Home Canning Tomatoes

Copyright ©  2000  Regents of the University of Minnesota. All rights reserved.

The USDA methods given in this publication are based on research released in 1988, sponsored by the United States Department of Agriculture, and conducted at the Extension Service Center for Excellence in Home Food Preservation, Pennsylvania State University.

Refer to Tomato Products (F0-3470) and Safe Home Canning Fruits, Vegetables, and Meats (BU-0516) for existing methods of products not found in this publication. Note: Processing times and pressures are for Minnesota altitude ranges. If you move to another state, be sure to check with the local cooperative extension office for the correct processing recommendations.

Tomatoes continue to be one of the most popular vegetables grown in the home garden. As a result, individuals often find themselves with an abundance of ripe tomatoes and want to preserve them for future use. Tomatoes are good sources of vitamins A and C. They also provide color and flavor associated with many mixed food items.

Tomatoes may be canned, frozen, or dried. However, canned tomatoes are generally more versatile for use by consumers. Since tomatoes must be preserved correctly to ensure safety, this publication presents researched methods of home canning.

Quality
Select only disease-free, preferably vine-ripened, firm fruit for canning. Caution: Do not can tomatoes from dead or frost-killed vines. These may result in an unsafe or low acidity. Green tomatoes are more acidic than ripened fruit and can be canned safely with any of the following recommendations.

Acidity of Foods
The acidity of substances is generally expressed in terms of pH. The pH scale ranges from 1 to 14, with 1 the most acidic, 14 the most alkaline, and 7 being neutral. Most foods have a pH below 7 (see Table 1).

High acid foods are those with a pH below 4.6. These include fruits, properly made pickles and sauerkraut, jams, jellies, and fruit butters. These foods are safely canned in a boiling water bath because the acidity is great enough to prevent the spores of Clostridium botulinum, which is naturally present on most fruits and vegetables that come in contact with soil, from germinating, growing, and producing a deadly toxin. This bacteria requires no or very low oxygen levels to grow. Canned foods are of particular concern because air is driven out with heat and prevented from reentering by sealing the jar. This may provide ideal conditions for growth and toxin production if proper acidity is not present or researched canning methods are not followed.

Low acid foods are those with a pH above 4.6. These include meat, seafood, poultry, figs, and most vegetables. Low acid foods do not contain enough acid naturally to prevent the germination and growth of the botulinum spores. Thus, these foods must be processed in a pressure canner that reaches high temperatures (above 240 degrees F) long enough to kill the spores and still retain good nutritive value and overall quality.

Table 1. Tomatoes generally have high acidity and a low pH. However, some varieties are close to having a low acidity. To be certain of proper acidity (pH below 4.6), USDA recommends the addition of acid.

Tomato Acidity
Tomatoes are generally considered a high acid food item with a pH below 4.6. Unfortunately, a lot of misinformation has been printed in the popular press about "low acid" tomatoes referring to those with a sweet, non-tart taste. These tomatoes are often white, yellow, or pink in color but are not low in acid content. The higher sugar masks the acidic flavor.

Researchers at USDA and at the University of Minnesota have found that most underripe to ripe, cooked tomatoes have a pH below 4.6. Unfortunately, a few varieties may have a pH above or close to 4.6. These include Ace, Ace 55VF, Beefmaster Hybrid, Big Early Hybrid, Big Girl, Big Set, Burpee VF Hybrid, Cal Ace, Delicious, Fireball, Garden State, Royal Chico, and San Marzano. Some of these are grown for commercial purposes and are not found in home gardens. However, safely canning these varieties requires additional acid for water bath processing or a pressure canning process similar to low acid vegetables.

Method Choices
The new USDA Home Canning Guides recommend the addition of lemon juice or citric acid to each jar of every tomato product to be certain of correct pH. This procedure is recommended for those individuals who are using one of the varieties listed previously, who are using unknown varieties, or who wish to further minimize any potential botulism risk. These methods are listed under USDA Methods in this publication. Also considered in these methods are higher solid tomatoes that yield less water when cooked. Thus, added water or a longer heat process is recommended to ensure adequate heat penetration.

