4 cups crushed blackberries (about 1-1/2 quarts whole berries)
2 tablespoons lemon juice
1 box (1-3/4 or 2 ounces) powdered pectin
6 cups sugar
Wash 6 half-pint jars. Keep hot until needed. Prepare lids as manufacturer directs.
In large, non-aluminum pot, combine the crushed berries, lemon juice and pectin. Bring to a full rolling boil over high heat, stirring constantly. Quickly add sugar, still stirring. Return to a full rolling boil that cannot be stirred down; then boil, stirring, for 1 minute. (If using a 2-ounce box of pectin, boil for 2 minutes.) Remove from heat and skim off any foam.
If preparing jam for the pantry, ladle into one hot jar at a time, leaving 1/4-inch headspace. Wipe jar rims with a clean, damp cloth. Attach lid. Fill and close remaining jars. Process in a boiling water bath for 10 minutes (15 minutes at 1,000 to 6,000 feet; 20 minutes above 6,000 feet).
If preparing for freezer or refrigerator, ladle the jam into clean jars (or freezer containers, leaving 1/2-inch headspace); apply lids. Let stand for 12 to 24 hours at room temperature; freeze or refrigerate.
Makes about 6 half-pints.
Storage Time: Processed, up to 1 year; unprocessed, up to 1 month in the refrigerator or up to 1 year in the freezer.