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How to Can Tomatoes

Medically Reviewed by Poonam Sachdev on May 31, 2022

When you think of tomatoes, you probably assume they're a vegetable. However, botanically they're considered a fruit. It usually doesn't make a difference how you think of them, but it does if you plan to can them. Since tomatoes are high in acid, it helps to preserve them by water bath canning, which entails adding a little lemon juice or vinegar. Of course, you can still pressure can them if you'd prefer. Tomatoes are some of the most versatile foods to can, so chances are there's a method and recipe that will work for you. 

How Do You Choose the Best Tomatoes for Canning?

Choose fresh, firm tomatoes that are vine-ripened. Decayed or damaged tomatoes and those harvested from dead or frost-killed vines are not suitable for home canning. Some other growing conditions can also reduce the acidity of tomatoes, including those listed below.

  • Cracks
  • Blossom end rot
  • Insects
  • Overripening 
  • Growing in the shade
  • Being ripened off the vine

How to Acidify Tomatoes for Canning

To ensure your tomatoes have enough acid to prevent botulism, you need to add acid to them before canning. You should do this no matter how you're canning your tomatoes or what recipe you're using. For each quart of tomatoes, add two tablespoons of bottled lemon juice or one-half teaspoon of citric acid. For each pint of tomatoes, add one tablespoon of bottled lemon juice or one-fourth teaspoon of citric acid. 

You can also use four tablespoons of a 5 percent acidity vinegar per quart instead of lemon juice or citric acid. However, vinegar may change the flavor of the tomatoes. If you want to counteract the acid taste, you can add sugar. Your acid of choice can be added directly to the jars before you fill them with tomatoes. 

Canning Crushed Tomatoes

You'll need around 22 pounds to can 7 quarts of tomatoes or 14 pounds for 9 pints. 

Wash your tomatoes well and then dip them in boiling water until their skins split, usually in 30 to 60 seconds. Dip them in cold water and cut out the cores. Cut away any damaged or bruised areas and quarter the tomatoes. In a large pot, quickly heat and crush about one-sixth of the tomatoes. Heat the crushed tomatoes until boiling, stirring them often to prevent sticking. Gradually add the remaining tomatoes without crushing them. Boil all of the tomatoes gently for five minutes. 

Add the acid to your jars and add one teaspoon of salt per quart if desired. Fill the jars with hot tomatoes immediately, leaving one-half-inch headspace. Put on lids and process as follows: 

Boiling water canner. Process pints or quarts in a boiling water canner for the times listed below based on your altitude.

  • Altitude 0-1000 feet: Pints 35 minutes, quarts 45 minutes 
  • Altitude 1001-3000 feet: Pints 40 minutes, quarts 50 minutes
  • Altitude 3001-6000 feet: Pints 45 minutes, quarts 55 minutes 
  • Altitude above 6001 feet: Pints 50 minutes, quarts 60 minutes

Weighted-gauge pressure canner. Process at the pressure and time listed below based on your altitude.

  • Altitude 0-1000 feet: Pints or quarts 20 minutes at 5 pounds of pressure, 15 minutes at 10 pounds of pressure, or 10 minutes at 15 pounds of pressure
  • Altitude above 1001 feet: Pints or quarts 20 minutes at 10 pounds of pressure, or 15 minutes at 15 pounds of pressure

Dial-gauge pressure canner. Process at the pressure and time listed below based on your altitude.

  • Altitude 0-2000 feet: Pints or quarts, 20 minutes at 6 pounds of pressure, or 15 minutes at 11 pounds of pressure
  • Altitude 2001-4000 feet: Pints or quarts, 20 minutes at 7 pounds of pressure, or 15 minutes at 12 pounds of pressure
  • Altitude 4001-6000 feet: Pints or quarts, 20 minutes at 8 pounds of pressure, or 15 minutes at 13 pounds of pressure
  • Altitude 6001-8000 feet: Pints or quarts, 20 minutes at 9 pounds of pressure, or 15 minutes at 14 pounds of pressure

Tips for Preserving Tomatoes

Tomatoes are the most commonly canned food and can be preserved as juice, sauce, salsa, ketchup, and purees. However, it's important to follow safety guidelines to lower the risk of botulism in your home-canned tomatoes. 

Use the right tomatoes for the right product. Regular tomatoes are best for juice and canned tomatoes. Italian and plum tomatoes work well for sauce, ketchup, salsa, and purees. You can mix tomatoes with good results as well. 

Don't use unsafe canning methods. Pouring hot tomatoes into a jar and waiting until the lid seals and pops isn't a safe canning method. The contents haven't been heated enough to kill harmful microorganisms. You should avoid oven canning and using powders such as aspirin for the same reason. 

Use the right-sized jar. Don't can tomato juice or other tomato products in half-gallon jars. Always use quart or pint-sized jars. 

Don't add extra ingredients to recipes. Always use a tested recipe from a trusted source. You shouldn't add thickeners to tomato products before canning them. Measure out ingredients accurately and don't add extra garlic, peppers, onions, or other low-acid ingredients to your tomatoes. However, it is safe to omit low-acid ingredients from tomato recipes. If you hate onions, feel free to leave them out. 

Make sure you process tomatoes long enough. You should always follow the processing times for your canning method and altitude. Botulism thrives in a low-acid environment with a lack of air. Over 90% of foodborne botulism can be traced to home-canned foods, so you want to make sure you wash your food and utensils thoroughly, add acid to your tomatoes, and follow the directions for your recipe. If you're adding meats or other low-acid ingredients to your tomato sauce, you may need to process it in a pressure canner. 

Show Sources

SOURCES:

Colorado State University Extension: "Canning Tomatoes and Tomato Products."

National Center for Home Food Preservation: "Crushed Tomatoes (with no added liquid)," "Selecting, Preparing and Canning Tomatoes."

Penn State Extension: "Canning Tomatoes: Do's and Don'ts."

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