Note: This canning whole tomatoes guide uses easy water-bath canning. You can certainly use a “canner” if you have one. OR, you can use a large deep stockpot with a flat bottom and lid. 

Making canned tomatoes is a tradition that families remember years later—and can even pass down to the next generation. Save a couple days in August or when tomatoes are at their peak and enjoy preserving summer in a jar!

If you are growing your own tomatoes, it’s important that you pick the tomatoes when ripe (not overripe). But if you are buying tomatoes, purchase tomatoes a few days in advance of processing day and allow to ripen at room temperature. Farmers really don’t have the luxury of waiting until tomatoes are at peak ripeness, as the fruit becomes too easy to bruise at this stage, and tomatoes continue to ripen in the box or on the counter with the potential to spoil.

Harvest when the tomatoes are ripe and no more. The USDA recommends avoiding using tomatoes picked from dead or frost-killed plants.

Safety First!

Canning, while requiring knowledge, is not that difficult. However, we must add a safety precaution: Canning must be done right.
Improper canning techniques can lead to the growth of the bacteria, Clostridium botulinum, that produces a toxin (botulin) that causes botulism, which is deadly illness. To prevent this bacterium from growing and releasing botulin in your canned goods, you need to lower the pH of your canning mixture - in other words, the canning mixture must be made acidic using lemon juice, citric acid or vinegar.

High-Acid vs. Low-Acid Tomatoes

In the past, tomatoes were considered a high-acid food which meant that they could be canned without the addition of an acid. However, we now understand that the acidity of a tomato depends on its variety and its ripeness, which makes it impossible to know for sure, if it is high- or low-acid. Therefore, tomatoes should always be treated as a low-acid food when it comes to water bath canning, and an acid must be added to each jar of tomatoes and tomato products for safety’s sake. 

How to Can Tomatoes: Crushed Tomatoes Recipe

This recipe is for “crushed tomatoes,” which resemble halved tomatoes in flavor and texture. They’re ideal for sauce, soup, and stew recipes.

While you may be tempted to add other ingredients, it’s best to stick to this recipe until you really know how to can, as it has been tested for safety, and it is a good introduction to canning at home. 

How Many Tomatoes Do I Need?
To make 1 quart of crushed tomatoes, you’ll need about 3 lbs. of tomatoes (for 1 pint, about 1.5 lbs.). If possible, use a scale to measure out exact amounts. Or, if you don’t have one handy, know that three baseball-sized tomatoes or eight plum tomatoes equal about 1 pound. A typical water-bath canner holds seven-quart jars or nine-pint jars at a time.

Ingredients

• 3 lbs. tomatoes per quart jar (1.5 lbs. tomatoes per pint jar) Tomatoes should be free of crack, spots, and growths
• Salt (optional)
• Bottled (not fresh) lemon juice or powdered citric acid

Supplies

• Pot with boiling water; pan of cold water
• Pot for cooking tomatoes
• Slotted spoon
• Wooden spoon or mallet
•  Paring knife and cutting board
• Water-bath canner (OR a large deep stockpot with a flat bottom, a well-fitting lid and a rack that fits at the bottom)
• Quart- or pint-sized canning jars and lids (as many as needed), screw bands, cloth to wipe the jars, jar lifter (jar tongs)
• Funnel and ladle 
• Marker for labeling jars

1. Preparing the Tomato Mixture

Set a pot of water to boil and thoroughly wash the tomatoes, removing any minor blemishes and form an X on the bottom with a paring knife. Then, using a slotted spoon, dip the tomatoes (maybe three or four at a time) into the boiling water and leave until the skins slip off about 30 seconds.

Removing the tomatoes with the slotted spoon, they immediately go into a pan of cold water to cool down and then place on a clean plate while the rest of the tomatoes are processed.

Once all the skins are loose, I pull off the skin, cut out the stem and tough part of the core. Placing the tomato on a cutting board, cut into small pieces.

Then place approximately one-sixth of the tomato pieces into a large pot and crush them with a wooden spoon or mallet to liquefy them. Place the pot on a burner, setting it to medium-high heat. Heat and stir the tomatoes until they come to a boil, then add the remaining tomato pieces, gradually. These pieces don’t need to be crushed, as they will be softened by the heat and stirring. Once all the tomatoes are added, allow the tomatoes to boil gently for 5 minutes.

