All researched-based recipes for canning tomatoes and salsa require the addition of an acid, such as lemon juice or vinegar, 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 boiling water 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—5.2. Acidity can be affected by variety as well as growing conditions, stage of ripeness, and 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 primarily tomatoes, of course, but it 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 in a specific acidic ingredient to ensure our tomato products (including salsa) are safe for boiling water canning. The following table illustrates three options for acidic additions and the recommended amounts:
| Acid ingredient* |
Add per pint |
Add per quart |
| Lemon juice |
1 Tablespoon |
2 Tablespoons |
| Vinegar – 5% acidity |
2 Tablespoons |
4 Tablespoons |
| Citric Acid |
1/4 teaspoon |
1/2 teaspoon |
*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 before filling. If using lemon juice, be sure to use commercially processed 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.
Salsa Safety
Only use scientifically tested recipes for canning! If you have a special salsa recipe, it is best to prepare and eat it fresh. If you want to preserve an original salsa recipe for later, freezing is the only safe option.
Do not add any ingredients beyond those given in the tested recipe. It is safe to double or halve a salsa recipe, but it is not safe to add other vegetables. If you want to add things like black beans or corn to your salsa, do it just before serving. Adding thickeners and ingredients not included in the recipe before canning can result in an unsafe product. If your salsa is too runny, you can add a thickener like cornstarch or tomato paste after opening the jar, or you can just pour off some of the liquid before serving.
One typed of pepper may be substituted for another. However, do not increase the amount of them in the recipe. Red, yellow or white onions may be substituted for each other; still do not increase the total amount of onions in any recipe. The amount of dried herbs and spices can be altered. It is not safe to increase the amounts of fresh herbs or garlic before canning because they affect the acidity level and produce an unsafe salsa. For stronger flavor, add fresh herbs, garlic, and spices just before serving. Follow these tips to ensure safely canned salsa!
Only pint jars are approved for home-canning salsa. You cannot use quart jars when it calls for pint jars because there is not a processing time tested for quarts.
Follow Research-Based Recipes
When canning your tomatoes or salsa, it is crucial 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!
For approved tomato, salsa, and many more home-preserved foods, recipes, visit the UW Nutrition and Food Safety website at https://uwyoextension.org/uwnutrition/category/food-preservation.
Other references include the “Ball Complete Book of Home Preserving,” the “So Easy to Preserve Book” from the University of Georgia, and the “USDA Complete Guide to Home Canning.”
Written by Vicki Hayman, MS, University of Wyoming Extension Nutrition and Food Safety Educator
Sources:
- Complete Guide to Home Canning, 2015 revision, https://nchfp.uga.edu
- United States Department of Agriculture, www.usda.gov
- University of Wyoming Extension Food & Nutrition Website, https://uwyoextension.org