Tomato Jam Canning Instructions 1. Sterilize canning jars. 2. Pour hot jam into hot, sterile jars, leaving ¼-inch headspace. 3. Wipe rims of jars with a dampened clean paper towel; adjust two-piece metal canning lids. 4. Process 15 minutes in a boiling water bath. Adjust for altitude above 1000 ft. 5. Remove from water bath and cool completely before storing in a cool place.