Elizabeth L. Andress, Ph.D.
National Center for Home Food Preservation
Just as the varieties of tomatoes in the markets keep changing and increasing in number, it is important to remember we have variety in the directions for canning tomatoes.
Home canned tomatoes may prepared in a ready-to-use crushed format or left whole or halved. But the latter choices can be processed in a variety of ways, also. Whole or Halved Tomatoes may be canned with water to cover, in tomato juice, or with no added liquid. The crushed tomatoes are a hot pack only, while the no-added-liquid version of canned tomatoes is a raw pack only. It is very important to use to a canning process time that matches up with the preparation directions for filling your jars.
Here is a summary of the variety in tomato canning directions that USDA has to offer as the only safe alternatives:
Tomato products offer many more options for home canning of tomatoes: spaghetti sauce, with or without meat, ketchups, tomato and vegetable blends, etc.
No matter how you choose to can your tomatoes, all steps in preparing and cooking the foods still need to be followed for the process time(s) printed with them. The process times are very different for tomatoes packed in water compared to tomato juice or without added liquid. For many of these tomato products, there are canning options for both boiling water and pressure canning available in our directions.
In the case of these tomato products with both options, the pressure processing still requires acidification in these products. The pressure options only provide the same amount of heat to the product as the boiling water processes. Just because pressure is used to decrease the process time, the canning process is not the same as one to destroy spores of Clostridium botulinum as you would expect for low acid foods.
Tomatoes are borderline in pH between acid and low acid foods, so the USDA preparation directions for these products call for acidification to allow a less severe heat treatment than would be required without it. To ensure safe acidity in 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. Acid can be added directly to the jars before filling with product; in fact, this is recommended to be sure you get the acid in each and every jar. Sugar may be added to offset an acid taste, if desired, but the acid cannot be decreased to taste. (Four tablespoons of a 5 percent acidity vinegar per quart may be used instead of lemon juice or citric acid. However, vinegar may cause undesirable flavor changes.)
Canning your tomatoes does not have to be too complicated, if you simply use reliable, research-based printed directions for preparing and processing your food. The National Center for Home Food Preservation has recommended directions for canning tomatoes and tomato products under "How do I"...."Can"....."Canning Tomatoes and Tomato Products," at http://www.uga.edu/nchfp/how/can3_tomato.html.
Elizabeth L. Andress is an Extension Food Safety Specialist with the Cooperative Extension Service, Department of Foods and Nutrition, College of Family and Consumer Sciences, The University of Georgia, Athens.