All researched-based recipes for canning tomatoes and salsa require the addition of an acid, such as lemon juice, for safety. I am often asked if this step is really necessary and why. My answer to this is an enthusiastic “Yes!” and I hope that the following information will help to explain why (and how) to do this properly.
Acidity
The acidity or alkalinity of a food, known as pH, is a critical factor in determining how to handle that food safely. If the pH of a food product is lower than 4.6 (such as most fruits), it is safe for a water-bath canning process. Food products with a pH higher than 4.6 can support the growth of Clostridium botulinum, which creates the toxin that causes botulism poisoning. Though this poisoning is rare, the botulism toxin is one of the most potent toxins known.
Tomatoes Vary in Acidity
Research has demonstrated the acidity of tomatoes to be between 3.7 and 5.2. Acidity can be affected by variety as well as growing conditions, the stage of ripeness, and the presence of decay or damage. In fact, tomato decay or dead vines may reduce acidity enough to make the tomatoes unsafe for home canning!
Add-Ins
Salsa is mostly tomatoes, of course, but also includes a variety of additional ingredients—some more acidic than others. Since many tomatoes may not be acidic enough to inhibit the growth of Clostridium botulinum, it is recommended that we add a specific acidic ingredient to ensure our tomato products (including salsa) are safe for water-bath canning. The following table illustrates three options for acidic additions and the recommended amounts:
*Note: you may choose one of these acidic additions, you do NOT need to add all three!
Your acidic ingredient may be added to each jar prior to filling. If using lemon juice, be sure to use commercially bottled lemon juice, as the pH of freshly squeezed lemon juice may vary. A small amount of sugar (1-2 teaspoons) may be added to offset the taste of the acid if desired.
Follow Research-Based Recipes
When canning your tomatoes or salsa, it is important to follow a research-based recipe to ensure safety. Recipes from University Extension publications are great, of course, and Ball® resources can be trusted as well. Many other resources, such as books, magazines, and internet sites may have recipes that are not researched for safety!
Food Preservation Sources Approved by the University of Wyoming Extension:
- “Preserving Food in Wyoming,” UW Extension (2024): https://bit.ly/wyo-1210
- USDA Complete Guide to Home Canning, revised 2015: https://bit.ly/usda-canning
- Ball Blue Book Guide to Preserving, 38th edition (2024)
- New and Updated Ball Complete Book of Home Preserving (2020 edition)
- Ball Canning Back to Basics (2017)
- The All-New Ball Book of Canning and Preserving (2016)
- So Easy to Preserve, 6th edition (2020)
- Commercial pectin recipes and manufacturer’s instructions, and
- Other up-to-date extension publications