2. Canning the Tomato Mixture

Wash the canning jars, bands and set-aside, and using your dishwasher makes this task easier.  

Jars get used year after year, but lids can only be safely used once. The lids on the market today do not need to be heat-activated before using. Just make sure they are clean. Fill a water bath canner about ½ to ¾ full of water and set the canner on the stove to boil.

Next, line up the jars and add the acid to each jar. Use these measures exactly:

• 2 tbsp lemon juice or ½ tsp. citric acid in quart jars;
• 1 tbsp lemon juice or ¼ tsp. citric acid in pint jars. 

It’s best to add the acid to the jars before adding the tomato mixture so that 1) you know for sure that you’ve added it, and 2) you don’t accidentally forget to leave room for them at the end!

• Also, add 1 teaspoon salt in the quarts or ½ teaspoon of salt in the pints for flavor, if you wish.

Once the water is boiling in your canner, you are ready to continue. With the jars lined up on the counter and the acid added, I ladle the hot tomato mixture into each jar, using a funnel to prevent spilling. Be sure to leave ½ inch of head space in each jar.

Next comes a VERY IMPORTANT step—it’s absolutely critical to wipe off the top of the jar with a cloth before putting on the lid. Any tiny particle of food left on the rim could cause a jar to not properly seal. Pop on the lid, adjust the screw band until finger tight, and prepare for processing.

3. Processing the Jars

Once the jars all have the lids and screw bands on, carefully place them in the water bath canner using the jar lifter.

Make sure that everything continues simmering while you are filling the canner and that there is at least 1 to 2 inches of boiling water above the top of the jars. Put the cover on the pot, bring to a boil and start timing the processing.

Source: National Center for Home Food Preservation

Note: Processing takes longer at higher altitudes, so consult this table to see how much time is required in your area. A small battery timer is handy for this. After cleaning up the accrued dishes, I take a break and read while my jars are dancing away.

Being mindful of the steam, check on your jars about halfway through the processing time to ensure that they are still submerged, boiling and with at least 1 inch of boiling water covering them. Add more boiling water, if needed.

Once the timer dings, I turn off the stove and very carefully take the top off of the pot venting the steam away from me. With a nice wooden trivet or a cloth towel on the table or counter nearby, I slowly take out each jar using the jar lifter and place each jar apart to cool. Be sure that the jars are not located in a draft, as a cold breeze can crack the jars at this point. This is also why I move them slowly.

Once all of this has been accomplished, I generally call it a day. There will be a noticeable (and reassuring) “pop” as the individual jars cool and seal. I look lovingly at my beautiful trivet of summertime bounty, and I wait until the next day to finish the job.

The jars are cool by morning (or within 12 to 24 hours). I take off the screw bands (carefully) because they sometimes get food on them and leaving them on makes them rust. I test each lid by gently pressing down. Any that give or flex did not seal correctly. Refrigerate any that did not seal immediately.  

Cooled jars for my “beauty shot.” Note: Make sure jars are cool. The ceramic trivet could cause the jars to crack!

The screw bands get washed and put aside for next year. I label each and every lid this way you won’t have to scrub any labels off of the jar because the lid gets tossed anyway with the year and the contents. Into the pantry go the canned tomatoes to await use in canned tomato soup, stews, American chop suey (I cook the elbows right in the mix) or anything else I decide to make during the long winter months. Yum!

Learn More

• If you need more advice on how to can your vegetables, or are looking to can more than just tomatoes, see our Water-Bath Canning Guide and Pressure Canning Guide.
• For more information, see the National Center for Home Preservation.
• If you feel that you’d rather dry your tomatoes than can them, learn how here. Whatever you choose, good luck making the most of your tomato harvest!

This Canning Guide was updated and fact-checked as of August 2020, by Christina Ferroli, PhD, RDN, FAND.  If interested in nutrition counseling and education practice to make healthier choices—or, simply stay up-to-date on the latest food, nutrition, and health topics—visit Christina’s Facebook page here.