Actually, Grace, your information is partially out of date.
Back in the '80s there were five true low-acid tomatoes introduced. Because of those, USDA revised its recommendations (in 1988, actually), suggesting the addition of lemon juice to make up for the possibility that low acid tomatoes would be used by home canners.
Four of the five varieties were almost immediately taken off the market, because nobody liked them. The fifth, until last year, was only available to commercial canners who wanted to put up a low-acid product (comercial processes are not the same as home canning, and the same rules don't apply).
Last year that final low-acid tomato was taken off the market. And, as I said, it wasn't available to home canners anyway.
But, like most gubmint regulatory agences, USDA locks itself into rules. Once standards are established they only get changed to make them more restrictive, never less.
I would suggest that even hybrids (ugh!), if tested with a pH meter, would come in more than acid enough for safe canning.
That aside, most salsa recipes I've seen designed for canning specifiy pressure canning, because there's enough onion, peppers, and other non-acid ingredients to seriously impact the pH.
The problem is that it's difficult to process chopped tomatoes at 10# for any length of time without them cooking down. So it's hard to get a chunky canned salsa.  |