Tomatoes produce abundant crops in backyard gardens and tomato texture decreases significantly when frozen, so tomatoes are one of the most commonly canned foods. The acid level in tomatoes is usually below pH 4.6 so they are classified as an acid food for the purposes of home canning, however the pH of tomatoes may vary with the cultivar, growing conditions, and maturity so in the late 1980's the USDA changed tomato recipes to include an added acid and much longer processing times. These new procedures are a shock to people who have been canning tomatoes for decades, but currently they are the only safe recommendations we have.
This spoilage occurs in tomatoes and tomato juice fairly often. No gas is produced by these spoilage microorganisms so the lids remain flat on the jars and there is no noticeable change in appearance. The tomatoes will have a medicinal, sour, or bitter flavor. Sometimes there is also a sour odor. The bacteria that cause flat-sour spoilage are nonpathogenic (do not cause human illness), but such spoiled jars are unappetizing and should be discaarded.
The bacteria that cause this type of spoilage can exist in a very heat-resistant spore stage which is not killed by boiling water processing. Therefore, any boiling water processed jar of tomatoes could contain these live bacteria. The bacteria germinate and cause spoilage with warm storage temperature. Preventative measure is storing the canned food at cool temperatures but other steps also help. Hot packing, following the current USDA boiling water processing times, cooling the jars quickly after canning (cool completely on rack before packing away), and storing in a cool location decrease the change of flat-sour spoilage.
Return to Tomato MenuYour local County Cooperative Extension Office will have brochures with many safe, USDA tested recipes for canning tomatoes and tomato products. The following provides only recipes for the most common tomato canning. It is not a misprint, the USDA recommended processing times are really this long now.
Slip the tomato skins by dipping in boiling water then plunging in cold water. Core. Fill Jars with raw tomatoes, pressing until spaces fill with juice. Leave 1/2 inch headspace. Add 1 Tb lemon juice per pint and 2 Tb lemon juice per quart. May add salt (1 tsp/qt) for flavor if desired.
Adjust lids and process in a boiling water canner for 85 minutes at sea level, 90 minutes at 1001-3000 ft, 95 minutes at 3001-6000 ft, and 100 minutes at 6001-8000 ft. It is possible to shorten this processing time to 25 minutes if processed at 10 pounds in a pressure canner for pints or quarts at sea level.
Slip tomato skins by dipping in boiling water then plunging in cold water. Core and cut into quarters. Put a quart of tomatoes in a heavy saucepan and heat while crushing with a wooden spoon to press out juice. Add the rest of a canner load of tomatoes and continue to heat and stir. Bring to a boil and boil for 5 minutes. Fill jars with hot tomatoes leaving 1/2 inch headspace. Add 1 Tb bottled lemon juice per pint and 2 Tb bottled lemon juice per quart. If desired for flavor, add salt; 1 tsp/pint.
Process in a boiling water canner 34 minutes for pints and 45 minutes for quarts at sea level; or process in a pressure canner for 15 minutes at 10 pounds pressure at sea level.
Whole, Cold, Squished Tomatoes
Recipe adaped from 1991 Pacific NW Cooperative Extension Bulletin 300 and USDA tomato processing times.
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Crushed Hot Pack Tomatoes
Recipe from current USDA recommendations and Pacific NW Cooperative Extension Bulletin 300.
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