Acidifying your home canned tomatoes

The question still remains: Do you need to add lemon juice to your home canned tomatoes?

Tomatoes are available in gardens and farm markets all over the state right now. During food preservation classes this summer, one question related to tomatoes was asked at almost every class I instructed, “Do we have to add lemon juice to our tomatoes?” Along with those asking the lemon juice question, there were many participants who had never even heard about the lemon juice recommendation. The following information will help you understand that “yes” you must add lemon juice to your tomatoes and why.

It is critical when home canning tomatoes, whether they are whole, crushed or juiced to acidify them during the canning process. The acidity of a tomato is considered borderline between high and low acid foods.

Tomato varieties have been changed through the years and as a result, many now have milder flavor and lower acidity than the in the past. Testing has shown that some current tomato varieties have pH values at or above pH 4.6; a few have values of pH 5 or even higher. Adding the recommended amount of lemon juice (or citric acid) lowers the pH of all tested varieties enough to allow for safe boiling water bath canning. Acidifying all tomatoes now is recommended because it allows for safe processing in a boiling water bath canner (and for a safe short process in a pressure canner). To ensure their safety after being preserved, they must be acidified as part of the food preservation process and they must be acidified whether you are using a boiling water bath canner or pressure canner.

The acidification process is quite simple. To acidify whole, crushed or juiced tomatoes, add two tablespoons of bottled lemon juice or 1/2 teaspoon of citric acid per quart of tomatoes. For pints, use one tablespoon bottled lemon juice or 1/4 teaspoon citric acid. The lemon juice can be added directly to the jars before filling with the tomato product or can be added after filling. Just make sure to add the lemon juice to each jar and to follow the recommended amounts precisely. Bottled lemon juice must be used, not fresh squeezed. The bottled lemon juice has a standardized acidity level, with fresh squeezed the level can vary. Sugar may be added to offset an acid taste after opening the jars that have been processed and sealed, if desired, but the acid cannot be decreased prior to canning.

Michigan State University Extension also reminds home food preservers to always use current, research based recipes when canning tomatoes as well as any other produce. Recommendations and preservation processes have changed through the years and it is critical to use current methods in order to have a safely preserved product for you to consume. Resources that are recommended include: MSU Extension Michigan Fresh, National Center for Home Food Preservation, So Easy to Preserve book, Ball Blue Book (newer than 2000) and the USDA Guide to Complete Home Canning.

Acidifying tomatoes when recommended and using current food preservation recipes will give you the confidence in knowing you have preserved safe tomatoes.

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