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Appetite for Knowledge

A Taste for Tomatoes

Do you enjoy the fresh taste of tomatoes just off the vine? Then take advantage of tomato season by learning how to preserve tomatoes the proper way!

I shudder when I think of how many people are innocently using unsafe tomato-canning techniques. As Extension educators, we are concerned about people using overripe or poor-quality fruit and old canning recipes because it could lead to botulism, which can be deadly. Botulism reveals no clues to its presence: no mold, no odor, no color, or taste change! It will grow and thrive in a perfectly sealed, but insufficiently heated, canning jar. Botulism can be prevented by following proper canning techniques and using the right equipment to avoid contamination.

Select only disease-free, preferably vine-ripened, firm tomatoes for canning. Do not can tomatoes from dead or frost-killed vines. Although tomatoes are generally considered a high-acid food, the fact is that their pH can vary greatly. Green tomatoes are more acidic than ripened fruit and can be safely canned. 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.

Procedure for whole or halved tomatoes packed in water: wash jars, prepare lids according to manufacturer’s instructions, and wash the tomatoes; then, with a sharp knife, make a shallow “X” on the bottom of each tomato. Heat a large pot of water to boiling. Dip the tomato in the boiling water for 30 to 60 seconds or until skins split. Immediately plunge the tomatoes into ice water to loosen the skins. Peel off the skin and remove the cores with a knife. Leave tomatoes whole or halve.

Add 1 tablespoon of bottled lemon juice or ¼ teaspoon of citric acid per pint of tomatoes. Per quart, add 2 tablespoons of bottled lemon juice or ½ teaspoon of citric acid.

The acidity levels for vinegars aren’t consistent. Always check on the bottle’s label for its acid percentage before using it. The USDA-approved recipes have been designed assuming a 5 percent acidity for the vinegar.

Be aware: if a salsa recipe requires bottled lemon juice, don’t make a substitution with vinegar. Lemon is more acidic, and the amount of low-acid vegetables in a particular salsa may need the additional acid that it provides. If a recipe calls for using vinegar, however, it can be replaced with lemon juice.

It is important not to change any ingredient proportions or canning instructions because USDA-approved tomato and salsa recipes have been tested for proper acidity using the prescribed measurements and methods.

You can be creative with the amounts of dried herbs and spices, but they are the only ingredients that are safe to alter in these recipes. Don’t be tempted to substitute fresh herbs for dried, which may throw off the precise balance of the other ingredients. If you want to use fresh herbs, add them before serving. If desired, add ½ teaspoon of salt per pint or 1 teaspoon of salt per quart.

For raw pack, heat a large pot of water to boiling. Fill hot jars with prepared raw tomatoes, leaving ½-inch headspace. Cover tomatoes in the jars with boiling water, leaving ½-inch headspace. Remove air bubbles and adjust the headspace if needed. These tomatoes will have a firmer texture, but will float to the top of the jars.

For hot pack products, put prepared tomatoes in a large saucepan and add enough water to completely cover them. Boil the tomatoes gently for 5 minutes. Fill hot jars with hot tomatoes leaving ½-inch headspace. Add the cooking liquid to the jars to cover the tomatoes, leaving ½-inch headspace. Remove air bubbles and adjust the headspace if needed. Since heated tomatoes are softer, more can fit into the jars, and there will be less floating.

Wipe the jar rims and threads with a clean, damp cloth. Add the hot lids and tighten each screw band to “finger-tight” resistance.

To process in a boiling water canner, fill a canner halfway with water and preheat it to 180°F for hot packs or 140°F for raw packs. Load the sealed jars onto the elevated canner rack with a jar lifter. Lower the rack down into the canner. Add hot water, if needed, to a level of 1-inch above jars and put the lid on the canner. When water boils vigorously, lower the heat to maintain a gentle boil and process jars according to a USDA-approved canning time. If you live in an altitude greater than 1,000 feet above sea level, you must make altitude adjustments. Call your local Extension office to find out how you need to make these adjustments.

When the processing time is complete, turn off the heat and remove the lid. Let the canner cool 5 minutes before removing the jars. Use the jar lifter to transfer the jars from the canner to a dry towel, placing them 1 to 2 inches apart to cool. Don’t tighten the bands or move jars for at least 12 hours. Then check the seal of each jar by pressing the center of the lid – it should not flex. If it does flex, the tomatoes should be frozen immediately or refrigerated and eaten within 10 days.

After checking the seals, remove the bands, and wipe the jars with a clean, damp cloth. Label and date the jars and store in a cool, dark place. For maximum quality and flavor, use the tomatoes within a year. As long as the seal of the jars remains intact, they can be stored up to 3 years; however, the quality will begin to decline, affecting color, flavor, and nutrition.

Before using canned tomatoes, always check for bulging lids or leaks. If either of these situations is present, throw the product out without tasting it. Once opened, spurting liquid, foam, mold, or an off odor are clear trouble signs, so immediately discard!

Your local Nutrition and Food Safety Extension educator will be able to help you. In addition, consult the U.S. Department of Agriculture’s Complete Guide to Home Canning – revised 2015 or a current Ball Blue Book or cookbook.

Capture the flavor of the ripest, juiciest tomatoes with these tips on preserving! I hope this will inspire you to create healthy dishes that come from the best place of all – your kitchen!

Written by Vicki Hayman, MS, University of Wyoming Extension Nutrition and Food Safety Educator


  • Ball Blue Book, USDA Complete Guide to Home Canning

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Home canned fresh tomatoes

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Extension Educators:
Shelley Balls – (307) 885-3132
Denise Smith – (307) 334-3534
Vicki Hayman – (307) 746-3531

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Issued in furtherance of extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kelly Crane, Director, University of Wyoming Extension, College of Agriculture and Natural Resources, University of Wyoming Extension, University of Wyoming, Laramie, Wyoming 82071.

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