Strawberry-Rhubarb Slow-Cooked Jam

When grandson Archie and his parents visited in June 2020, we picked strawberries at a U-Pick farm down the road. We have plenty of rhubarb growing in our garden. Strawberries and rhubarb are ready to pick at about the same time, so this recipe was a perfect match. It uses no added pectin and about half as much sugar as most strawberry jam recipes.

Have ready:

1 1/2 pounds fresh strawberries, stemmed and halved
3 3/4 pounds rhubarb stalks cut into half-inch slices
4 1/2 cups sugar
3 tbs. fresh lemon juice

Choose a heavy pot of at least 5 quarts. I use a 5.5-quart Staub cast-iron Dutch oven, which is barely large enough. Put all the ingredients into the pot and turn on the heat to just a bit above medium. Resist the urge to bring everything to a boil by cranking up the heat to max. There is a danger of burning at very high temperatures. I use number 6 or 7 on my 9-point electric stovetop.

Stirring will be lumpy and difficult at first, but begin stirring almost immediately. Within the first 10 minutes or so, the hot rhubarb will soften and the fruit will release more liquid. The stirring will become noticeably easier.

When you see the first bubbles indicating that the mixture is nearing the boil, turn the heat down to the low side of medium. I use the number 4 setting. The idea is to find a temperature that just barely sustains a boil. If you lift your stirring spoon out of the pot and see a bubble almost immediately, that’s perfect. But keep stirring.

Here’s the tough part: Stir constantly for at least an hour. Yes, stir for an hour. You will see the jam change over time. The individual pieces of strawberry and rhubarb will disappear, the mixture will thicken somewhat, the level in the pot will fall (I lose more than an inch in the Staub), and the color will darken. The long cooking will thicken the jam and the lemon juice will sustain some of the fruit’s natural pectin, which weakens with cooking.

Continue cooking and stirring — 90 minutes is not out of the question — until you reach the desired consistency (Frau Erica’s undefined gewünchter Konsistenz). A couple tests can help determine when your batch has reached that point. You can insert a thermometer to see if the jam has reached 205°F and/or you can dip a clean metal spoon into the jam and see whether the jam coats the spoon thickly enough.

Remove from heat. Fill into sterile one-cup jelly jars, place caps, and screw the rings on finger-tight. Process in boiling water for 10 minutes, then remove from the water. Set the jars on newspaper to cool undisturbed for at least eight hours or overnight. The recipe yields nine or 10 jars.

About canning

A pot wide enough to process 10 jelly jars is essential. I use an old brewing kettle set on a propane burner in the back yard. I fill it with water, insert a rack with 10 jars in it and let it boil while I cook the jam. The jars are perfectly sterile when I fill them. Use new lids. No need to boil them, but put them in a pot, pour boiling water over them, and let them sit until it’s jar-filling time.