The principle cereal grain used in brewing. Two species, Hordeum vulgare and Hordeum distichon are most commonly grown and many varieties exist some of which are planted in the spring others in the winter. The grains of barley are quite large and contain high levels of starch and also of digestive enzymes. Two row barleys are larger than six or four row barleys due to the selection of two rows of grains down the stem rather than the wild type six rows.