Simmering sour cherries with just enough sugar to balance their tartness is a simple way to make the fruit last. Store preserves in the refrigerator and stir them into yogurt or vanilla ice cream for a splash of summer.
In a nonreactive bowl, combine all ingredients. Let stand, stirring often, until fruit has begun to macerate, 1 hour. Place a parchment round directly over surface and refrigerate, at least 8 hours and up to 1 day.
Remove from refrigerator and let stand, stirring occasionally, 30 minutes. Strain mixture through a medium-mesh sieve, reserving solids. Place juices in a pot and bring to a boil over medium-high heat. Skim any impurities from surface, reduce heat to medium, and cook, skimming occasionally, until reduced by half and very syrupy, 16 to 18 minutes. Stir in reserved cherry solids. Return to a simmer and cook, gently stirring occasionally, until fruit is plump and just beginning to soften, about 3 minutes more. Let cool slightly, then transfer to jars. Let cool completely, then cover and refrigerate up to 1 month or try canning with our helpful instructions.