How to Can Tomatoes the Right Way

Juicy, sweet tomatoes are a staple of summer—and if you grow the fruit at home (or love to stock up at the farmers' market), you probably know what it's like to have an influx of tomatoes in your kitchen. Canning tomatoes is an excellent method for preserving your haul, as the finished product can be used in iconic dishes all year round, from chunky chili to homemade pizza.

The canning process requires specific steps to ensure the tomatoes are safe for long-term storage. Learn how to can tomatoes with our comprehensive guide, plus how long home canned tomatoes last. 

Best Tomatoes for Canning

The best tomato varieties for canning are roma, plum, and paste tomatoes, says William Dissen, chef at The Market Place restaurant in Asheville, N.C. These types of tomatoes have lower amounts of water, which will help them hold up to the high temperature of hot water canning.

Regardless of the variety, it's imperative to use tomatoes that are at their peak ripeness, disease-free, vine-ripened, and firm, says Tracey Brigman, EdD, MS, RDN, LD, a clinical associate professor and associate director for National Center for Home Food Preservation at the University of Georgia. Never use tomatoes from vines that are dead or destroyed by frost, which may carry harmful or spoilage microorganisms, according to the experts at the University of Minnesota.

How to Prepare Tomatoes for Canning

Tomatoes need to be blanched and peeled before canning can begin. According to Brigman, the blanching step will assist with the peeling process. On that note, it's important to remove the peels when the recipe calls for it, as the peel can be bitter and tough. Additionally, "much of the bacteria lives on the skin of tomatoes, so it’s often removed for safety reasons," says Brigman. The peel can also interfere with the heating and cooling process required to destroy microorganisms, she says.

If the recipe instructs you to cut the tomatoes before canning, be sure to do so. According to Brigman, the recipe's processing time—which will ensure the tomatoes are shelf-stable and safe to eat—is determined by thickness and size (among many other factors), so it's important to follow the listed steps. Similarly, if the recipe involves boiling the tomatoes, pay attention to the time listed. "If you boil them for too long, it will [negatively] affect the quality of your end product," Brigman says.

How Long to Cook Tomatoes for Canning

According to the National Center for Home Food Preservation, tomatoes can be canned raw or boiled. The standard time for boiling tomatoes for canning is five minutes, but again, be sure to follow the time listed in your specific recipe.

Recipe for Canning Tomatoes

When canning tomatoes, the exact process will vary between recipes. Always follow a recipe that has been tested by experts to ensure a safe product. The canned tomatoes recipe method used here includes water bath canning:

1. Bring a pot of water to a boil. Meanwhile, prepare an ice bath.
2. Wash and drain the tomatoes, then cut an X in the bottoms. 
3. Blanch the tomatoes for 15 seconds, then submerge in the ice bath. Remove the tomatoes and peel off the skins.
4. Place tomatoes in a saucepan, cover with water, and bring to a boil. Cover and simmer for 5 minutes.
5. Fill each jar halfway with tomatoes. For pint jars, add ½ teaspoon salt and ¼ teaspoon citric acid. For quart jars, add 1 teaspoon salt and ½ teaspoon citric acid.
6. Add tomatoes until the jar is full, pressing down to pack.
7. Spoon hot cooking water over tomatoes, leaving about ½ inch headspace. This will help the rubber gasket seal during the canning process, says Dissen.
8. Slide a nonmetallic spatula between tomatoes and jar, then press on tomatoes to release air bubbles. Repeat 2 or 3 times.
9. Wipe the rim and threads of each jar with a clean, damp cloth.
10. Screw the lid onto the jar, just until you feel resistance.
11. After filling each jar, place it on the raised rack in your boiling-water canner. The water should be simmering.
12. When all the jars are filled and placed on the rack, lower the rack into the canner. Add boiling water, if needed, to ensure the water level covers lids by 1 to 2 inches.
13. Place the lid on the canner. Bring water to a rolling boil, then reduce to a gentle but steady boil for 40 minutes (or 45 minutes for quarts) to process.
14. After the required time, turn off the heat and remove the canner lid. Let cool for 5 minutes before removing the jars.
15. Set them upright on a dry towel or cooling rack, about 1 to 2 inches apart. Do not retighten the bands. Let cool for 12 to 24 hours.
16. After the jars have cooled, test the seals by pressing on the center of each lid. The seal is set if the lid is concave and you can't lift it off. If the lid pops back up, you'll need to repeat the process.

Acidification in Tomato Canning

Since there are so many types of tomatoes, the fruit can range between high and low acidity, says Brigman. Therefore, it’s essential to acidify the tomatoes to prevent the growth of Clostridium botulinum (C. botulinum), the bacterium that releases the toxin that causes botulism.

To do this, add 1 tablespoon bottled lemon juice or ¼ teaspoon citric acid per pint of tomatoes (or 2 tablespoons of bottled lemon juice or ½ teaspoon of citric acid per quart), as instructed by the experts at the National Center for Home Food Preservation. These ingredients will lower the pH level (i.e., make it more acidic) to make the tomatoes safe for canning in a water bath or pressure canner, says Dissen.  

If you don't have lemon juice or citric acid, 4 tablespoons of 5 percent acidity vinegar per quart can also be used. The only catch: Vinegar can negatively alter the flavor of your tomatoes. Additionally, some vinegars on the market are only 4 percent acidity, so it's crucial to check the label to ensure it's at least 5 percent acidity, says Brigman.

How Long Do Canned Tomatoes Last?

When properly canned and stored in a cool, dark area, canned tomatoes will last for quite some time. Brigman recommends using them within one year for best results.

After opening the jar, canned tomatoes should be refrigerated and used within three to four days, says Brigman.