Special Hints on Canning Tomatoes
Recent research shows four tested cultivars (varieties) are not suitable for home canning because of their low acidity. These cultivars are Ace, Ace 55VF, Cal Ace, and Garden State.
Other factors that are of far more importance to the safety of home-canned tomatoes include:
- Ripeness of tomatoes — Use only firm, ripe tomatoes. Overripe tomatoes may be low enough in acid to support Clostridium Botulinum.
- Tomatoes on dead vines — Tomatoes harvested and canned after the vines are dead are low in acid.
- Infected tomatoes — Use tomatoes that are free from spoiled parts or mold, as infected tomatoes may be low in acid and could cause spoilage.
- Method and time of processing — "Open kettle" method is unsafe because undesirable organisms will grow and could lower the acidity. Also, if spores of Clostridium botulinum are present, they will not be destroyed. Use the times in the boiling water bath canner suggested in this section of the cookbook. If tomatoes are not processed long enough, organisms will continue to grow and change acidity and could produce botulism toxin.
- Ingredients in canned tomato products — Do not attempt to add any ingredients to the tomatoes other than those given in the directions. They might lower the acidity.
If you have any doubt about the tomato varieties you're canning, add bottled lemon juice or U.S.P. citric acid before processing to increase the acidity. USDA tests show the following levels are acceptable for taste and safety.
- Bottled lemon juice — Fill or pack jars to 3/4 inch of the top. Add 1 /2 teaspoon salt to each pint and 1 teaspoon to each quart. Then add 1 tablespoon lemon juice to each pint or 2 tablespoons to each quart. Adjust lids and process in boiling water bath or steam pressure canner as outlined for Hot Pack or Raw Pack for tomatoes, or Hot Pack for tomato juice.
- U.S.P. citric acid — Fill or pack jars to 1/2 inch of the top. Add 1/4 teaspoon U.S.P. citric acid to each pint and 112 teaspoon to each quart. Adjust lids and process in boiling water bath or steam pressure canner as outlined for Hot Pack or Raw Pack for tomatoes, or Hot Pack for tomato juice.
So much vinegar would have to be added to acidity tomatoes that the taste would not be acceptable.