Home canning tomatoes is a great way to preserve them for later use. Proper methods, high- ingredients and awareness of acidity levels are critical for a safe product.
Always follow a research-based recipe. We recommend using The National Center for Home Food Preservation.
Choose only high-quality tomatoes
Choose fresh, vine-ripened tomatoes that are at their peak ripeness.
Over-ripe tomatoes are less acidic. The acidity level in tomatoes varies throughout the growing season. Tomatoes reach their highest acidity when they are still green and decrease in acidity until they reach their lowest acidity as they mature.
Do not can damaged tomatoes or those from dead or frost-killed vines. These tomatoes may have harmful pathogens. The canning process time may not be enough to kill disease organisms. This could lead to a product that spoils and is unsafe to eat.
Before processing: Add acid to all tomatoes
Because many factors impact the acidity level of tomatoes, the USDA recommends adding acid to all home-canned tomatoes and tomato products regardless of the canning method.
A high acid level (pH of 4.60 or less) prevents the growth of Clostridium botulinum bacteria, which produces a toxin that, when eaten, causes botulism.
- Treat heirloom tomato varieties the same as any other tomato. The acidity of heirloom tomatoes is no different from the non-heirloom varieties. Some heirloom varieties are lower-acid than hybrid varieties. Therefore, the same acidification recommendations apply for canning heirloom tomatoes.
Factors impacting acidity
The acidity level of tomatoes can be affected by many factors, including:
- The variety of tomatoes
- Stressful growing conditions
- Over-mature fruit
The acidity level of canned tomato products can be affected by:
- Adding low-acid ingredients to tomatoes (such as onion and peppers)
- Making juice versus tomato solids
- The canning process itself
Acid options: Citric acid, lemon juice and vinegar
Citric acid
- Citric acid is available wherever canning supplies are sold.
- Canning supply companies like Mrs. Wages and Ball have a powder form of citric acid.
- Be sure the product you buy is food grade.
Vinegar
- All vinegars will noticeably change the flavor of your end product.
- You can add a small amount of sugar to help offset the flavor.
Lemon and lime juice
- Use commercially bottled juice.
- Don't use freshly squeezed lemon juice. The acidity level varies and there is a chance of contaminating the juice from the rind.
- You can safely use bottled lime juice instead of bottled lemon juice.
- Bottled lemon and lime juice contains sulfites. If you or family members have a sulfite sensitivity or allergy, alternative options are:
- Citric acid
- Vinegar
- Frozen lemon juice (not lemonade) from the grocery store. Use the same amounts of frozen juice as bottled lemon juice.
Quantity of added acids
| Type of acid | Impact | Amount per quart | Amount per pint |
|---|---|---|---|
| Citric acid | Little change in flavor | 1/2 teaspoon | 1/4 teaspoon |
| Vinegar (5% acidity) | Noticeable flavor change | 4 tablespoons | 2 tablespoons |
| Bottled lemon juice | Easy to use | 2 tablespoons | 1 tablespoon |
Never add thickener before canning tomato products
Never, under any circumstances, add a thickening product before canning.
Thickening products like flour, cornstarch, rice, pasta or cream will change the acidity level of your tomatoes. They can create a thick product that does not allow good heat penetration. As a result, adding thickeners before canning may result in an unsafe product.
How to produce a thicker tomato product
- Try using Italian plum-style or paste tomatoes vs. large slicing tomatoes.
- Thicken salsas by adding tomato paste or by draining off some of the liquid after you chop the tomatoes.
Are you ready to process your food?
The processing time is determined by:
- Jar size
- Pack style
- Headspace
- Elevation
Ideas for canning tomatoes
Reviewed in 2026