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Tomato Do's and Don'ts

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Posted: August 5, 2012

Tomatoes are one of the most commonly canned vegetables. Because many canning procedures for tomatoes have been handed down from generation to generation, there are many canning recipes that are inadequate to kill all spoilage microorganisms.

Canning recommendations for tomatoes have changed over the years. Although tomatoes have a tangy acidic taste, they actually do not contain as much acid as fruit. Because tomatoes are borderline between high and low acid foods, certain precautions must be taken to can them safely. Below are do's and don't to keep in mind when processing tomatoes and tomato products.

Do use high quality tomatoes. Some growing conditions may cause the tomatoes to be unsafe to can even when the tomatoes look fine. Tomatoes with blight and those from dead or frost-killed vines may be lower in acidity and are more likely to carry bacteria.

Do acidify the tomatoes by adding bottled lemon juice or citric acid to each jar before processing. Place 2 tablespoons bottled lemon juice or ½ teaspoon citric acid crystals in the bottom of each quart jar before filling with the tomato product. Use half those amounts when canning in pint jars. This will assure a safe acidity level. 

Other tomato products should also be acidified. Some catsup and barbecue sauces do not need to be acidified because they contain large amounts of vinegar that provides the needed acidity. If in doubt, add the lemon juice.

Do process long enough. Processing times for tomatoes have increased over the years. Processing time depends upon the method of pack and added ingredients. Quarts of tomato juice, tomato vegetable juice blend, and crushed hot pack tomatoes should be processed 45 minutes in a boiling water bath. Hot or raw pack whole or halved tomatoes packed in water only require 45 minutes of processing while the same tomatoes packed in tomato juice or without added liquid require 85 minutes of processing time. Tomatoes may also be processed in a pressure canner. In fact, tomato products with added vegetables or meat require pressure canning. 

Do match the type of tomato to the product being canned. Regular tomatoes work well for juice and canned tomatoes. Italian and plum type varieties are good for making sauce, salsa, catsup, and purees. The two types can be mixed.

Do follow the same directions for canning low-acid tomatoes or yellow tomatoes as are recommended for canning regular tomatoes. Although low-acid tomatoes don’t taste as sour, their acidity is masked by the natural sweetness of the variety; so no changes are needed in the recipe for safety.  

Do not can using the open kettle method. That means do not just heat the tomatoes or tomato product and pour the hot product into the jars, add the lids, and wait for the lids to “pop” without any further processing. Even though the jars may seal, the contents inside the jars have not been heated adequately to destroy harmful spoilage organisms. Other unsafe methods include oven canning and the use of so-called canning powders. Aspirin belongs to this last category.

Do not can tomato juice in half-gallon jars. Half-gallon jars are only suitable for canning apple or grape juice. Use quart or smaller jars for canning all tomato products.

Do not make up your own recipes for canning salsa, spaghetti sauce, pizza sauce, etc. All these foods have added low acid ingredients for flavor. Use up-to-date scientifically research based recipes.

Do not add low acid ingredients such as peppers, onion, garlic, etc. for flavor unless using a scientifically tested recipe. Do not add extra of these ingredients in a tested recipe.  Add no more than three cups in any combination of finely chopped celery, onions, carrots, and pepper for each 22 pounds (the amount for seven quarts) of tomatoes when making tomato-vegetable juice blends.

Do not add thickeners or milk to tomatoes or tomato products before processing. Instead, add the ingredients to make stewed tomatoes or tomato soup when you are ready to serve them.  

For additional information and more recipes for canning tomatoes visit http://extension.psu.edu/food-safety/food-preservation/safe-methods/