Prepare the red currants by either hand-stemming them to keep the seeds, or planning to run the cooked fruit through a food mill for a smooth, seedless jam.
Add a splash of water or juice to a saucepan to prevent scorching, then add the currants and bring to a simmer.
Stir in sugar to taste and let it dissolve.
Simmer just until the jam thickens and begins to set, only a few minutes. Pull it off the heat as soon as it sets, since red currants set hard if overcooked.
For seedless jam, run the cooked fruit through a food mill now. Ladle into prepared jars and refrigerate, or process in a water bath canner for 10 minutes with 1/4 inch headspace.
Notes
Fruit Amounts: One pound red currants is about 2 1/2 cups, or a heaping farmer's market pint. One pound of sugar is about 2 cups. My ratio by volume is 2 1/2 cups whole fruit to 1 cup sugar for best flavor and set.Yield: One pound of red currants makes about 1 half-pint jar. The recipe scales up easily to 4 to 6 pounds per batch.Sugar Amounts: Sugar is to taste and set here and doesn't affect canning safety. A 2:1 fruit-to-sugar ratio suits most people. For a classic, old-fashioned jam, increase the sugar to 1 pound fruit to 1 pound sugar for a sweet, store-style jam. Seeds or Seedless: Hand-stem and leave the seeds in for a chunkier jam, or run the cooked fruit through a food mill or sieve for a smooth, seedless one. Both set well.Batch Size: Unlike most jams, red currant jam scales up well because the high natural pectin sets the fruit fast. Stay at or below about 6 pounds per batch to keep the bottom from scorching.Frozen Currants: Cook them straight from frozen and skip the added water, since they release plenty of their own as they thaw.Sugar substitutes: Honey can change the gel and the flavor, and may scorch before it sets, but it will work in most cases. Just watch it carefully as you cook it. Sugar-free sweeteners like monk fruit won't set properly. Altitude Adjustment: Process for 10 minutes below 6,000 feet, or 15 minutes above 6,000 feet.