Mixed Berry Jam

From the garden

• 2½ lb mixed ripe berries (blackberries, raspberries, mulberries, serviceberries), picked over and rinsed — to yield 5 cups crushed; any mix works

From the pantry

• 7 cups granulated sugar — measured out in advance; the full amount is required for the set
• 1¾ oz powdered fruit pectin — one standard box
• 2 tbsp bottled lemon juice — not optional — sweet berries like mulberries and serviceberries are low-acid and need it for safe water-bath canning

1. Fill a boiling-water canner and bring it to a simmer. Wash 8 half-pint jars and keep them hot in simmering water; prepare the lids per the manufacturer's directions. Measure the sugar into a bowl.
2. Crush the berries one layer at a time with a potato masher — you want broken fruit, not purée. Measure exactly 5 cups crushed berries into a tall, heavy pot and stir in the lemon juice and pectin.
3. Bring to a full rolling boil over high heat, stirring constantly. Add all the sugar at once, return to a rolling boil that stirring can't knock down, and boil hard exactly 1 minute. Off the heat, skim any foam.
4. Ladle the hot jam into the hot jars, leaving 1/4 inch of headspace. Wipe the rims clean and screw on the lids to fingertip-tight.
5. Process in the boiling-water bath, covered by 1–2 inches of water, for 10 minutes at a steady boil. Altitude adjustment: add 5 minutes at 1,001–6,000 feet, 10 minutes above 6,000 feet. Rest 5 minutes off the heat, then lift the jars out.
6. Cool undisturbed 12–24 hours, check that the lids sealed concave, remove the bands, and label. Refrigerate any jar that didn't seal and use it first.