As a fruit for preserves, the blueberry is tenacious. The taut globes hold their shape relentlessly — a quality appreciated in pie when, after a time in the hot oven, the berries burst gently. In the case of jam, the sturdy skins are a beneficial source of pectin and need a good squashing to activate their necessary properties.
I like to add to the jam the citrusy herbal charm of lemon verbena: subtle, so it elevates the blueberry flavor without interfering. I stir in just enough to balance the natural tartness of the fruit. Use your judgment while sweetening the jam, tasting to understand the sweet and sour of your blueberries.
Develop the flavor of the jam by macerating the berries; then, use a potato masher or a sturdy spoon to crush them. The mixture is ready when it has some heft, with a few remaining whole berries suspended in it. Cook it quickly over high heat, so the water content reduces and the gel builds.
That’s it. Blueberry jam is satisfyingly straightforward.
The jam will firm up further as it cools, so remove it from the stove before it seems done, then let the jam sit and cool for a few minutes before checking the gel. Return the pan to the stove and continue cooking if the jam still seems too loose.
Be prepared: Kitchen towels, wooden spoons, aprons and more may be sacrificed to murky, deep purple stains. This is a gloriously messy process.
A dollop of blueberry jam and a dram of good gin — stirred well, poured over ice and topped with sparkling water — makes a delightful way to end a day of canning.
Canning Class appears twice a month. Barrow’s first cookbook, “Mrs. Wheelbarrow’s Practical Pantry: Recipes and Techniques for Year-Round Preserving” (W.W. Norton), will be published in the fall. She blogs at www.mrswheelbarrow.com. She will join Wednesday’s Free Range chat at live.washingtonpost.com.
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