How to Make Blackberry Jam Using a Water-Canner
4 cups crushed blackberries (about 2 quart boxes blackberries)
7 cups sugar
1 pouch liquid pectin
Yield: About 8 or 9 half-pint jars
To Prepare Fruit
Sort and wash fully ripe berries; remove any stems and caps. Crush berries and extract juice.
To Make Jam
Measure crushed blackberries into a kettle. Add sugar and stir well. Place on high heat and, stirring constantly, bring quickly to a full boil with bubbles over the entire surface. Boil hard for 1 minute, stirring constantly. Remove from heat and stir in pectin. Skim.
Fill hot jam immediately into hot, sterile jars, leaving ¼ inch headspace. Wipe rims of jars with a dampened clean paper towel; adjust two-piece metal canning lids. Process in a Boiling Water Canner.
Recommended processing time for hot packs in a boiling water canner for half-pint and pint sized jars
0 - 1,000 ft - 5 min
1,001 - 6,000 ft - 10 min
Above 6,000 ft - 15 min