Fresh Tomato and Caramelized Onion Jam Recipe

The bright, sweet, and tart flavor of in-season tomatoes preserved for the fall.

Two slices of bread topped with tomato and onion jam on a ridged cream colored ceramic plate. In the left corner of the image is a glass jar filled with more jam, and in the top left corner is a portion of another plate with more toast on it.

Serious Eats / Mariel De La Cruz

Why It Works

  • Using inexpensive Roma tomatoes results in an intensely flavorful jam.
  • Sweetening the jam with caramelized onions adds another savory dimension.
  • Peeling the tomatoes first yields jam with a smooth, uniform texture.

"This is a tomato? I thought it was a heaven ball," exclaims Luanne, prompting a quick reply from Hank that "tomatoes don't have any flavor," who is left eating his own words after one bite. I felt a close affinity to that King of the Hill episode, which found the all-American Hank Hill forced into the hippie hell of a co-op, only to discover the beauty of vegetables and meat that exist outside of the average supermarket.

I had a similar revelation many, many years ago when I first joined a CSA and found that tomatoes can be an incredible explosion of complex sweet and tart flavor, with a luscious texture that bridges a line between soft, juicy, and crisp. Prior to that, I'd only seen tomatoes as a nuisance—adding no flavor and an unappealing mealy texture to otherwise excellent sandwiches, burgers, and salads.

So, when it comes to prime tomato season in late summer here in New York, I rejoice in the harvest and become excited each time an opportunity arises to chow down on delicious farm fresh tomatoes. Of course, the party has to end, and with that day drawing near, I was left pondering ways that I could extend the peak of the best tomato flavor and thought a jam would fit the bill quite nicely.

Choosing the Ideal Tomato

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Serious Eats / Joshua Bousel

I've come to appreciate not only the tomato, but the unique qualities of the seemingly endless varieties that have graced my table. Each possesses a unique character, as well as best uses. To start out my jam, I first had to figure out which type of tomato would be the best fit.

Most recipes I've seen for tomato jam call for Roma tomatoes, but might a more robust and sweeter heirloom variety make for a better jam? What about the smaller specimens like grape or cherry? Might that pairing of sweetness and acidity make a more interesting and layered jam? Or maybe the process of boiling the tomatoes into oblivion with a hefty amount of sugar leaves the question of variety one of little consequence?

To answer these questions, I moved ahead with three different tomatoes—heirloom, a mixed bag of small tomatoes, and run-of-the-mill Romas.

Sweet Onion

Too many jams are pure sugar, with just a mild fruity accent. The better ones, though, can deliver that sweetness while still retaining the essence of the fruit, which is what I was looking for in a tomato jam recipe. I wanted to coax a more natural flavor out of mine, so in seeking to lessen the load of white sugar, I thought caramelized onions would be a good place to turn. The natural sweetness developed in the onions meant that I could scale back the amount of plain sugar needed—plus I love caramelized onions on just about anything and think they pair excellently with tomatoes.

I started my jam process by making a Dutch oven full of caramelized onions, following Kenji's 15-minute method, which admittedly ended up being not quite as quick due to the large volume (I needed to have enough to split into at least four jams). Still, cooking down three pounds of onions until softened and browned clocked in at under an hour, which isn't bad compared to the two or three hours it takes when I'm using a more traditional method for French onion soup.

Looks A-peeling

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Serious Eats / Joshua Bousel

As I simmered down my first two batches of jam—mixing the tomato and onion with lemon juice, cider vinegar, white sugar, brown sugar, salt, and a little crushed red pepper—I noticed they were littered with bits of peel that didn't break down. Those skins didn't bother me that much in the end, but for round two, I thought I might improve the texture by peeling the tomatoes. I made quick work of this using the blanching method, but I'm also partial to the torch method, which requires less equipment to clean later.

Trying to go with a minimal amount of sugar in my first batch also left me with a jam that had a harsher acidity than I wanted. This had me adding more sugar the second time around, but I found upping the amount a mere quarter cup fixed the problem perfectly.

Jam Results

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Serious Eats / Joshua Bousel

Each of the four jams I made took just over an hour of simmering for the tomatoes to break down and the mixture to become thick and gelatinous. I tried adding some grated apple to one batch for some extra pectin power, but it made no real difference in texture or time, so I let that idea fall by the wayside.

