Gelatine

Powdered and leaf gelatine are both made commercially from pig skin, the latter being the more refined and preferred form, which has the benefit of dissolving immediately without leaving any residue. Soak the leaves in cold water for 5 minutes, then squeeze them dry before adding to the hot liquid you want to set. Nine gelatine leaves will set 600 ml / 1 pt of liquid to a firm jelly. When making stock at home, the cooking extracts gelatine from the bones, which is what causes the stock to jelly or set when cold.