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Tomatoes differ in acidity depending on the variety and growing conditions. Although tomatoes usually are considered an acid food, some are now known to have pH values slightly above 4.6. Therefore, if they are to be canned as acid foods, they must be acidified to a pH of 4.6 or lower with bottled lemon juice or citric acid. Properly acidified tomatoes are acid foods and can be safely processed in a boiling-water bath canner.
To ensure safe acidity in whole, crushed or juiced tomatoes, the USDA/WSU recommends adding acid in the form of bottled juice (never fresh) or citric acid power in the following increments:
1 tablespoon bottled lemon juice per pint
- or -
¼
teaspoon citric acid powder per pint
2 tablespoons bottled lemon juice per quart
- or -
½ teaspoon citric acid powder per quart
The acid may be added at the bottom of the pack or at the top. Always put the acid directly in the jar and not into the batch. The movement of the contents during processing will distribute it.
Some flavor changes may occur with the addition of the acid. The addition of sugar, (1 teaspoon per pint, 2 teaspoons per quart), can offset the tartness. You may add salt to enhance the flavor at a rate of ½ teaspoon per pint and 1 teaspoon per quart. Salt is added for taste only, and does not aid in preservation.
ADDING ACID IS NOT A CRUTCH! Always use current USDA/WSU recommendations for processing times and methods. Never take shortcuts or reduce processing times.
In 1998, the USDA and Washington State University changed the processing times for water-bath canning and pressure canning of tomatoes. Check with your local Extension Office for the current processing times.
For further information contact Washington State University Cooperative Extension Whatcom County at (360) 676-6736. Low cost publications are available for purchase at the Whatcom County Cooperative Extension Office. Volunteers are available during the canning season to answer your questions.
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