6 cups blueberries
3½ cups sugar
1 vanilla bean
½ teaspoon butter
4 tablespoons lemon juice
2 teaspoons lemon zest
- Keep it Sterile.
Wash 4 small jars and then sterilize in simmering water for at least 15 minutes. Let rest on a clean, dry towel. Keep the bands and lids in hot water, but do not allow the water to boil. Place a plate in freezer for later use.
- Be Picky.
Rinse berries and remove any stems or spoiled fruit. Use potato masher to smash half of fruit then combine fruit with sugar, vanilla bean, butter, lemon juice and zest in large, non-reactive pot such as stainless steel or enameled cast-iron.
- Get Cooking.
Cook fruit mixture on medium until sugar dissolves, then increase heat and cook to gel point, approximately 20-30 minutes. Berries begin to look glossy when gel point is reached.
- Test it Out.
Test for gel point by placing 1 teaspoon of jam on the chilled plate. Once jam has cooled, surface should wrinkle when pressed with your finger. If it does not wrinkle, continue cooking and test again.
- Fill ‘Em Up.
Ladle jam into jars with wide-mouthed funnel. Leave ¼-inch between rim of jar and jam to insure proper seal. Stir jam with chopstick to remove air bubbles. Wipe rims of jars with clean paper towel and place bands and lids on jars. Do not over-tighten bands.
- Process Away.
Place jars in a large pot of boiling water over high heat and cover with lid. Keep water level at least 1 inch over top of jars. After water returns to boil, process for 15 minutes; adjusting time based on altitude. Remove from water and place on towel. Let rest for 24 hours.
Adjustments for increased altitude
Increase Processing Time is Required for Higher Altitudes