Canning tomatoes: How to preserve your end-of-summer bounty

By Evan Kleiman

Tomatoes are plentiful and delicious at the end of summer. Can them to create a shelf-stable product. Photo by Shutterstock.

You see the videos on YouTube and TikTok: families in Italy and the U.S. coming together to process and preserve bushels of tomatoes on one hot day at the end of summer when tomatoes are plentiful and delicious. I’ve been joining in this ritual for about a decade with my friends Kazi Pitelka and Royce Burke.

Let me say right off the top that canning food so that it is shelf-stable is a process with rules you must follow. I took a private class to learn how to do it, and then I partnered with a much more experienced friend for the tomato canning extravaganza. Tomatoes are considered a high-acid food, so they can be water bath canned, which some see as the simpler of the two methods: water bath canning and pressure canning. However, tomatoes are on the edge of what is allowed acidity-wise. To ensure food safety, we add additional acidity to each jar using lemon juice, vinegar or citric acid. Some resources to begin to understand the canning process can be found at the National Center for Home Food Preservation, the Ball jar website,  and countless YouTube videos like this one.

The first step in our tomato canning extravaganza is to acquire cases of tomatoes direct from the farm. Photo by Evan Kleiman.

There are two distinct operations one undertakes to process tomatoes. There is the preparation of the fruit (yes, tomatoes are a fruit), depending on the product you want: whole tomatoes, puree or sauce. And then there is the canning process itself which results in a shelf-stable product.

I highly recommend taking a hands-on class to learn how to can. If there are no classes where you are, I suggest watching lots of YouTube videos to familiarize yourself with the tools and methods before you start dealing with hundreds of pounds of tomatoes. 

Jars filled with tomato sauce are in the canner, ready to be boiled to create a shelf-stable product. Photo by Kazi Pitelka.

Start by teaching yourself with five pounds of fruit, even using winter tomatoes to practice. There are many different ways of preparing the tomatoes and the sauce for canning. If you choose to use a tomato mill or even a simple food mill, the most common way of preparing the tomatoes is to boil them first, whole or cut in halves. Boiling causes the tomatoes to release juice and gives you a thicker product right out of the mill. In Italian, this product is called “passata,” and is simply the pureed tomato with no skin or seeds. Salt is added to the jars. This year we used two cases of paste tomatoes to make passata.

Our group chooses to make two sauces each year: “pomodoro” seasoned with garlic and salt and cooked down with olive oil; and “puttanesca” made with pureed anchovies, kalamata olives, capers, garlic and olive oil. We puree the piquant ingredients rather than leaving them whole or chunky for food safety reasons. We put the tomatoes through the mill raw, then cook the resultant thin puree down into sauce. 

Pureed tomatoes cook down into sauce on a camp stove outdoors. Photo by Evan Kleiman.

When you’re canning hundreds of pounds of tomatoes, the tomato mill is an important tool. It may be hand-cranked or electric, but it separates the skin and seeds and stringy bits from the pulp and juice of the fruit. I was incredibly lucky to have been gifted a fantastic machine many years ago that is still going strong. You can see my friend Kazi using the mill here.

Usually Kazi pulls hundreds of pounds of tomatoes off her plants for processing. As she harvests the different varieties, she freezes them in enormous zip-top bags to wait for the day. Freezing the tomatoes gives the same result as boiling them. When they thaw, the excess liquid pours out of the tomatoes. We choose to add some of this liquid back into our sauce for flavor. But this year, Kazi’s tomato crop didn’t produce enough. It happens. So we turned to Weiser Family Farms and Finley Farms. They both had San Marzanos in the quantity that we needed. Since Kazi doesn’t grow paste tomatoes, we’d never canned this variety before. It was enlightening. 

Working through the day requires stamina. Most people who drop by to “help” are surprised by how physical the task is. We spent 10 hours processing and canning 365 pounds of paste tomato varieties from Weiser Family Farms and Finley Farms into 60 gallons of sauce packed into pints, quarts and our favorite, 24-ounce jars. 

Happy canners pose after a day of processing and canning tomatoes. Photo by John Steinmetz.