To can stewed tomatoes in a water bath, take the skins off firm tomatoes, boil them in water, and fill the canning jars with the stewed tomatoes. Put the filled canning jars with their lids on into a bath of hot boiling water, and ensure the canning jars are covered by 1 to 2 inches of water. Boil the jars for 35 to 45 minutes depending on their size.
Some other tips for canning stewed tomatoes are to remove tomato skins by dipping the tomato in boiling water for about 30 seconds and then cover them in cold water. The skins can be removed easily after this.
Also, after the tomatoes are stewed, add 1/2 teaspoon of citric acid or 2 tablespoons of lemon juice per quart if the tomatoes are too ripe or bruised. Make sure the tomatoes are hot when they are packed into the can. Boil the canned tomatoes for 35 minutes for pint-sized cans and 45 minutes for quart-sized cans.
Canning guides prior to 1983 provide different instructions that can result in unsafe canning. Botulism from canned tomatoes is rare, but the recommendations set by the USDA in 1985 advise home canners to stay away from cold packing tomatoes.