In a 6- to 8-quart heavy pot combine the first four ingredients (through lemon juice). Bring to a full rolling boil, stirring constantly. Quickly stir in liquid pectin. Return to a full rolling boil, stirring constantly. Boil hard 1 minute, stirring constantly. Remove from heat. Quickly skim off foam with a metal spoon, avoiding peaches.
Ladle hot jam into hot, sterilized half-pint canning jars, leaving a 1/4-inch headspace. Wipe jar rims; adjust lids and screw bands.
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.