Cluster (Hop) is one of the oldest US hops grown in North America. It is considered to be a bittering hop with modest levels of alpha-acids (5%–9% w/w) and low oil content (0.4–0.8 ml/100 g). The rootstock’s origin is not known for certain; however, it is believed to have originated from a chance (open) pollination of the English Black Cluster with an American wild male, probably on the east coast of the United States sometime in the late 18th century. There are four different USDA accession numbers for this variety: Yakima Cluster (also termed L-1)–USDA 65102, Late Cluster L-16–USDA 21011, Late Cluster L-8–USDA 65104, and Early Cluster–USDA 65103. They are all very similar with the primary difference being the time of ripening. All Clusters are very susceptible to downy mildew and therefore cannot be grown successfully in the Willamette Valley of Oregon. They do well in the Yakima Valley, Washington, and Treasure Valley, Idaho. All have excellent vigor and high production potential. The storage stability of Cluster’s alpha acids is among the best of all hops in the world and it keeps very well even in non- refrigerated storage. Cluster acreage has declined significantly from nearly 90% of total US hop production in the 1970s to about 1.25% (501 acres with 1.19 million lb production) in 2009. Cluster is often described as having a clean bitterness and a blackcurrant-like aroma. At one time, the vast majority of American beer contained Cluster, but Galena has supplanted it as the most widely grown American hop variety.