MSU Extension Safe Food & Water

Tomatoes are available in gardens and farm markets all over the state right now. During food preservation classes, a common question related to tomatoes is, “Do we have to add lemon juice to our tomatoes?”

The short answer is, yes. It is critical when home canning tomatoes, whether they are whole, crushed or juiced, to acidify them during the canning process by adding bottled lemon juice or citric acid. But why?

The acidity of a tomato is considered borderline between a high- and low-acid food. Tomato varieties have been changed through the years and as a result, many now have milder flavor and lower acidity than 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 bottled lemon juice or citric acid lowers the pH of all tested varieties enough to allow for the safe process of water bath canning. Acidifying all whole, crushed or juiced tomatoes now is recommended because this ensures the safety of the canned product after processing in a water bath canner (and for a safe short process in a pressure canner). These tomatoes must be acidified whether you are using a 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 ½ teaspoon of citric acid per quart of tomatoes. For pints, use one tablespoon bottled lemon juice or ¼ teaspoon citric acid. Bottled 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 freshly squeezed. The bottled lemon juice has a standardized acidity level, while fresh squeezed juice has varying levels so cannot be used. 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.

Acidifying tomatoes when recommended will give you the confidence in knowing you have preserved safe tomatoes to enjoy all winter long.

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 methods have changed over the years, and it is critical to use current methods to have a safely preserved product for you to consume. Recommended resources include MSU Extension Michigan Fresh, the USDA Guide to Complete Home Canning, National Center for Home Food Preservation, So Easy to Preserve book, or a current Ball Blue Book.

For more on home food preservation enroll in MSU Extension’s online Home Food Preservation course or join a free, online Preserving MI Harvest class. You can also follow us on Think Food Safety for food preservation tips and information and easy access to our online classes, and watch our new food preservation videos.