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Canning tomato products - safety guidelines

Jars of home canned tomatoes.

Home canning tomatoes is a great way to preserve them for later use. Proper methods, choice ingredients and awareness of acidity levels are critical to a safe home-canned product.

Choose a newer recipe and follow directions

Directions and processing times for tomatoes and tomato products were re-evaluated for safety in the late 1980s. The updated directions were published in 1994 in the USDA Complete Guide to Home Canning. For safety sake, be sure to use a research tested recipe dated 1994 or newer. Be sure to select the recipe for the tomato product you are canning and follow all instructions exactly. 

The National Center for Home Food Preservation Canning Tomatoes and Tomato Products webpage lists over 15 options for home-canning tomatoes. Each recipe has specific directions on preparing the tomatoes, filling the jars and processing time.  

Choose only high-quality tomatoes

Choose fresh, vine-ripened tomatoes that are at their peak ripeness. Over-ripe tomatoes are less acidic. The acidity level in tomatoes varies throughout the growing season. Tomatoes reach their highest acidity when they are still green and decrease in acidity until they reach their lowest acidity as they mature.

Canning is NOT a way to use damaged tomatoes or those from dead or frost-killed vines. These tomatoes may have extra pathogens. The canning process time may not be enough to kill extra organisms. This could lead to a product that spoils and is unsafe to eat. 

Add acid to all tomatoes before processing

A high acid level (pH of 4.6 or less) prevents the growth of Clostridium botulinum bacteria which causes botulism. Because many factors impact the acidity level of tomatoes, USDA recommends adding acid to all home-canned tomatoes and tomato products.

Treat heirloom tomato varieties that same. The acidity of heirloom tomato plants is no different from the non-heirloom varieties. Some heirloom varieties are more low-acid than hybrid varieties. Therefore, the same acidification recommendations apply for canning heirloom tomatoes.

Factors that affect acidity level

Four red and green tomatoes growing on plant

Researchers have found that the acidity level of tomatoes can be affected by many factors, including:

  • The variety of tomato.
  • Stressful growing conditions.
  • Over-mature fruit.

Also, the acidity level of canned tomato products can be affected by:

  • Adding low-acid ingredients to tomatoes (such as onion and peppers).
  • Making juice versus tomato solids.
  • The canning process itself.

Forms of added acid

Added acid can be in the form of citric acid, lemon juice or vinegar.

Citric acid

Citric acid is available where canning supplies are sold or ordered online. Canning supply companies like Mrs. Wages® and Ball® have a powder form of citric acid. Some health food stores carry citric acid too; be sure it is food grade. 

Lemon juice

If using lemon juice, use commercially bottled juice. Don't use freshly squeezed lemon juice because the acidity level varies and there is a chance of contaminating the juice from the rind. You can safely use bottled lime juice instead of bottled lemon juice. 

Bottled lemon and lime juice contain sulfites. If you or family members have a sulfite sensitivity or allergy, use citric acid, vinegar or substitute frozen lemon juice (not lemonade) that you find in the grocery store frozen section; use same amounts as bottled lemon juice.

Vinegar

Will result in noticeable flavor change. You can add a small amount of sugar to help offset the flavor.

 

Add acid to all tomatoes when canning

Add acid directly to the jars before filling. Use the following chart for determining the amount of acid you will need.
Acid Effect Amount
Citric acid Little change in flavor 1/2 teaspoon per quart; 1/4 teaspoon per pint
Bottled lemon juice Easy to use 2 tablespoons per quart; 1 tablespoon per pint
Vinegar (5% acidity) Noticeable flavor change 4 tablespoons per quart; 2 tablespoons per pint

Note: Tomato canning tablets that may be found on the market should not be used because they are ineffective.

Pressure canner with jars and vegetables.

Process for the correct amount of time

Processing times are based on the type of liquid used to pack or fill the jar of tomatoes. Tomatoes with no added liquid or packed in tomato juice have longer processing times because the heat distribution is less effective in juice than in water.  Remember to adjust for Minnesota altitudes, choose processing times for 1001-2000 feet. Processing times found on this website are adjusted for Minnesota altitudes.

Minnesota home canning processing chart for tomatoes

This chart is provided for experienced canners familiar with safe canning methods. Time assumes a full 10 minute exhausting of the pressure canner. Once pressure is raised to an accurate level and stabilized, timing begins according to chart. For more complete canning instructions, refer to National Center for Home Food Preservation. * To ensure safe acidity in all canned tomato products, add bottled lemon juice or vinegar or citric acid directly to the jars before filling with product.
Type of food Style of pack Jar size Head space Boiling water bath Pressure canner Dial gauge Weighted gauge
Tomatoes* (no added liquid) Raw Pints and quarts ½ inch 90 minutes 25 minutes 11# 15#
Tomatoes* (packed in water) Hot and raw Pints ½ inch 45 minutes 10 minutes 11# 15#
Tomatoes* (packed in water) Hot and raw Quarts ½ inch 50 minutes 10 minutes 11# 15#
Tomatoes* (packed in juice) Hot and raw Pints and quarts ½ inch 90 minutes 25 minutes 11# 15#
Tomato Juice* Hot Pints ½ inch 40 minutes 15 minutes 11# 15#
Tomato Juice* Hot Quarts ½ inch 45 minutes 15 minutes 11# 15#
Cooking tomatoes.

Never add thickener before canning tomato products

Every year, home food preservers want to know how to thicken salsa or tomato soup with flour, cornstarch, rice, pasta or cream before canning. Never, under any circumstances, add a thickening product before canning. These thickening products will change the acidity level of your tomatoes. This also could create a thick product that does not allow good heat penetration. As a result, adding thickeners before canning may result in an unsafe product.

To produce a thicker tomato product:

  • Try using Italian plum-style or paste tomatoes vs. large slicing tomatoes.
  • Thicken salsas by adding tomato paste or by draining off some of the liquid after you chop the tomatoes.

Thicken just before serving

Thicken tomato products with flour, cream, cornstarch, etc. just before serving. If you do thicken your tomato soup mixture, it can be frozen successfully but never canned!

Suzanne Driessen, Extension educator; Carol Ann Burtness; and Deb Botzek-Linn, former Extension educator

Reviewed in 2018

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