. I would probably boil home-canned food, if I ever had cause to eat it, but that will probably never happen.
I tend to microwave canned soup. However, I’ve eaten it cold before now, poured out of the can straight into a bowl, with no thought that this would be an issue.
Soup stock is slightly different, though, although daily boiling is probably over kill.
I also make beef stew in a slow cooker, that sits all day at about 90C and never gets to a rolling boil.
When people talk about bulging cans, they are usually talking about botulism, and if your canned food is infected with botulism, boiling for a couple of minutes isn’t going to do any good.
Fortunately, botulism in commercially prepared canned food is not a significant concern these days.
I usually do, but not because I think it’s necessary, just because boiling is a very noticeable sign of being heated. If for some reason I happened to notice it before it was boiling, and it was at an acceptable temperature, I’d take it off and serve it then.
As long as your grandmother was keeping her soup starter in the fridge when it wasn’t on the stove, it should stay fine for a good while.
Wait, when you say home canning, are you saying you had family who canned homemade soup (presumably in mason jars)? I’ve only ever heard of home canning being used for things like pickles, preserves and the like. Never for stuff like soups.
And you mentioned your distrust of canned foods stemming from childhood. That seems a bit odd to me, as canned foods, including Campbell’s condensed soups, have been available in the US for over a hundred years. Was your family just distrustful of new ideas?
Edited to add that I think that bringing something like a canned chicken noodle soup to a roiling boil for a couple of minutes is going to start to break down the noodles and some of the other stuff.
I actively try to avoid rolling boils in soups and stews and would consider it poor cooking practices. I like my soups/stews hot but don’t want to burn stuff to the bottom of the pot. So get it to a start of a boil, then stir once, and let it return to a starter boil is usually how I would do it. Also if slow cooking for a while the soup becomes pasteurized, at about 180F IIRC for some time.
I used this method for a while, single pot cooking, usually a pressure cooker, same stock every day. Food came out better and better each time (usually chicken), but if the water level dropped too low and it started to burn then it was time to start over. It was never a issue in the context that the OP is talking about.