Tomato and onion jam

I really like making my own condiments and sauces because a) it’s often inexpensive and uses ingredients I already have on hand and b) many sauces and condiments at the grocery store have high fructose corn syrup and high amounts of sugar in them.

I decided to make tomato jam because I had a serious, serious surplus of green (and some red) tomatoes from my garden. It’s definitely autumn here, leading in winter. This weekend, I finally conceded that it’s not going to get up to 70 degrees anytime soon, so it’s time to pull the rest of the fruits off the tomato plants and do SOMETHING with them.

I didn’t set out to limit the amount of sugar in this recipe, but it sort of happened that way on its own. This recipe is time-intensive because it uses caramelized onions, reduced balsamic vinegar, and reduced tomatoes. The end result was tangy with a sour bite (from the vinegar and tomatoes) but also with a prominent sweetness.

The recipe does contain a little sugar, added toward the end. But that’s a matter of personal preference so I recommend tasting throughout and adjusting based on your preferences or dietary needs.

What can you use tomato jam for?

It’s relatively new to me, too.  It’s a savory jam, and I’ve found it’s awesome on crusty bread.  It’s awesome with cheese.  It’s awesome as a stand-in for ketchup.  It’s even awesome off of a spoon.  It’d probably be awesome tossed in pasta with olive oil and bits of cured meat.  Sky’s the limit, really.  Maybe I’ll make a PB&J and tell you how that goes.  ;D

5.0 from 1 reviews
Tomato and onion jam
Recipe type: Condiment
Prep time: 
Cook time: 
Total time: 
Serves: 6-8
This recipe yields about 24 ounces of jam (about three small mason jars' worth).
  • 1.5 lb tomatoes, roughly diced
  • 5 tbsp oil
  • 1 medium yellow onion, thinly sliced
  • 6 cloves of garlic, thinly sliced
  • ¼ cup balsamic vinegar
  • ⅓ cup water
  • 1 heavy tsp fennel seeds
  • 2 tsp sugar
  • 1 tbsp salt (or slightly more/less — you'll be tasting throughout the jam-making process)
  1. Add the oil to the bottom of a skillet or sauce pan over medium heat. I didn't use non-stick. Ideally, the pan would have a large surface area to help the caramelization move along faster. Through in onion and sprinkle with some salt.
  2. Stay on medium heat until the onions are translucent. Once they get to that point, lower heat to low.
  3. It will take a while (the whole caramelization process takes about 45 minutes) but at some point, your onions will start to stick a little to the bottom of the pan and get brown at the contact point. Diligently scrape the bottom of the pan to keep the onions from getting burned and to distribute the the caramelized onion sugars throughout the whole mixture. Be sure to spread out the onions after each scrape, instead of leaving them all in a lump in the middle.
  4. Sometimes the caramelized bits from the onions won't detach from the spoon. I find using two spoons helps. One scrapes; the other detaches the awesome onion goo.
  5. Toward the end of the 45 minutes, the onions will caramelize a lot faster. Turn down the heat, if possible, and stay constantly on top of the pan, stirring and scraping.
  6. Once your onions are nice and brown and delicious, add in the tomatoes, garlic, balsamic vinegar, and the water. Return to medium-high heat and scrap the bits still on the bottom the pan.
  7. Once the mixture bubbles and just about starts to boil, reduce the heat to medium low and keep it at a simmer.
  8. Meanwhile, roast your fennel seeds in a dry pan over medium heat, until they are fragrant and slightly brown. Crush them with a mortar and pestle (or leave them whole if you don't have the set-up and don't want to drag out another appliance). Add them to the jam.
  9. Let the mixture reduce and reduce and reduce, until it's thick and holds itself up as a lump on a spoon. It will take an hour or more. The mixture should darken. The tomatoes should disintegrate a fair bit, with some chunks here and there.
  10. Salt once again, to taste. It's a sourish condiment, so it needs the salt to stand up against and display its layers of flavor. If preferred, add some/all of the sugar.
  11. Let the mixture cool a little bit before added to jars/containers. Store in the fridge when not using. It will store for up to a month.


These are the sorry plants from whence the tomatoes for this recipe came.  As you can see, you don’t need to use the best of the best heirlooms for this jam.  (In fact, I totally don’t recommend it because the tomatoes lose much of their individualistic tomatoey-ness during the long simmer and reduction.)  If you have cruddy tomatoes lying around that don’t taste great raw, they are great for this recipe.  Incidentally, I should mention that the presence of onions in this recipe was to help out my cruddy green tomatoes in the sweetness department.  They did that and more!

I used a plain ol’ yellow onion.  I imagine that some people might wonder if Walla Walla onions would be good in this recipe.  The answer?  Probably, due to the higher sugar content.  But Walla Wallas are pricier.  Is it worth it?  Not really.  Any and all onions will caramelize.  By the time you get to the luscious brown onion goo, there’s no way you can taste it and tell what kind of onions were used.

The caramelized bits on the end of a spoon.

OMG, you could just eat this by itself and it would be awesome.

Fennel seeds are my love.  They have an anise-y flavor.

Tomato jam “before.”

Tomato jam “after.”

Jam is a marketized term these days.  There’s all these food items that are being called jams, like bacon jam.  When I started this recipe, I wondered: What is jam? What makes something authentically jam? Can bacon really be made into jam?

It was all very Existentialist.

The answer to those questions is a bit complicated and non-definitive. The U.S. FDA has defined jam and jelly in very specific and mathematical terms (such-and-such percentage of juice to fruit to water to sugar = jam/jelly); it also uses jam and preserve interchangeably, for the most part. While interesting, the FDA’s definitions did not matter much to me because the FDA wasn’t really using the terms in the way that we usually use the terms. Also, the FDA wasn’t comprehensive in its definitions. It didn’t tackle other fruit spreads like marmalades or curds, for instance.

The more I looked into, the more I thought, dude, this information would make a good infographic.

(Click for more of my food-related infographics.  For other food-related infographics, visit my Pinterest board.)

I based my definitions around what is the most commonly accepted definition in the U.S. There are slight deviations for Brits (much like how our cookie is their biscuit), but on the whole, it’s in the general vicinity.

I’ve decided that bacon jam is not really a jam, but a relish or a paste. I’ve decided that jam has to be mostly made of plant-based ingredients because fruits and veggies naturally contain pectin, the primary gelling agent in jams and jellies.

  • Steph

    Just wondering if you skinned the tomatoes before cooking?

  • This looks so good and the recipe sounds even better. I’m going to try this tomorrow. I bought heaps of end of the season tomatoes at the market today.

    • Thanks, Maureen! I hope it turns out well!