Boiling water bath and pressure canning processes are given. However, USDA recommends using a pressure canner which may result in a higher quality and more nutritious product.

Those methods listed under Minnesota Methods in this publication were previously researched at the University of Minnesota and are widely accepted for use with normal high acid tomatoes at Minnesota altitudes. It is important to be certain that the tomatoes used following these methods are underripe to ripe and not soft, overripe, decayed, one of the listed high pH varieties, or those of uncertain acid content.

Acidification
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, use 1 tablespoon bottled lemon juice or 1/4 teaspoon citric acid. Acid can be added directly to the jars before filling with the 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. However, vinegar may cause undesirable flavor changes.

TOMATO JUICE

Quantity
An average of 23 pounds is needed per canner load of 7 quarts, or an average of 14 pounds per canner load of 9 pints. A bushel weighs 53 pounds and yields 15 to 18 quarts of juice-an average of 3-1/4 pounds per quart.

Procedure
Wash, remove stems, and trim off bruised or discolored portions. To prevent juice from separating, quickly cut about 1 pound of fruit into quarters and put directly into saucepan.

Heat immediately to boiling while crushing. Continue to slowly add and crush freshly cut tomato quarters to the boiling mixture. Make sure the mixture boils constantly and vigorously while you add the remaining tomatoes. Simmer 5 minutes after you add all the pieces.

If you are not concerned about juice separation, simply slice or quarter tomatoes into a large saucepan. Crush, heat, and simmer for 5 minutes before juicing.

Press both types of heated juice through a sieve or food mill to remove skins and seeds. Add bottled lemon juice or citric acid to jars. See instructions under Acidification. Heat juice again to boiling. Add 1 teaspoon of salt per quart to the jars, if desired. Fill jars with hot tomato juice, leaving a 1/2-inch headspace. Adjust lids and process.

1. Boiling Water Bath:
   • Pints, 40 minutes
   • Quarts, 45 minutes
2. Dial-gauge Pressure Canner:
   • Pints and Quarts,
   • 20 minutes 6 PSI or
   • 15 minutes 11 PSI
3. Weighted-gauge Pressure Canner:
   • Pints and Quarts,
   • 20 minutes 10 PSI or
   • 15 minutes 15 PSI

CRUSHED TOMATOES
WITHOUT ADDED LIQUID

A high-quality product, ideally suited for use in soups, stews, and casseroles.

Quantity
An average of 22 pounds is needed per canner load of 7 quarts; an average of 14 fresh pounds is needed per canner load of 9 pints. A bushel weighs 53 pounds and yields 17 to 20 quarts of crushed tomatoes-an average of 2-3/4 pounds per quart.

Procedure
Wash tomatoes and dip in boiling water for 30 to 60 seconds or until skins split. Then dip in cold water, slip off skins, and remove cores. Trim off any bruised or discolored portions and quarter. Heat 1/6 of the quarters quickly in a large pot, crushing them with a wooden mallet or spoon as they are added to the pot. This will exude juice. Continue heating the tomatoes, stirring to prevent burning. Once the tomatoes are boiling, gradually add remaining quartered tomatoes, stirring constantly. These remaining tomatoes do not need to be crushed. They will soften with heating and stirring. Continue until all tomatoes are added. Then boil gently 5 minutes. Add bottled lemon juice or citric acid to jars. See instructions under Acidification. Add 1 teaspoon of salt per quart to the jars, if desired. Fill jars immediately with hot tomatoes, leaving a 1/2-inch headspace. Adjust lids and process.

