Classic Strawberry Jam (for canning)

May 25, 2016
From the book Foolproof Preserving from America's Test Kitchen
Classic Strawberry Jam (for canning) | WGBH | CRAVING BOSTON

Strawberry jam is a universal favorite. Naturally low in pectin, strawberries are often cooked too long, causing the fruit to lose its bright flavor. We shortened the cooking time by cutting the strawberries into smaller pieces and then mashing them to release their juices and jump-start the cooking process. Shredded apple added natural pectin and fresh flavor to the mix. Lemon juice added acidity to balance the sugar’s sweetness and helped the natural pectin to gel. Small, fragrant berries produce the best jam. For safety reasons, be sure to use bottled lemon juice, not fresh-squeezed juice, in this recipe.

Ingredients 
3 pounds pounds strawberries, hulled and cut into 1/2-inch pieces (10 cups)
3 cups sugar
1 1/4 cups peeled and shredded Granny Smith apple (1 large apple)
2 tablespoons bottled lemon juice
Notes 

Do not try to make a double batch of this jam in a large pot; it will not work. Rather, make two single batches in separate pots.

Directions 

1. Place 2 small plates in freezer to chill. Set canning rack in large pot, place four 1-cup jars in rack, and add water to cover by 1 inch. Bring to simmer over medium heat, then turn off heat and cover to keep hot.

2. In Dutch oven, crush strawberries with potato masher until fruit is mostly broken down. Stir in sugar, apple, and lemon juice and bring to boil, stirring often, over medium-high heat. Once sugar is completely dissolved, boil mixture, stirring and adjusting heat as needed, until thickened and registers 217 to 220 degrees, 20 to 25 minutes. (Temperature will be lower at higher elevations.) Remove pot from heat.

3. To test consistency, place 1 teaspoon jam on chilled plate and freeze for 2 minutes. Drag your finger through jam on plate; jam has correct consistency when your finger leaves distinct trail. If runny, return pot to heat and simmer for 1 to 3 minutes longer before retesting. Skim any foam from surface of jam using spoon.

4. Place dish towel flat on counter. Using jar lifter, remove jars from pot, draining water back into pot. Place jars upside down on towel and let dry for 1 minute. Using funnel and ladle, portion hot jam into hot jars, leaving 1/4 inch headspace. Slide wooden skewer along inside edge of jar and drag upward to remove air bubbles.

5a. For short-term storage: Let jam cool to room temperature, cover, and refrigerate until jam is set, 12 to 24 hours. (Jam can be refrigerated for up to 2 months.)

5b. For long-term storage: While jars are hot, wipe rims clean, add lids, and screw on rings until fingertip-tight; do not overtighten. Return pot of water with canning rack to boil. Lower jars into water, cover, bring water back to boil, then start timer. Cooking time will depend on your altitude: Boil 10 minutes for up to 1,000 feet, 15 minutes for 1,001 to 3,000 feet, 20 minutes for 3,001 to 6,000 feet, or 25 minutes for 6,001 to 8,000 feet. Turn off heat and let jars sit in pot for 5 minutes. Remove jars from pot and let cool for 24 hours. Remove rings, check seal, and clean rims. (Sealed jars can be stored for up to 1 year.)