Whole grains are the grains as they are harvested, while pearl barley has had the outer layer removed to reveal a polished white kernel. Whole grains must be softened before being cooked in order to be edible. Soak them in plenty of cold water for at least 2 hours or even overnight. The whole grains are then often combined with meat, and lamb in particular, as in the classic recipe for Scotch broth. The barley thickens this wholesome soup as well as adding flavor and a pleasing nutty texture.
As pearl barley has been well polished to remove the outer husk, the grain cooks more quickly and no prior soaking is necessary. Pearl barley is also used to thicken and enhance the flavor and texture of soups.
** Asian Online Recipes