1. Boiling Water Bath:
   • Pints, 40 minutes
   • Quarts, 50 minutes
2. Dial-gauge Pressure Canner:
   • Pints and Quarts,
   • 20 minutes 6 PSI or
   • 15 minutes 11 PSI
3. Weighted-gauge Pressure Canner:
   • Pints and Quarts,
   • 20 minutes 10 PSI or
   • 15 minutes 15 PSI

WHOLE OR HALVED TOMATOES
PACKED IN WATER

Quantity
An average of 21 pounds is needed per canner load of 7 quarts; an average of 13 pounds is needed per canner load of 9 pints. A bushel weighs 53 pounds and yields 15 to 21 quarts-an average of 3 pounds per quart.

Procedure (for hot or raw tomatoes filled with water in jars)
Wash tomatoes. Dip in boiling water for 30 to 60 seconds or until skins split; then dip in cold water. Slip off skins and remove cores. Leave whole or halve the tomatoes. Add bottled lemon juice or citric acid to jars. See instructions under Acidification. Add 1 teaspoon of salt per quart to the jars, if desired. For hot-pack products, add enough water to cover the tomatoes and boil them gently for 5 minutes. Fill jars with hot tomatoes or with raw peeled tomatoes. Add the hot cooking liquid to the hot pack, or hot water for raw pack, to cover the tomatoes, leaving a 1/2-inch headspace. Adjust lids and process.

1. Boiling Water Bath:
   • Pints, 45 minutes
   • Quarts, 50 minutes
2. Dial-gauge Pressure Canner:
   • Pints and Quarts,
   • 15 minutes 6 PSI or
   • 10 minutes 11 PSI
3. Weighted-gauge Pressure Canner:
   • Pints and Quarts,
   • 15 minutes 10 PSI or
   • 10 minutes 15 PSI

WHOLE OR HALVED TOMATOES
PACKED IN TOMATO JUICE

Quantity
See the method for "Whole or Halved Tomatoes Packed in Water" listed previously.

Procedure
Wash tomatoes. Dip in boiling water for 30 to 60 seconds or until skins split, then dip in cold water. Slip off skins and remove cores. Leave whole or halve the tomatoes. Add bottled lemon juice or citric acid to the jars. See instructions under Acidification. Add I teaspoon of salt per quart to the jars, if desired.
Raw pack: Heat tomato juice in a saucepan. Fill jars with raw tomatoes, leaving a 1/2-inch headspace. Cover tomatoes in the jars with hot tomato juice, leaving a 1/2-inch headspace.
Hot pack: Put tomatoes in a large saucepan and add enough tomato juice to completely cover them. Boil tomatoes and juice gently for 5 minutes. Fill jars with hot tomatoes, leaving a 1/2-inch headspace. Add hot tomato juice to the jars to cover the tomatoes, leaving a 1/2-inch headspace. Adjust lids and process.

1. Boiling Water Bath:
   • Pints and Quarts, 90 minutes
2. Dial-gauge Pressure Canner:
   • Pints and Quarts,
   • 40 minutes 6 PSI or
   • 25 minutes 11 PSI
3. Weighted-gauge Pressure Canner:
   • Pints and Quarts,
   • 40 minutes 10 PSI or
   • 25 minutes 15 PSI

WHOLE OR HALVED TOMATOES
PACKED RAW WITHOUT ADDED LIQUID

Quantity
See the method for "Whole or Halved Tomatoes Packed in Water" listed previously.

Procedure
Wash tomatoes. Dip in boiling water for 30 to 60 seconds or until skins split, then dip in cold water. Slip off skins and remove cores. Leave whole or halve the tomatoes. Add bottled lemon juice or citric acid to the jars. See instructions under Acidification. Add 1 teaspoon of salt per quart to the jars, if desired.

Fill jars with raw tomatoes, leaving a 1/2-inch head-space. Press tomatoes in the jars until spaces between them fill with juice. Leave a 1/2-inch headspace. Adjust lids and process.

1. Boiling Water Bath:
   • Pints and Quarts, 90 minutes
2. Dial-gauge Pressure Canner:
   • Pints and Quarts,
   • 40 minutes 6 PSI or
   • 25 minutes 11 PSI
3. Weighted-gauge Pressure Canner:
   • Pints and Quarts,
   • 40 minutes 10 PSI or
   • 25 minutes 15 PSI

It is important to be certain that the tomatoes used following these methods are underripe to ripe and not soft, overripe, decayed, one of the listed high pH varieties, or those of uncertain acid content.

