Prep 3 pint or 6 half pint jars.

Combine mashed berries, sugar, lemon zest and juice in a large pot (a wide, non-reactive pot is best). Bring to a boil, stirring regularly. Skim the foam that develops.

When the jam has thickened a bit* and the boil can’t be stirred down, sprinkle in the pectin and stir to combine. Cook for an additional 5-8 minutes, until the jam seems quite thick (the saucer test is helpful here).

When the jam has thickened to your liking, remove it from the heat. Ladle into jars, wipe rims, apply lids and process in a boiling water canner for ten minutes. When time is up, remove jars from canner and let cool on a folded kitchen towel.

When jars are cool enough to touch, remove rings and test seals. Jam is ready to eat as soon as it is cooled but can also be stored in a cool, dark place for up to a year.