Rye berries are whole grain rye with the hull removed. They can be cooked similarly to wheat berries for use in sides, soups, pilaf, breakfast cereals or grain salads. You can also grind them into homemade whole grain rye flour.
Rye (Secale cereale) was the principle bread-making grain of Northern Europe for centuries (either by itself or blended with wheat) before being largely replaced with modern wheat. It has a mild, nutty, walnut-esque flavor, and the whole grains (berries) have a firm, chewy texture once cooked.
While rye has faded into the background in much of northern Europe, it still remains important in traditional breads in Germany (pumpernickel), Russia (traditional black bread), and some countries in central & eastern Europe, where the colder climate is better suited to rye cultivation than wheat.
Rye remains a niche grain in the US & Canada, but continues to play an important role in some ethnic breads (like Jewish rye) and the production of rye whiskey.
While rye naturally contains less gluten than wheat, it is not a gluten free grain.