Cooks Note: This recipe is included for historical reference only. The USDA no longer recommends oven canning. However, a canning jar is being produced from a new, stronger glass called Hercules glass, and steam ovens are now being manufactured for home use. It may be possible to return to this method of canning in the future after further testing for safety is performed. We do not recommend this method of canning currently. However, the same recipe may be used for processing in a boiling water bath for 40 minutes (pints) or 45 minutes (quarts).

To ensure safe acidity in 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. Acid can be added directly to the jars before filling with product. Add sugar to offset acid taste, if desired. Four tablespoons of a 5 percent acidity vinegar per quart may be used instead of lemon juice or citric acid.