Hops (Humulus lupulus) are clusters of blossoms of a perennial herbaceous vine belonging to the hemp family. The stems and tendrils may extend up to nine meters in length and when cultivated are trained onto trellises for easier harvesting. Hops are primarily a flavoring agent for beer, imparting a bitter flavor and characteristic aroma. They also promote clarification of the beer and have foam-improving properties. Hops may also have antiseptic properties, retarding bacterial growth that can spoil beer. During the brewing process, the "wort" or liquid obtained after "mashing" the malted barley is boiled with hops. This process not only infuses the liquid with various resins, volatile oils, and flavor compounds, but also helps clarify the beer by coagulating unwanted substances that cloud the liquid. This coagulated mass ("hot trub" or "break") is removed from the "wort."
The U. S. Department of Agriculture produced (and continues to produce) a wealth of agricultural publications, including the Farmers' Bulletin series. No. 304 (1922) is a revised edition of the 1910 publication, Growing and Curing Hops. USDA publications are easily found using the National Agricultural Library's databases, including Agricola.
Source: Stockberger, W. W. Growing and Curing Hops, (Farmers' Bulletin No. 304), U. S. Department of Agriculture: Washington, D.C., 1907. Crerar S21.A6 no.304
Fries, Martin. Anleitung zum Hopfenbau an Stangen und Drahtgerüsten. Das Trocknen auf Trockenböden, Rahmen und mittelst Feuerung, 2nd ed., Der Fervasser, Stuttgart, 1882. Crerar 633.241 O200