Rock sugar

Not a sugar used as an ingredient, this is a decorative product named for its porous, rough, rocklike appearance. Rock sugar is made by adding royal icing to a sugar syrup cooked to 285°F(141°C). This causes the syrup to turn opaque and bubble up in the pan. The eruption (swelling) and recrystallization occur as a reaction to quickly beating the egg white and sugar in the icing into the hot syrup. The mixture is then poured into a large bowl, where it continues to foam and expand; eventually, it hardens.