6 heaping cups Marionberries (or other caneberries, such as blackberries, Loganberries or Boysenberries)
4-1/2 cups sugar
1/3 to 1/2 cup strained fresh lemon juice*
1 tsp butter
Sort fresh Marionberries, removing any leaves or twigs. Rinse them and drain well. Gently stir the berries, the sugar, and the lemon juice together in a bowl, using a rubber spatula; let the mixture stand, stirring gently once or twice, until the sugar has dissolved, about 2 hours (or overnight in the refrigerator).
Wash seven half-pint jars. Keep hot until needed. Prepare lids as manufacturer directs.
Scrape the berry mixture into a large, wide, heavy-bottomed non-aluminum pan. Add the butter and bring the mixture to a boil. Boil rapidly, stirring occasionally at first, and then constantly toward the end, until the mixture reaches the jell point on your thermometer (220 degrees from sea level up to 1,000 feet; 216 degrees at 2,000 feet; 214 degrees at 3,000 feet; 212 degrees at 4,000 feet; 211 degrees at 5,000 feet; 209 degrees at 6,000 feet; 207 degrees at 7,000 feet; 205 degrees at 8,000 feet), which usually takes only about 7 to 10 minutes. Remove from heat.
The butter helps reduce foam, but if some foam remains after you’ve removed the pot from the burner and let the jam settle for about 10 seconds, skim it off.
Ladle hot preserves into one hot jar at a time, leaving 1/4-inch headspace. Wipe jar rim with a clean, damp cloth. Attach lid. Fill and close remaining jars. Jars may be stored in the refrigerator indefinitely (okay, at least for months and months and months), but for storage at room temperature, process the jars in a boiling-water canner for 10 minutes. (At 1,000 to 3,000 feet, process for 15 minutes; at 3,000 to 6,000 feet, for 20 minutes; above 6,000 feet, for 25 minutes).
A fabulous treasure to give away to very special people. Delicious over ice cream, pound cake, or plain as dessert.
Makes 6 to 7 half-pints.
* If the berries seem extremely ripe, use 1/2 cup of lemon juice; if at least one-fifth of the berries seem firm or even slightly underripe, then you can get away with the 1/3 cup of lemon juice.