Minidoka County

• Select disease-free, preferably vine-ripened, firm tomatoes for canning. Avoid overripe tomatoes.
• To ensure safe acidity in whole, crushed or juiced tomatoes, add 2 tablespoons of bottled lemon juice or 1/2 teaspoon of citric acid per quart of tomatoes. For pints, add 1 tablespoon bottled lemon juice or 1/4 teaspoon citric acid.
• Freezing is a safe, easy alternative to home canning. Frozen tomatoes and tomato products do not need added acid.

Tomatoes are the most widely home-canned product in the United States. They also are one of the most commonly spoiled home-canned products. The canning processes recommended in this fact sheet are the result of USDA research on safe home-canning procedures for tomatoes and tomato products.

Tomato Acidity

Although tomatoes are considered a high-acid food (pH below 4.6), certain conditions and varieties can produce tomatoes and tomato products with pH values above 4.6. When this happens, the product must be canned in a pressure canner as a low-acid product or acidified to a pH of 4.6 or lower with lemon juice or citric acid.

Research has found several conditions that can reduce the acidity of tomatoes. These include decay or damage caused by bruises, cracks, blossom end rot or Insects, and over-ripening. Tomatoes grown in the shade, ripened in shorter hours of daylight, or ripened off the vine tend to be lower in acidity than those ripened in direct sunlight on the vine. Also, tomatoes attached to dead vines at harvest are considerably less acidic than tomatoes harvested from healthy vines. Decayed and damaged tomatoes and those harvested from frost-killed or dead vines should not be home canned.

To ensure safe acidity in whole, crushed or juiced tomatoes, add lemon juice or citric acid when processing in a boiling water bath. Add 2 tablespoons of bottled lemon juice or 1/2 teaspoon of citric acid per quart of tomatoes. For pints, use 1 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 the taste, if desired. Four tablespoons of a 5 percent acidity vinegar per quart can be used instead of lemon juice or citric acid. However, vinegar may cause undesirable flavor changes.

Process Carefully to Avoid Spoilage

The most common reasons for spoilage in home-canned tomato products are under processing and incomplete seals. Tomatoes that have not been processed long enough to destroy molds and heat-resistant bacteria may spoil during storage. One of the common spoilage organisms, Bacillus coagulans, is very heat resistant and causes flat-sour spoilage. The jar lid may still be sealed and the product may appear normal, but the tomatoes will smell sour because of lactic acid produced by the growth of B. coagulans in the product. Never use tomatoes or tomato juices with off-odors.

Molds can grow on the surface of improperly processed tomato products and may eventually reduce the acidity to a point where botulism-producing spores can grow and produce a deadly toxin. Because even minute amounts of botulism toxin can cause fatal illness, discard without tasting any canned products that show mold growth on the surface. Discard them where they cannot be eaten by other people or animals.

The processing times in this fact sheet are designed to ensure sufficient destruction of bacteria and molds. Where appropriate, processing recommendations for both water bath and pressure canning are given. In general, a pressure canner results in higher quality and more nutritious canned tomato products.

Yield Information

One bushel of fresh tomatoes weighs 53 pounds and yields approximately 18 quarts of canned tomatoes or 15 to 18 quarts of juice. Approximately 2 1/2 to 3 1/2 pounds of fresh tomatoes makes 1 quart of canned tomatoes.

Prepare Jars and Equipment

Standard mason jars are recommended for home canning. Be sure all jars and closures are perfect. Discard any with cracks, chips, dents or rust. Defects prevent airtight seals.

Wash jars in hot, soapy water and rinse well before using. Prepare metal lids as manufacturer directs.

Prepare Tomatoes

Select fresh, firm, ripe tomatoes. Do not can soft, overripe, moldy or decayed tomatoes or tomatoes harvested from dead or frost-killed vines. Green tomatoes are more acidic than ripened tomatoes and can be canned safely with any of the following recommendations.

Wash tomatoes well and drain. Dip in boiling water for 30 to 60 seconds or until the skins split. Then dip in cold water. Use a sharp knife to cut out the stem and all of the white core beneath the stem. Peel off the skin. Trim off any bruised or discolored portions.

Close Jars and Process

After jars are filled with food, remove trapped air bubbles, adjust the headspace, and clean the jar tops before processing. To remove trapped air bubbles, insert a nonmetallic spatula or knife between the food and the jar. Slowly turn the jar and move the spatula up and down to allow air bubbles to escape. Add more liquid if necessary to obtain the proper headspace (see recipes in Table 1). Wipe the jar rim with a clean, damp paper towel to remove any food particles. Place pretreated lid on the jar. Turn the screw band fingertip tight.

The jars are now ready to process in a boiling water bath or pressure canner.

After processing, carefully remove jars from canner and place on rack, dry towel or newspaper. Allow jars to cool untouched, away from drafts, for 12 to 24 hours before testing seals. To test jar seals, press flat metal lids at the center of lid. It should be slightly concave and not move. Remove screw bands. Label sealed jars with contents, canning method and date. Store in a clean, cool, dry, dark place.

Reprocessing

Jars of tomatoes or tomato products that do not seal can be safely reprocessed within 24 hours of the initial processing. However, if the jar sealed at first and then unsealed a few days later, spoilage is indicated. Do not reprocess such jars; destroy the contents.

To reprocess, remove lids and empty the food and liquid into a pan. Heat to boiling and pack into clean, hot jars. Put on new pretreated lids. Process again for the full time.

The quality of twice-processed foods may be lower, with textural changes and additional loss of heat-sensitive nutrients such as vitamin C and B-complex.

Table 1: Directions for Canning Tomatoes and Tomato Products in a Boiling Water Bath and/or Pressure Cooker

General Directions:  Wash, skin and trim tomatoes as described in the Prepare Tomatoes section. Fill jars according to the raw or hot pack method described for each product. Release air bubbles and close jars as described in the Close Jars and Process section. Process in a boiling water bath or pressure canner as directed for your altitude. Begin timing when water returns to boiling or when canner reaches correct pressure.