Salsas are usually mixtures of high acid foods, such as tomatoes and/or fruit, with low acid foods, such as onions and peppers. With the addition of lemon juice, citric acid, or vinegar in the right proportion, salsa becomes a high acid food and can be safely processed in a boiling water canner. However, only research-based recipes should be used. Other salsa recipes, found on the internet, in published books, or from grandma’s recipe stash, should not be home canned unless they have been properly tested for safety. Enjoy those salsas fresh, or frozen for longer storage.
The recipes included in this publication are research-based for safe home canning. Do not change the proportions of ingredients. However, one variety of pepper can be substituted for another in the same amount (for example, bell peppers for hot peppers to make a milder salsa). Likewise, red, yellow, or white onions may be used, as long as the total amount of onions in the recipe is not increased. Green tomatoes may be used in place of ripe tomatoes, but the flavor will be different. The amount of lemon juice, lime juice, or vinegar should never be changed. To ensure a safe level of acidity in the final product, use only bottled lemon or lime juice and commercial vinegar that is at least 5 percent acidity. Sugar may be added to taste if desired, and spices and herbs can be varied.
Bastin, Sandra and Clouthier, Debbie, "Home Canning Salsa" (2015). Family and Consumer Sciences Publications. 109.