Canning tomatoes: three methods
Tomatoes must be canned carefully to avoid spoilage and food poisoning. Some tomato varieties, even high-acid varieties, produce lower-acid fruits under some conditions. Therefore, always add bottled lemon juice or citric acid to avoid the risk of botulism.
Control spoilage by heat processing filled jars in a boiling water canner or a pressure canner. Researchers at Pennsylvania State University have recalculated processing times. They differ from recommendations prior to 1990.
Select only disease-free, vine-ripened firm tomatoes. Do not can overripe, damaged or frosted tomatoes, or ones from dead vines. They're lower in acid. Freeze them.
Pretreat new lids in a saucepan of simmering water, or follow manufacturer's instructions.
Three packing methods
Crushed tomatoes by hot pack method:
Peel, remove cores and quarter them.
Heat rapidly in a large kettle and simmer gently for 5 minutes. Crush with wooden spoon.
Add two tablespoons bottled lemon juice to each clean quart canning jar, then fill with hot tomatoes.
Add one teaspoon canning salt if desired.
Seal with two-piece canning lids; process quarts 50 minutes in a boiling water bath canner.
If you use a dial gauge pressure canner, process for 20 minutes at 6 pounds pressure, or 15 minutes at 11 pounds pressure.
With a weighted gauge canner, process 20 minutes at 10 pounds pressure, or 15 minutes at 15 pounds pressure.
Whole or halved raw tomatoes packed in water:
Add two tablespoons bottled lemon juice to each clean quart and fill with raw whole or halved tomatoes.
Cover tomatoes in jar with hot water, and wipe off jar lip with damp paper towel.
Adjust pretreated lids and screw ring onto jar.
Process quarts 50 minutes in a boiling water bath.
If you use a dial-gauge pressure canner, process for 15 minutes at 6 pounds pressure or 10 minutes at 11 pounds pressure.
With weighted gauge canner, process 15 minutes at 10 pounds pressure or 10 minutes at 15 pounds pressure.
Raw whole or halved tomatoes packed in juice:
(Tomatoes packed in juice need a much longer processing time to prevent spoilage.)
To each quart add two tablespoons lemon juice and one teaspoon salt.
Fill with peeled raw tomatoes.
Press to make enough juice to cover, or add previously strained hot juice.
Wipe off jar lip with damp paper towel.
Adjust pretreated lids and screw rings onto jars.
Process for 90 minutes in boiling water bath canner.
In a dial gauge canner, process 40 minutes at 6 pounds pressure, or 25 minutes at 11 pounds.
In a weighted gauge canner, process 40 minutes at 10 pounds pressure, or 25 minutes at 15 pounds pressure.
For more information on home food preservation, call 1-800-854-1678, hours: 9-12, 1-4 p.m. or www.umn.edu/distribution/nutrition