[thecodont]

But recent years even red tomatoes have been bred specifically to be low acid.

Looking through seed catalogues, I have come across varieties that are mentioned as being "old fashioned" canning types, higher in acid: varieties such as Old Brooks and Bonnie Best.

[handmade]

There are some seed catalogs that contain a wealth of information. I received two catalogs this year that were half an inch thick and full of information.