I thought of that, but while that might be the correct source, it doesn't make much sense given current knowledge/practices.I've never seen it written any where. Wondering is it something that was passed along from back when lots of folks water bathed everything?
That's all I could think of?
Currently, all soup canning recipes use pressure canning to eliminate the possibility of botulism. That eliminates the need for any boiling after opening for safety. You only need to bring the soup up to temperature for eating.
If you use water bath canning, then most pathogens are eliminated and the *only* benefit of 10 minutes boiling is to kill them off if you did a poor job of canning. Botulism (and the toxin it creates) can survive both water bath canning and 10 minutes boiling, so the additional boiling doesn't eliminate this potential problem.
I'd like to know if anyone can find a documented reason for the additional boiling. At this point, I don't believe it.