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How to Can Tomatoes

Canned Tomatoes

Just a few tomato plants will produce a crop of tomatoes too large to be consumed during the harvest season. To stretch garden gains and to prevent the waste of good produce the gardener will want to learn how to can tomatoes. The process of canning tomatoes in the form of juice, paste, whole, chopped, or diced tomatoes has been going on for more than a century. Home canning then is safe, if all of the rules regarding cleanliness, heat, and pressure requirements are strictly adhered to.1

To can tomatoes use the best fruit. Dispense with rotten, decaying, diseased, or very over-ripe tomatoes. For stewed tomatoes figure 10 pounds of tomatoes will make about three quarts. A bushel basket will make 17 to 20 quarts. Begin by preparing the area in which you intend to work. This means starting up a pressure canner, and having the jars ready. Sterilize the jars by placing them in boiling water for ten minutes. Do not try placing the jars in the oven at high temps as this can weaken the glass. Put pressure canner on stove, following the manufacturer's instructions - usually it is to place 2 to 3 inches of water in the bottom of the cooker.

Preparing Tomatoes for Canning

Set a pot on the stove big enough to accommodate a batch of tomatoes. To remove the skin from tomatoes, after washing, dip them, two or three at a time, in boiling water for 30 seconds to a minute, then place them in cold water. The skin should crack and be very easy to peel off with a knife. For quartered or diced tomatoes, cut them to preferred shape and place in pan on stove. Enough juice should be set free by this process to cover over the quarters. Set tomatoes to boil for about five minutes, adding any other desired ingredients such as basil or garlic. Up to one teaspoon of salt may also be added to enhance flavor and preservative qualities. Certainly add 2 tablespoons of lemon juice to every quart jar to ensure sufficient acid to inhibit bacterial growth. Fill sterilized jars from boiling pot to within 1/2 inch of the top.

Fit the jars with sterilized lids and, using a jar lifter, put them into the rack in a pressure canner.

Pressure Canner

Modern pressure canners generally have a screw-down lid, removable racks, a vent port with an automatic vent lock. They will come with a weight gauge or a dial gauge. The weight gauge jiggles to let off pressure at certain points, while the dial gauge builds or releases pressure based on the pressure on the dial. Be sure to read instructions on your own pressure canner to determine exact features. The pressure necessary for canning tomatoes is dependent on the altitude above sea level. For quartered or crushed tomatoes, the National Center for Food Preservation recommends that the following pressure should be used2:

  • Use a 5 pound weight gauge for 20 minutes at 1000 feet or less.
  • Use a 10 pound weight gauge for 20 minutes above 1000 feet.
  • Use a dial gauge at 6 pounds for 20 minutes 0 to 2000 feet.
  • Use a dial gauge at 7 pounds for 20 minutes 2000 to 4000 feet.
  • Use a dial gauge at 8 pounds for 20 minutes 4000 to 6000 feet.
  • Use a dial gauge at 9 pounds for 20 minutes 6000 to 8000 feet.

When the quart or pint jars have been placed into the canner and the temperature/pressure has reached prescribed level, let cook for twenty minutes. Remove the pressure cooker from heat and allow it to cool naturally. Once it has cooled, follow the manufacturer's directions for removing gauge and lid. (When removing lid, be sure to open with the lid away from the face to avoid steam burns.) Remove the jars from the pressure canner one at a time using the jar lifter. Set them aside on a towel and allow them to cool naturally to room temperature (12 to 24 hours). Do not tighten bands on lids until this process is complete. As the cans cool the tops should pop down ensuring a good seal. When the canned tomatoes have sufficiently cooled they can be placed in a cool, dry, and dark place.

Any tomatoes that do not seal properly can be placed in the refrigerator and used at the next convenient opportunity.

When opening tomatoes that have been canned, be sure that seal was unbroken during storage. When opening, there should be a sucking sound, and the lid should pop up. The smell of the tomatoes should be fresh. Do not eat tomatoes which smell bad or become discolored. Toxins can accumulate in canned goods that can be fatal.

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  1. Preserve Food on Canning Safety
  2. National Center for Food Preservation