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Extension > Food > Food Safety > Preserving and Preparing > Tomatoes and Salsa > Add acid to tomatoes before processing

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Tomatoes and Salsa

Add acid to tomatoes before processing

Carol Ann Burtness

Today, our current varieties of tomatoes are not as high in acid as they used to be. Today, researchers have found that new tomato varieties; stressful growing conditions; or over-mature fruit may affect acid levels. Other factors that affect the acidity level of tomatoes include adding low-acid ingredients to tomatoes such as onion and peppers; making juice versus tomato solids; and the canning process itself. Because many factors impact the acidity level of tomatoes and may support the growth of Clostridium botulinum, USDA recommends adding acid to all home-canned tomatoes and tomato products.

Today’s canning recommendations require that acid be added to all canned tomato products even if they are pressure canned. Horticulture researchers have concluded the acidity of heirloom tomato plants is no different from the non-heirloom varieties. In fact, there are some heirloom varieties that are more low-acid than hybrid varieties. As a result, the same acidification recommendations apply for canning heirloom tomatoes


Acid can easily be added directly to the jars before filling with tomatoes. Added acid can be either citric acid or bottled lemon juice. Citric acid is available where canning supplies are sold or ordered online.

Added acid can be either
citric acid or bottled lemon juice.


Add acid to all tomatoes
Acid Effect Amount
Citric acid Little change in flavor 1/2 tsp/quart
1/4 tsp/pint
Bottled lemon juice Easy to use 2 Tbsp/quart
1 Tbsp/pint
Vinegar (5% acidity) Noticeable flavor change 4 Tbsp/quart
2 Tbsp/pint

For more information, check out National Center for Food Preservation


Home Food Preservation Newsletter. July 2012. University of Minnesota Extension.

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Revised by Suzanne Driessen 2017

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