How do I can Tomatoes?

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  • Written By: Karyn Maier
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  • Last Modified Date: 23 February 2020
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The tomato is one of the most popular garden perennials grown in the U.S. Aside from being delicious to eat, tomatoes are packed with nutrition. For instance, tomatoes contain vitamin C and lycopene, two potent antioxidants. Although tomatoes are usually a summertime crop, many gardeners and cooks look forward to canning them to enjoy year-round.

Learning how to can tomatoes isn’t difficult, but it does require a basic understanding of the canning process. First, the purpose of canning tomatoes is to reduce the risk of bacterial contamination. In their natural state, tomatoes have a very high water content, which can promote the growth of bacteria, yeast and molds. However, by using proper canning techniques, tomatoes can be preserved by forming a vacuum seal to protect the food from air and microorganisms.

For optimal color and flavor, the best time to can tomatoes is within 12 hours of harvesting them from the garden. It’s also important to choose disease-free tomatoes, although small irregularities may be trimmed off with a paring knife. You’ll get the best texture and quality if you pick tomatoes that are firm and that have been allowed to ripen on the vine. Of course, before you can tomatoes, you’ll want to wash them gently in cool running water to remove any surface dirt or debris.


Before you begin to can tomatoes, other preparations must be made. For example, acidification is required, whether using whole or crushed tomatoes. Generally, for every quart (0.95 liters) of tomato product to be canned, you should add two tablespoons (29.57 milliliters) of lemon juice. This will ensure the proper pH of the product and prevent bacterial growth. The lemon juice may be added to the canning jars before filling with tomato product.

You will also need to remove the skins before you start to can tomatoes. To do this, dip each tomato in boiling water for a few moments. Once the skin splits, remove the tomato and quickly dip it in cold water. This will allow the skin to easily slip off. You may then cut each tomato in half, or simply leave them whole. Many people decide to can tomatoes whole since they can easily be sliced or crushed after opening.

Next, the tomatoes are placed in a large saucepan or Dutch oven. Add enough tomato juice to the pan to just cover the tomatoes and bring to a boil. After five minutes, quickly fill your canning jars with the tomato product, leaving one-half inch (12.7 millimeters) of space at the top. Using gloves or oven mitts, place the jars into a canning bath (boiling water canner) and cover each with a lid. Note that the screw rings are added during the cooling, if used at all.

Process the jars in the water bath for 80-90 minutes. After processing, the jars are removed from the water bath and allowed to cool on a protected surface. Most boiling water canners come equipped with a lift-out rack to make this task easier. During the cool down phase, you may hear a series of ‘pops,’ which indicates that the jars have formed a vacuum seal. Once sealed, you may add the screw rings to the jars, if you wish.

Whenever you can tomatoes, you must remember to inspect each jar individually to make sure they have sealed properly. You’ll be able to tell by running your fingers across the top of the lid. If it is smooth, it has sealed; if there is still a bump remaining on the lid, it has not. In the event of the latter, the product must be either used right away, or reprocessed.


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