Planning to Can Tomatoes

With tomato season around the corner, one safe method for preserving tomatoes is water bath canning or pressure canning. Unlike freezing, more supplies are needed for canning, as well as shelf space in a cool dark place. Whether it’s making salsa, sauce, ketchup, juice, paste, or canning crushed, whole, or halved tomatoes, it’s crucial to follow specific rules to make sure the tomato product remains at best quality and is safe to eat later.

When canning, always use a scientifically tested recipe. Safe recipes can be found through the National Center for Home Food Preservation, the USDA’s Complete Guide to Home Canning, or by contacting the local Extension office. One of the main reasons why new, homemade recipes cannot be used for canning is because of the chance of the canned food producing Clostridium botulinum, making the deadly botulism toxin. The acidity, temperature, and processing time play key roles in preventing the formation of botulism. However, if there is a strong desire to use a home recipe for canning, there are laboratories who will test the product for safety. Visit for laboratories or contact the local Extension offices to find more options.

Along with using a safe recipe for canning tomatoes, do not replace pressure canning for water bath canning or vice versa if it only suggests one method for processing in the recipe. Most tomato recipes that incorporate meat or vegetables require pressure canning. Additionally, the acid must be added to tomatoes regardless of processing method to control the pH and reduce the risk of botulism poisoning. Add one tablespoon of bottled lemon juice, one-fourth teaspoon citric acid, or two tablespoons vinegar per pint. For quarts of tomato products, add two tablespoons bottled lemon juice, one half a teaspoon citric acid, or four tablespoons of vinegar. The lemon juice used must be bottled and not fresh, since lemon acidity can vary. Vinegar can affect the flavor of the tomato product; this can be offset by the addition of sugar.

Do you want to make substitutions in a canned salsa recipe? Changing the type of onion or pepper is safe, but the amount cannot be changed. Herbs and spices in canned salsa recipes can be replaced or left out, as this does not affect the safety of the recipe. For the acidity, it is safe to substitute the bottled lemon juice for vinegar, but not vinegar for lemon juice. One is more acidic than the other. Homemade canned salsa is a delicious and fresh addition to any meal, plus the satisfaction of using the home garden or local ingredients and knowing exactly what is in the product.

Have additional questions about canning tomatoes? Join University of Illinois Extension Nutrition and Wellness Educators on July 22, from 1 pm to 2 pm online as they focus on canning, freezing, drying, tomatoes for the last of their fill your pantry webinar series. Call the extension office to sign up or register yourself at Miss a webinar? The webinars are available at under the recorded webinar tab.

Chile Salsa - Makes 6 to 8 pints

10 cups peeled, cored and chopped tomatoes

6 cups seeded, chopped chile peppers

4 cups chopped onions

1 cup vinegar, 5% acidity

3 teaspoons salt

½ teaspoon black pepper

1. Wash hands with soap and water.

2. Combine all ingredients in a large saucepan and heat, stirring frequently, until mixture boils. Reduce heat and simmer for 10 minutes, stirring occasionally.

3. Fill clean, hot pint jars (preferably wide-mouth) with salsa, leaving 1/2-inch headspace. Remove air bubbles and adjust headspace. Wipe rims of jars with a dampened clean paper towel; adjust two-piece metal canning lids—process pints for 15 minutes in a boiling water bath. Adjust processing time to 20 minutes for altitude from 1,001-6000 ft. and 25 minutes above 6000 ft. Let cool, undisturbed, 12-24 hours, and check for seals. Source: National Center for Home Food Preservation  


Questions about food safety, nutrition, food preservation, or looking for recipes? Contact the local University of Illinois Extension office.

Source: Lisa Peterson, Extension Educator, Nutrition and Wellness