Blackberry

Blackberry is a dark cane berry. For preserving, ripeness is the pectin fork. Ohio State: sour blackberries, if not overripe, have enough natural pectin and acid to gel with added sugar only; ripe blackberries sit in the group that is low in acid or pectin and might need addition of either ¹. Taste the berry before you assume the kettle will set.

Jam identity. 21 CFR 150.160 lists blackberry (other than dewberry) in Group I ². That is a labeling fruit, not a process time. See Jam and Pectin.

Ohio’s no-added-pectin jelly table includes blackberries; their jam-without-pectin berry row lumps blackberries with raspberries and strawberries ¹. Those charts are quantity starting points, not a canned-jam license. Raspberry is the sibling cane berry; Strawberry is the soft neighbor that always needs help.

What to notice. Sour, seedy, stained fingers. Overripe collapse is a Group II problem. Do not invent a water-bath time.