Tomatoes are processed by using either a pressure canner or a water-bath canner. Prepare your canning jars by checking them over to make sure there are no dangerous visible cracks or uneven edges that might hinder the secure sealing of the tomatoes. Be sure that the rubber bands fit appropriately. Wash and dry both the jars and the bands thoroughly in hot, sudsy water; rinse completely, and air dry.
Heat jars and lids in simmering water at 180 degrees, making sure that you do not over-boil the lids. Let them stand in the hot water until they are ready to be filled.
If using a water canner, fill halfway with water. Place in wire canner rack, and bring water to a low, wavy heat of 180 degrees.
Choose firm, spot-free tomatoes, and wash them before placing in a wire basket. Gently lower the basket into the boiling water, blanching them just until the skins begin to crack. Take tomatoes out and plunge them directly into a pan of cold water.
Gently peel off the skins of the tomatoes, cut out the cores, and get rid of any green sections. At this time, you can choose to slice the tomatoes into any size pieces you want or even leave them whole.
Lightly insert the tomatoes into a hot jar, leaving a half-inch breathing space. This will allow you to be able to spoon the cooking liquid itself into the jar, creating juice for your tomatoes. Using a rubber or wooden spatula, press tenderly on the tomatoes to be sure there are no air bubbles trapped inside. Put a band and a hot lid onto the jar, and make sure that it is sealed securely.
Load the water canister rack with filled jars, then lower it into the 180-degree water and make sure that the water rests above the jars by 2 inches. Place the lid of the canner on. Once the water comes to a rolling boil, the tomato processing begins. Pints take approximately 40 minutes, while quarts take 45 minutes. When the process is complete, take off the lid, allowing tomatoes to sit and cool before removing. Upon taking the jars out, place them 2 inches apart on a dry towel and permit the tomatoes to rest at least 24 hours. You may then label and store them in a dry, dark spot.
A couple of additional notes: It is best to choose firm, vine-ripe tomatoes when canning. For a guaranteed safe amount of acidity, consider adding a couple of tablespoons of lemon juice or half a teaspoon of citric acid per quart jar.
Tomato Canning Basics