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Foolproof Preserving

How to Preserve Summer Tomatoes for Year-Round Freshness

There's nothing like a peak summer tomato. These tips will ensure you can enjoy them all year long.
By Published Aug. 16, 2017

Here in New England, tomato season is achingly, heartbreakingly brief. Perhaps that’s why I’m such a fanatic for summer tomatoes—when they finally come rolling off the vine and flooding the local farmers markets, I live almost exclusively on a steady diet of Caprese salads and sliced heirlooms sprinkled with salt.

But after these few glorious weeks, summer inevitably turns to fall, and fresh produce trickles out of the market as my tomato plants quietly give up the ghost.

Rather than face a winter of sad, tasteless supermarket tomatoes, I turn instead to my canner. A few days of hot work in the kitchen in August are more than worth it when in February I can reach for a glowing red jar in the pantry.

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Working on tomato recipes in the test kitchen for Foolproof Preserving was a total dream, as we found all of the best ways to capture the flavors of peak-season tomatoes and make them last year-round.

I usually start my preserving bonanza by picking up a case of plum tomatoes from a local farm and making a couple of batches of our Summer Tomato Sauce for serving over pasta all winter long. If I can persuade a few friends to join in, I put them to work with serrated peelers and chef’s knives to cut the prep time in half (and send them home with jars of their own to enjoy).

From there, a few batches of Roasted Tomato-Lime Salsa are a must, both for myself and for holiday gifts for friends. And lastly, I stock my bar with jars of our Bloody Mary Mix to warm up winter brunch gatherings. (Bonus, these Bloody Marys are even better served with homemade dilly beans canned earlier in the summer.)

In the end, canning is really a form of time travel. Opening one of these jars in the darkest days of winter brings me all the way back to August and its bright, fresh flavors. Hopefully I’ve made just enough jars to get me through to late summer next year, when this (delicious) cycle will start all over again. (Looking for more information about canning? We have everything from a step-by-step guide to canning to the science behind canning in our book Foolproof Preserving.)

Here are some tips for canning tomatoes.

1. Choose the Best

When picking tomatoes, choose the freshest you can find. Ones that are locally grown tend to be the most flavorful. Choose tomatoes that are fully ripe, smell fruity, and feel heavy. Make sure they don't have any bruises or cracks because those can harbor hidden mold or bacteria that can ruin your processed jars.

We tested all manner of tomatoes during our recipe development and liked plum (often called roma) tomatoes the best. They taste sweet with a strong tomato flavor and are the perfect combination of juicy and sturdy. Their size makes them easy to pack into jars and they really hold their shape well.

Big beefsteak tomatoes were less juicy, with a firmer structure. They took longer to break down in recipes, so we ended up cutting them into smaller pieces. We also found beefsteaks to be less flavorful than plum tomatoes. Heirloom tomatoes encompass so many types that it is hard to generalize about them. We did not test our recipes using either grape tomatoes or cherry tomatoes. 

2. Acidify the Jars

Tomatoes vary widely in natural acidity and ride the pH borderline (4.6) between high and low acid foods. In order to ensure a safe pH level for boiling water canning, we add bottled lemon or lime juice or vinegar to the hot jars before adding the tomatoes to up their acidity. (We use bottled juice, which has a consistent pH, instead of fresh lemons or limes, which can vary in acidity from lemon to lemon.)

3. Peel the Tomatoes

If you don't have a serrated peeler to peel your tomatoes, here's how you can easily remove the skins using the old-school method of blanching the tomatoes in a pot of boiling water. Here's how.

1. Remove core and score small X in bottom of each tomato.

2. Add no more than 6 tomatoes (any more and the water temperature drops too low) to large pot of boiling water; boil just until skins loosen, 15 to 60 seconds. Using slotted spoon, transfer tomatoes to ice bath to cool, 2 minutes.

3. Remove tomatoes from ice bath and remove loosened tomato skins. Return water to boil and proceed with next batch of tomatoes.

4. Be Aware of Processing Time

Because tomatoes are dense, they require longer processing times: 80 minutes and up. Thickness and density are factors in how heat permeates a filled jar's contents and contribute to determining the processing time.

Tomatoes have more available moisture, making it easier for bacteria to grow, so the pH and longer processing times are critical to ensure safety. We discovered that using pint jars instead of quart jars for our tomato sauces allowed us to shorten the processing times for the sauces.

5. Mind the Gap

Tomatoes are watery and as they heat, they release their juices along with air. During processing and cooling a harmless air gap can occur in the jars. Hot-packing minimizes this, because air is released during the precooking of the tomatoes—but an air gap can still occur.

We tested increasing the headspace in quart jars of whole tomatoes and found that leaving 1½ inches was best. If a large gap appears at the top of the jar but the lid is still fully sealed, the food inside the jar is still safe to eat. Be sure to wipe off any sticky residue from the jars before storing them and check the seal again before opening.