Irish moss, or carrageen, is an edible red seaweed (Chondrus crispus) gathered from the cold rocky shores of the North Atlantic. Boiled in milk it releases a natural gelling polysaccharide that sets into a soft pudding, and it is the original commercial source of carrageenan, the seaweed gum (E407) used to thicken and stabilise ice cream, dairy drinks and countless processed foods.