Tomatoes that produce insufficient juice to fill the jar should be prepared and processed using the USDA method, "Whole or Halved Tomatoes, Packed Raw Without Added Liquid."

WHOLE OR QUARTERED TOMATOES
PACKED RAW USING A WATER BATH PROCESS

Wash tomatoes and dip into boiling water for 30 seconds. Plunge into cold water. Drain, peel, and core. Put room temperature or warmer whole tomatoes (or cut tomato quarters) into clean jars. Press down with a spoon to pack. The juice will fill the jar. Do not add any water. Remove air pockets by sliding a rubber spatula down the side of the jar.

If desired, add 1 teaspoon salt to each quart and 1/2 teaspoon to each pint. This is optional and does not affect preservation. Leave a 1/2-inch headspace.

Wipe rim of jar with clean cloth. Apply two-piece canning lid following manufacturer's instructions. Process after adjusting lids.

• Recommended Process
• Boiling Water Bath:
  • Pints, 40 minutes,
  • Quarts, 50 minutes

Note: Processing time may be reduced 5 minutes for each size container by hot packing. Follow this basic procedure, but bring tomatoes to a boil, then quickly pack into jars leaving a 1/2-inch headspace. Adjust lids and process. Do not reduce processing time if processing below 1,000 feet.

WHOLE OR QUARTERED TOMATOES
PACKED RAW USING A PRESSURE PROCESS

Pack the tomatoes as described in "Whole or Quartered Tomatoes Packed Raw Using a Water Bath Process."

Place the tomato jars in a pressure canner containing 2 to 3 inches of boiling water.

Lock the lid into a closed position. Put the burner on high. After a steady column of steam has been escaping from the vent for approximately 10 minutes, put on the pressure regulator or weighted gauge. When the dial gauge or weighted gauge indicates the pressure has stabilized at 15 pounds (2 minutes minimum), turn off the heat and allow the pressure to return to 0 pounds. If an electric range is being used, remove the canner from the burner.

Remove pressure regulator or weighted gauge. After 10 minutes, unlock the lid and remove the canner cover.

TOMATO MIXTURE

• 12 cups tomatoes
• 1 cup chopped celery
• 1/2 cup chopped onion
• 1/2 cup chopped pepper
• 3 tsp. salt

This mixture of ingredients achieves the necessary acidity for water bath processing. Do not use the varieties of tomatoes listed previously with pH values near or above 4.6. Do not add any more pepper, onion, or celery than indicated. This will reduce the acidity of the mixture.

Quantity
The amount of ingredients listed yield 7 pints (for 7 quarts, double the ingredient amounts).

Procedure
Simmer the vegetables for 10 minutes. Pack into clean, hot canning jars. Leave a 1/2-inch headspace. Apply two-piece canning lids following the manufacturer's instructions. Process using the methods and times given for Minnesota Methods, "Whole or Halved Tomatoes Packed Raw Using a Water Bath or a Pressure Process."

FOR ALL METHODS

Remove hot jars from canner with lifter. Cool jars up-right on a clean and dry cloth, wooden board, or rack.

Check for seal failure after 12 to 24 hours. Store sealed jars in a cool dry place at 70 F or below.

For added safety, boil products 10-15 minutes before serving. The heat will destroy any botulism-causing toxins that may still exist despite the precautions taken.

Reminders When Using a Boiling Water Bath Process

1. Be certain water covers jars 1 to 2 inches over top.
2. Check for free circulation of water around each jar.
3. Keep water boiling during the entire processing time.
4. Keep a cover on the container.
5. Add more boiling water if water level lowers due to evaporation.
6. Start counting the processing time when the water returns to a good rolling boil after the jars are added.
7. Do not shorten the processing time.

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

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