Many people use pectin to set their jams and jellies, and that’s a fine method. But chef Jason Bond prefers to let the natural pectin in the fruit do the work for him. You’ll get a slightly looser jam but brighter plum flavor. Red wine adds depth and color.
Put a porcelain or ceramic plate in the freezer to chill. Meanwhile, combine all ingredients in a 5- to 6-quart heavy-bottomed pot over medium-high heat.
Bring to a simmer so that the plums release their juices. Let cook 5 more minutes. Then pour mixture into a strainer set over a bowl, and press on the solids to extract the juice and fruit.
Return extract to heat and simmer, stirring often, 25 minutes. Reduce heat as needed to keep from boiling up. Remove the chilled plate from the freezer and spoon a small amount of jam onto it. It should thicken when it hits the cold. If it’s thick enough, stop there. If not, return the plate to the freezer and continue cooking the puree, checking it at 5-minute intervals, until it reaches the desired thickness (it should form a skin when chilled). Pour into hot, sterilized jars to within ¼ inch of the top, adjust lids, and process in boiling water 5 minutes. Let cool at room temperature and check seals.