1. In a medium heavy saucepan combine cranberry juice, vinegar, and the serrano peppers. Bring to boiling; reduce heat. Simmer, covered, 10 minutes. Strain mixture through a fine-mesh sieve set in a medium bowl; discard peppers. Measure 2 cups liquid.

2. In a 5- to 6-quart heavy pot combine the 2 cups strained liquid and the sugar. Bring to boiling over medium heat, stirring constantly to dissolve sugar. Quickly stir in pectin. Bring to a full rolling boil, stirring constantly. Boil hard 1 minute, stirring constantly. Remove from heat. Quickly skim off foam with a metal spoon.

3. Ladle hot jelly into hot, sterilized half-pint canning jars, leaving a 1/4-inch headspace. Wipe jar rims; adjust lids and screw bands.

4. Process filled jars in a boiling-water canner 5 minutes (start timing when water returns to boiling). Remove jars from canner; cool on wire racks.

Up the Heat

For a hotter jelly, stir in serrano chile pepper slices with the pectin. Evenly divide the pepper slices among the jars.