Add Acid to Tomatoes Before Processing
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.
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.
citric acid or bottled lemon juice.
- Add 2 tablespoons of bottled lemon juice or 1/2 teaspoon of citric acid per quart of tomatoes.
- For pints, use 1 tablespoon of bottled lemon juice or 1/4 teaspoon of citric acid.
- Instead of the lemon juice or citric acid, vinegar can be used, but it will cause a more noticeable flavor change. Add 4 tablespoons of vinegar per quart or 2 tablespoons of vinegar per pint.
NOTE: Do not use freshly squeezed lemon juice because the acidity level varies and there is a chance of contaminating the juice from the rind. Also, tomato canning tablets that may be found on the market should not be used because they are ineffective.
Add acid to all tomatoes
|Citric acid||Little change in flavor||1/2 tsp/quart
|Bottled lemon juice||Easy to use||2 Tbsp/quart
|Vinegar (5% acidity)||Noticeable flavor change||4 Tbsp/quart
For more information, check out National Center for Food Preservation
- Adding Acid to Home-Canned Tomatoes
- How to Freeze Homemade Stewed Tomatoes
- To Thicken or Not to Thicken Canned Tomato Products
Peer reviewed by Suzanne Driessen 2015