Healthy Canning has this to say about their credentials : We are not scientific researchers or credentialled canning experts source. As I said, that was a quick search. I’ve read the recommendation on several extension sites. Extensions are a generally trusted source of info, so OP’s question is legit. I explained the thinking behind the recommendations that OP had heard. I also noted that I often don’t feel it’s necessary but I felt an explanation was still warranted. You’re free to ignore them, but dismissing rather than discussing does nothing to help OP’s understanding.