Tomatoes top the list of popular garden produce and commonly canned foods. But, some people still have not heard that when canning tomatoes of any variety, adding an acid is a vital, non-optional safety step, even though this safety protocol has been recommended for nearly 30 years.
Properly acidified tomatoes can be safely processed in a boiling water bath or pressure canner. Add the acid to the jar before filling with tomatoes. Use 1/4 teaspoon commercial citric acid powder, or 1 tablespoon bottled lemon juice or 2 tablespoons vinegar per pint. Citric acid gives the best results with no added flavor of its own. Lemon juice and vinegar create competing flavors, which some find objectionable. But all three options produce safe canned tomatoes. See more at www.bookstore.ksre.ksu.edu/pubs/MF1185.pdf.