Rinse and mash berries. Place in a 6-quart or larger pot with sugar
and slowly bring to a boil, stirring to dissolve sugar. Boil for
20 to 30 minutes, stirring frequently to prevent sticking and scorching,
until thickened. Jam will thicken as it cools.
Add lemon juice at the end of cooking time.
Remove from heat and skim off foam with a spoon. Ladle jam into
clean, hot jars, leaving 1/2-inch headspace; seal.