Remember to acidify tomatoes when canning

Avoid botulism and spoilage by always acidifying tomatoes when preserving them at home.

Tomatoes are one of the most common vegetables canned at home in the United States. Tomatoes are also one of the most commonly spoiled home-canned products. This spoilage often is due to the tomatoes not being acidified. 

The primary reason tomatoes need to be acidified is to prevent botulism poisoning and other bacterial concerns from occurring. The bacterial spores that cause botulism are unable to produce toxins when in a high acid environment. Normally, tomatoes have a pH level below 4.6. However, some tomatoes may have a pH level above 4.6 or even as high as 4.8. Research has shown there are several reasons why it has become necessary to acidify tomatoes.

The reasons for a reduced acidity level in tomatoes include damage or decay caused by bruises, cracks, blossom end rot, insects and overripening. Tomatoes that are grown in the shade or ripened in shorter sunlight hours or ripened off the vine tend to have a lower pH level than those tomatoes ripened in the sunlight on the vine.  Another reason is tomatoes that are harvested from dead vines tend to be considerably less acidic than tomatoes harvested from healthy vines.

Decayed and damaged tomatoes and tomatoes harvested from frost-killed or dead vines should never be home-canned. To home-can tomatoes using a boiling water technique, select only disease-free, preferably vine-ripened firm fruit.

Michigan State University Extension recommends tomatoes be acidified using 1 tablespoon of bottled lemon juice per pint jar of tomatoes.

Bottled lemon juice can be used to acidify tomatoes: For quart jars of tomatoes, use 2 tablespoons of bottled lemon juice per quart. Bottled lemon juice is used because the bottled lemon juice is standardized to a specific pH level. The lemon juice is added directly to the jar before filling the jar with the tomatoes. If the finished product tastes too acidic, before serving add a little sugar to offset the acid taste.

Citric acid may also be used to acidify tomatoes: Use ¼ teaspoon of citric acid per pint jar of tomatoes. For quart jars of tomatoes use ½ teaspoon of citric acid.

Directions on how to can tomatoes may be found at United States Department of Agriculture Guide to Home CanningClick here a free copy of Using, Preserving, and Storing Tomatoes.

To safely can tomatoes at home using the boiling water technique, remember to acidify!

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