Out of the lot, there was a clear loser—the jam with the small mixed variety tomatoes was way too overloaded with skins, making for an unappetizing experience. It was also more tart than the others, losing the subtle sweetness of the tomatoes altogether.

In the battle between peeled and unpeeled, the peeled tomatoes resulted in a slightly more cohesive jam. It was enough of a difference that I'd recommend peeling, but not so much that it needs to be strictly enforced.

The hardest question was whether the convenient and plentiful supermarket Romas would prove markedly inferior to the more elusive and expensive heirlooms. The heirloom jam had a sweeter and slightly more robust profile than the Romas, but the complexity and texture that made the heirlooms so desirable as a raw fruit was difficult to pinpoint in the jam. The Romas, on the other hand, made a jam that had a strong intensity of tomato flavor, one that was elevated a lot from their raw state, bringing them closely in line with the marginally better heirloom version.

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Serious Eats / Joshua Bousel

I say that if you can get away making an excellent jam on the cheap without the pain of ingredient hunting, that's the way to go, so the Roma tomato jam easily won the battle. It had a nice fruity flavor, thick and chunky jammy texture, a complex sweetness, and a slight tang that all came together to make me happy that I found a way to have a bit of that bright tomato flavor for just a little bit longer.

September 2013

Recipe Facts

4.5

(2)

Active: 30 mins
Total: 2 hrs
Serves: 16 servings
Makes: 1 cup

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Ingredients

  • 3/4 pounds yellow onions (about 2 medium), finely sliced

  • 1 tablespoon butter

  • 1 1/2 pounds Roma tomatoes (about 6 medium), peeled, cored, seeded, and finely chopped

  • 1/2 cup white sugar

  • 1/4 cup light brown sugar

  • 2 tablespoons juice from 1 lemon

  • 2 tablespoons apple cider vinegar

  • 1 teaspoon kosher salt

  • 1/2 teaspoon red pepper flakes

Directions

  1. Melt butter in a 3-quart stainless-steel saucepan or saucier or a 4- or 5-quart enameled Dutch oven over high heat. Add onions and cook, stirring frequently, until bottom of saucepan is glazed in a pale brown fond, about 5 minutes. Add 2 tablespoons water and scrape up fond with wooden spoon. Continue to cook, stirring frequently, until fond has built up again, about 2 minutes longer. Add 2 more tablespoons water and scrape up browned bits. Repeat cooking, adding water, and scraping until onions are completely softened and a deep, dark brown, about 15 minutes total.

    A four-image collage showing the onions being caramelized. The top-left image shows the onions in a large Dutch oven before they've been cooked. The top-right image shows the onions, partially browned, being stirred with a wooden spoon. The bottom-left image shows the onions, now darker in color and cooked more, being stirred by a wooden spoon. The bottom-right image shows the onions in the Dutch oven, now deep brown and soft.

    Serious Eats / Mariel De La Cruz

  2. Add tomatoes, white sugar, brown sugar, lemon juice, vinegar, salt, and red pepper flakes in with the onions; stir to combine. Bring mixture to a boil, then reduce heat and simmer, stirring occasionally, until tomatoes have broken down and jam has thickened and developed a jammy consistency, 1 to 1 1/2 hours. Remove from heat. Transfer jam to an airtight container and store in refrigerator for up to 2 weeks.

    A four-image collage showing the tomatoes being cooked down with the onions. The top-left image shows the chopped tomatoes added to the Dutch oven filled with onions. The top-right image shows the tomatoes and onions, cooked down further. The bottom-left image shows the tomatoes and onions now very cooked down and extruding liquid. The bottom-right image shows the jam now fully caramelized and reduced.

    Serious Eats / Mariel De La Cruz

Special Equipment

3-quart stainless steel saucepan or 4- or 5-quart enameled Dutch oven

Nutrition Facts (per serving)
59 Calories
1g Fat
13g Carbs
1g Protein
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Nutrition Facts
Servings: 16
Amount per serving
Calories 59
% Daily Value*
Total Fat 1g 1%
Saturated Fat 0g 2%
Cholesterol 2mg 1%
Sodium 88mg 4%
Total Carbohydrate 13g 5%
Dietary Fiber 1g 3%
Total Sugars 11g
Protein 1g
Vitamin C 8mg 39%
Calcium 12mg 1%
Iron 0mg 1%
Potassium 145mg 3%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
(Nutrition information is calculated using an ingredient database and should be considered an estimate.)