That’s interesting, I’d never heard of anyone doing that. I’ve canned butter before. One persons website I read says they’ve been doing it for years and sometimes the butter would be several years old before they used it. Then freaked out when I read about a dangerous bacteria you can get from canned butter, or lard. I can’t remember what the bacteria was called but, it wasn’t a good thing. It’s something that hides in fat and is very hard to kill. Can survive without oxygen, and I don’t think it was salmonella, botulism or listeria.
It used to be that hogs were really fat and the bacteria came from not cooking the pork completely. Todays hogs are raised with low fat and lots of muscle. I have a friend who breeds and raises them.