Plum Jam

Ingredients

Instructions

1. 1Wash 6 half-pint jars in hot soapy water or the dishwasher and keep them hot; the jars do not need pre-boiling since the process time below is 10 minutes or more.
2. 2Simmer the new lids in hot (not boiling) water per the manufacturer's directions and keep them warm.
3. 3Wash the screw bands in warm soapy water and set aside.
4. 4Wash 4 pounds of ripe plums, cut in half to remove the pits, and chop the fruit, leaving the skins on for both color and natural pectin, to yield about 6 cups.
5. 5Combine the chopped plums, 5 cups of sugar, and 2 tablespoons bottled lemon juice in a large, heavy nonreactive pot, and let stand 30 minutes, stirring occasionally.
6. 6Bring the mixture slowly to a boil over medium heat, stirring frequently, then continue at a steady boil, stirring often to prevent scorching, relying on the plum skins' natural pectin to help the jam set.
7. 7Cook until the mixture reaches the gel point: 220°F on a candy thermometer (8°F above the boiling point of water at sea level), or until a spoonful mounds and wrinkles when pushed on a chilled plate.
8. 8Remove from the heat and skim off any foam.
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, center a warm lid on each jar, and screw on a band until fingertip tight.
11. 11Process in a boiling-water canner, jars covered by 1 to 2 inches of water, for 10 minutes for half-pints and 15 minutes for pints, timing from when the water returns to a full rolling boil.
12. 12Adjust for altitude: add 5 minutes at 1,001-3,000 feet, 10 minutes at 3,001-6,000 feet, 15 minutes at 6,001-8,000 feet, and 20 minutes above 8,000 feet.
13. 13Turn off the heat, wait 5 minutes, then remove jars to a towel-lined counter and let cool undisturbed for 12 to 24 hours.
14. 14Check each seal (concave, firm lid), remove the bands, wipe the jars, and label with contents and date.
15. 15Store in a cool, dark place up to 1 year for best quality; refrigerate after opening and use within about 3 weeks.
16. 16Do not reduce the sugar or the lemon juice, since this proportion of fruit, sugar, and acid is what keeps the jam safe and helps it set properly.