By canning tomatoes, you can enjoy that garden-fresh tomato taste in sauces, soups, and stews all year long! Here’s how to can tomatoes using water-bath canning, step-by-step.
If you are growing your own tomatoes, it’s important that the tomatoes are ripe. But if you are buying tomatoes, purchase canning tomatoes a few days in advance of the processing. Farmers really don’t have the luxury of waiting until tomatoes are super-ripe, as the fruit becomes too easy to bruise at this stage. However, tomatoes will continue to ripen in the box or on the counter.
Harvest when the tomatoes are ripe and no longer. The USDA recommends avoiding using tomatoes picked from dead or frost-killed plants.
A Word of Warning: Safety First!
Canning is not that difficult, but we must add a safety precaution: Canning must be done right.
Improper canning techniques can lead to the growth of a bacteria that causes botulism, which is a potentially deadly illness. To prevent this bacteria from growing in your canned goods, you need to lower the pH of your canning mixture (in other words, the canning mixture must be made acidic).
**To prevent this bacteria from developing in your canned goods, you MUST add an acid—either bottled lemon juice or powdered citric acid—to EVERY canned food that you process.**
The USDA recommends adding 2 tbsp bottled lemon juice or ½ tsp. powdered citric acid to each quart jar of tomatoes (for pints, 1 tbsp lemon juice or ¼ tsp. citric acid).
Again, acid must be added to every jar that you process, regardless of whether the food you are canning is considered “high-acid” or “low-acid,” or whether you’re using the pressure-canning or water-bath canning method.
High-Acid vs. Low-Acid Tomatoes
In the past, tomatoes were considered a high-acid food, which suggested that they could be canned without any supplemental 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 canning, and supplemental acid must be added 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.
This recipe comes from the USDA’s Complete Guide to Home Canning. 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 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 & Supplies
3 lbs. tomatoes per quart jar (1.5 lbs. tomatoes per pint jar)
Bottled (not fresh) lemon juice or powdered citric acid
Pot with boiling water; pan of cold water
Pot for cooking tomatoes
Wooden spoon or mallet
Knife and cutting board
Water bath canner
Quart- or pint-sized canning jars and lids (as many as needed), screw band, cloth to wipe the jars, jar tongs
Funnel and ladle
Marker for labeling jars
Preparing the Tomato Mixture
Set a pot of water to boil and thoroughly wash the tomatoes, removing blemishes. Then, using a slotted spoon, dip the tomatoes (maybe three or four at a time) into the boiling water until the skins slip off (about 30 seconds). Removing them with the spoon, they immediately go into a pan of cold water to cool down and are then placed on a clean plate while the rest of the tomatoes are processed. Once all the skins are loose, I cut out the stem and tough part of the inside and pull off the skin. Placing the tomato on a cutting board, it gets cut into small pieces.
This, of course, is the “proper” way to cut up the tomatoes, but I often do the more “hands on” approach. Making sure that I have clean hands, I stand above the compost bucket, pull off the skins and mush the tomatoes into a bowl with my hands and through my fingers (removing the stem and tough interior).
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. Continue heating and stirring 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 pot to boil gently for 5 minutes.
Canning the Tomato Mixture
Wash the canning jars and lids and place aside. Jars get used year after year, but lids can only be safely utilized once. Fill a water bath canner about ¾ full of water. Place a closed jar in the canner and make sure that there’s at least 1 inch of water above the jar. Add more water if necessary, remove the jar, and set the canner on the stove to boil.
Next, line up the jars and add the acid ingredient 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, we are ready to continue. With the jars lined up on the counter and the acid added, I ladle my tomato mixture into each jar, using a funnel to prevent spillage. 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 (tightly), and prepare for processing.
Processing the Jars
Once the jars all have lids, carefully place them in the water bath canner with jar “tongs.”
Make sure that everything continues at a soft boil and that there is at least 1 inch of boiling water above the top of the jars. Put the cover on the pot and start timing the processing. Processing takes longer at higher altitudes; 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, 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. With a nice trivet on the table or counter nearby, I slowly take out each jar (again with the “tongs”) and place it to cool. Be sure that the trivet is 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 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. I take off the screw bands (carefully) because they sometimes get food on them and leaving them on makes them rust. They 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!
If you need more advice on how to can your vegetables, or are looking to can more than just tomatoes, try our vegetable canning guide. 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!