Stir in sugar. Return to a full rolling boil and boil exactly 4 min., stirring constantly. Remove from heat. Skim off any foam with metal spoon.
Pour off into prepared jars and process in a water bath per canning instructions. (below).
Spoon 2 tablespoons of mixture onto a chilled plate. Run your finger through the mixture to see if it sets (meaning it will gel easily). Here you’ll notice that the liquid slowly comes back together. This means it will not set. Continue boiling for 2 to 3 more minutes.
Ladle immediately into prepared jars, filling to within 1/8 inch of tops. Wipe jar rims and threads. Cover with two-piece lids. Screw bands tightly. Place jars on elevated rack in canner. Lower rack into canner.
Pour off into prepared jars and process in a water bath per canning instructions.
Wash empty, wide-mouth jars and lids in warm soapy water and rinse well. Sterilize the jars and lids with boiling water. You can reuse jars but it is best to buy new lids for each batch of canning. Rubberized, two-piece canning lids are best.
Fill the sterilized jars to 1/4″ from the top. Wipe each jar rim with a clean paper towel. Place a lid on each jar and screw it on. The seal should be firm but not too tight. The seal must allow steam to escape during the heating process but should be so loose as to allow fresh air to seep inside.
Place the jars in a hot-water canner or a pressure canner. Heat the jars inside the canner for the recommended time. (Water must cover jars by 1 to 2 inches. Add boiling water if necessary.) Cover; bring water to gentle boil. Process 10 minutes. Remove jars and place upright on a towel to cool completely. After jars cool, check seals by pressing middles of lids with finger. (If lids spring back, lids are not sealed and refrigeration is necessary.)
Wipe the cooled jars with a damp towel. Store in a dark, cool, dry place.