Canning Tomatoes. It's EASY! Tomatoes 1/4 teaspoon Citric acid (or 1/4 teaspoon Lemon Juice) Salt Jars/Lids Boil tomatoes in hot water until skins start to loosen. Remove and put in cold water with ice to cool. Once cool, remove skin and core tomatoes. Place tomatoes in sterilized jars. Fill leaving 1/2 inch space at the top. Sprinkle in citric acid (1/4 teaspoon per jar) and a dash of salt. Wipe off rim of jar and top with lid. Hand tighten. Place in hot bath (boiling water) for 85 minutes. Wat