Blueberry Jam

Ingredients

Instructions

1. 1Wash 8 half-pint jars in hot, soapy water or run them through the dishwasher, and keep them hot until filling time; pre-boiling is not necessary since the process time below is 10 minutes.
2. 2Simmer the new lids in a small pan of hot water (do not boil) according to the manufacturer's directions, and keep them warm until needed.
3. 3Wash the screw bands in warm soapy water and set aside at room temperature.
4. 4Rinse 3 pounds of fresh blueberries, discard any stems or soft berries, and crush them in batches with a potato masher until you have 5 cups of crushed fruit (a few chunks of skin are fine).
5. 5In a large saucepot, stir together the 5 cups of crushed blueberries, 1/4 cup bottled lemon juice, and the full box of powdered pectin; add the optional 1/2 teaspoon of butter to help reduce foaming.
6. 6Bring the mixture to a full rolling boil over high heat, stirring constantly, then stir in all 6 1/2 cups of sugar at once.
7. 7Return the mixture to a full rolling boil that cannot be stirred down and boil hard for exactly 1 minute, stirring constantly.
8. 8Remove from the heat and skim off any foam with a metal spoon.
9. 9Ladle the hot jam into the hot jars, leaving 1/4 inch of headspace.
10. 10Remove air bubbles with a non-metallic spatula, wipe the rims clean with a damp cloth, center a warm lid on each jar, and apply a band until fingertip tight.
11. 11Process in a boiling-water canner with jars covered by 1 to 2 inches of water: 10 minutes for half-pints and 10 minutes for pints, timed from the moment the water returns to a full rolling boil.
12. 12Add 5 minutes of processing time at 1,001-3,000 feet elevation, 10 minutes at 3,001-6,000 feet, 15 minutes at 6,001-8,000 feet, and 20 minutes above 8,000 feet.
13. 13After processing, turn off the heat, wait 5 minutes, then remove the jars to a towel-lined surface and let them rest undisturbed for 12 to 24 hours.
14. 14Check that each lid is concave and firm (not flexing) once cooled; remove the bands, wipe the jars, and label with the contents and date.
15. 15Store in a cool, dark place for up to 1 year for best quality, and refrigerate after opening, using the jam within about 3 weeks.
16. 16Do not alter the proportions of fruit, sugar, lemon juice, or pectin, since changing this ratio can affect both the safety and the set of the jam.