The cones contain a soft resin called alpha acid that gives beer its bitterness flavor. Hops also help to inhibit the growth of certain beer spoiling bacteria, to maintain flavor stability, and to retain the head of the beer. There are many different varieties of hops. They are selected from the rest for their unique bitterness in flavor or aroma. Hops are broadly classified into two groups.
Noble hops are low in bitterness and have a pleasant aroma and flavor.
High-alpha hops have high bitterness but a less pleasant aroma. The high-alpha hops can be used more economically due to the less amount required. However, the flavor of the beer is slightly sacrificed. Years ago, the recipes for beer would call for hops measured in ounces. Since the bitterness for each type of hop was not accounted, the beer's flavor was inconsistent from batch to batch.