Karl’s Thomcord Grape Jam

I found a new produce—new to me at least—at Trader Joe’s this week, Thomcord grapes. These grapes are a crossbreed of Thomson seedless and Concord grapes. They have dark purple skins and a wonderful flavor. While my wife Jan does not like grape jelly—growing up her mother bought nothing but Welch’s grape jelly—daughter Eilene loves it. She asked me to turn these grapes into a jam.

Karl’s Thomcord Grape Jam

Karl’s Thomcord Grape Jam

The last time I made grape jelly it was only a limited success—it was so unspectacular that I never posted it. I had remove the peels and the results had only a modest grape taste—much of a grapes flavor is in the skin. A few weeks ago, I was experimenting with blending and sieving small tomatoes to produce tomato sauce. I thought that this technique would work with these new grapes.

Note: While many recipes have you peel tomatoes to make a sauce, the results are pale pink rather that a deep red color. The problem I had was that the tomatoes I had been gifted were too small to peel and seed—I had to find another way to process them. As well as improving the color, keeping the skins also adds substantial flavor and vitamins.

While many recipes call for adding lemon to their grape jams, I did not want to muddle the grape flavor. However, this also reduces the amount of pectin needed for a good “jell.” I decided that I would unbend and use commercial pectin to set my jam.

Note: This was an experiment, so I started with a very small batch that produced just a little more than two 8 oz. jars of jam.

Karl’s Thomcord Grape Jam


1 lb. Thomcord grapes (about 2 ½ cups blended)

1¼ cups sugar, separate uses
Pinch Kosher salt

1¼+  Tbs. commercial pectin


1. Sterilize three 8 oz. canning jars and lids.

2. Rinse, stem, and pick through the grapes.

Tip: Discard any grapes that have soft spots. In fact, discard any grape that you would not personally eat right that moment—yes, I know it is hard not to snack, but resist the temptation.

Note: My philosophy on this point is that: You should cook like you were going to eat each bite of the dish yourself.  I am deeply disturbed when I get a restaurant dish with mushrooms where the dried out stems have not been trimmed off. It is clear that the cook knows that they are cooking for someone else and does not care what their diners put in their mouths.

3. Put about half of the grapes in a standing blender and process them for two minutes.

Tip: This liquefies the grapes enough that the blender has something to work with.

4. Add the rest of the grapes and process the grapes for 4-5 minutes.

Tip: You are trying to get the blender blades to chop up the skins as much as possible.

5. Pour about a cup of the grape slurry into a wide mesh sieve and press the juice through with a spatula.

Tip: While these grapes are “seedless” there are still some immature seeds that you wish to screen out. You want your sieve to be in the “Goldilocks” zone—not to big, not too small.

6. Scrap any bits of grape skin that does not fit through the mesh and return it to the blender.

Tip: The idea here is to break down the skins as much as possible. As you reduce the amount of liquid in the blender, the whirling blades have more contact with the remaining bits of grape skin.

7. Process the grapes for another few minutes.

8. Repeat the sieving  with a second cup of the slurry.

Tip: Scrape out the skins and return them to the blender.

9. Continue processing the remaining slurry and sieve the rest of the grape juice.

Tip: Discard the last of the grape skins that fail to go through the sieve.

Note: Scrape the bottom of the sieve and give it a good rap on the side of the pot to free the last of the grape liquid.

10. Add the sugar and salt to the grape juice and bring it to a boil.

Tip: You do not want to add so much salt that your jam tastes salty, but just the smallest amount of salt enhances the flavor of sweet things—think putting salt on watermelon.

11. Reduce the heat and cook the grape juice and sugar over medium low heat for 10 minutes.

Tip: If you wish you may stop cooking your jam at this point—you will get a “fresher” fruit flavor, but to get the jam to jell properly you will need to add as much as three tablespoons of pectin. Cook the jam another five minutes after adding the pectin.

Note: I like to cook my jams for an extended period—30-40 minutes—it caramelizes more of the sugars and give the jam a deeper flavor. The longer cook also evaporates more of the liquid and the jam will require adding less commercial pectin to set up your jam.

12. Add the pectin and simmer the jam to your liking, this can be anywhere from 30 minutes to  an hour—depending on how juicy your fruit was and exactly how high you have your heat.

Tip: Take a spoon of the juice and place on a plate next to an ice cube. After a few minutes pour the juice back into the pot. When the juice flows off in a sheet—rather than a thin stream— the jam is ready.

Note: Start with one tablespoon of pectin and simmer the jam for five minutes. If it is still not setting to your satisfaction add more a bit at a time. If you add too much pectin your jam will come put more “pasty” rather than “jam-y”

13. Pour the grape jam into sterilized jars and loose tighten the lids.

Tip: Put the lids on the jars and tighten them down. Back the lids off about an eight of a turn so that they are “tight/loose.” This allows the air to escape—when you reheat the jars in a water bath—but does not let the water leak into the jars.

Note: If you wish to extend the shelf life of your jam—not really an issue at my house—put the partially sealed jars in a water bath and boil them for another half hour to finish the “canning” process.

15. Place the jam jars in a water bath and boil for 20-30 minutes.

16. Remove the jars and fully tighten the lids.

17. Allow them to cool completely before storing.

Tip: The jam should last for a year on a pantry shelf, but you will be lucky if it sees the next month.


Filed under Breakfast, Treats, Vegan, Vegetarian

3 responses to “Karl’s Thomcord Grape Jam

  1. Laurel

    How did it turn out? I’ve never made jam before and will have to buy all the equipment and pectin to do this, so I want to know if it’s really worth it. I love the taste of grape jam and juice made from Concord grapes, so I got excited about trying Thomcord grapes at TJ’s. The flavor of the raw grapes isn’t quite as intense as I’d hoped, though, and they’re getting overripe in my fridge. I figured the flavor will be stronger if I make a jam! I probably wouldn’t use a sieve at all; I don’t mind bits of skin or tiny seeds. I want to make a jam with less sugar anyway (probably subbing some of it with xylitol or some other healthy-ish sweetener). But I’d really like to know if gives you a somewhat stronger Concord flavor than the raw Thomcord grapes did. Thank you so much in advance!!

    • karllueck

      Res it is worth it! The heat of cooking the jam mellows the raw grape flavor and being crossbred with the Thompson grapes means that there are virtually no seeds.

  2. Jean Steer

    Thanks so much for this recipe. I’ve been canning for many years, but never grape jam. I have one large Thomcord grape vine. This year it was full of grape bunches. I used your recipe to make 9 batches(4 8oz jars each) of jam. Each turned out great. Again thanks for a good and easy recipe!

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