Add berries, lemon juice, and sugar to a large pot and heat to medium. Use a fork or a potato masher to gently mash down the berries to release some of their jucies.
Heat on medium, bring to a gentle boil, and then turn the heat down to medium-low to simmer. The berries will foam, just stir occasionally to reduce the foam.
Let simmer until the jam begins to gel, or when the temperature of the jam reaches 221° F.
Add to canning jars and can with a water bath or store in fridge or freezer.
