This article was previously posted on the Examiner as part of my Science of Beer series.

This is part two of a multi-part article on the science behind making beer.

Beer is composed of only four ingredients: water, barley, hops, and yeast. Hops are the one ingredient that most people know the least of. Why are they added to beer? What is their purpose?

Hop plants are part of the hemp family Cannabinaceae. The Cannabinaceae family then breaks down into two genera: Cannabis, from which hemp fibers and marijuana come from, and Humulus. The Humulus genus is where hops come from. The Humulus genus breaks down into three different species, two of which are different Asian hop varieties and then there is Humulus lupulus, which containes the European and American hop varieties that are typically used in beer production.

Hop plants grow as a bine, similar to a vine however its method of climbing and attaching itself is different. The female hop plants create a flower cluster called a seed cone. This cone is similar in shape and purpose to other plant cones, like pine cones. However hop cones are green, soft and very leafy as opposed to the rigidness of the pine cone. These cones are the parts of the plant that are plucked and used in beer.

When brewing beer, malted barley is mashed in hot water to extract the sugars. The sugar water, called wort, is then drained where it moves to the next part of the process, the boil. Wort is boiled for about an hour for the purpose of both sanitizing it, and to boil off some of the water leaving the sugar concentration higher. It is during this boil that hops are added as well.

Hops serve three different purposes in beer: adding bitterness to balance out the sweetness in the wort, adding a pleasant aroma to the beer, and to prevent spoilage.

Hops contain an internal resin that contains both alpha and beta acids. Alpha acids contribute bitterness and beta acids contribute aroma. Thus the varieties of hops that contain high levels of alpha acids are called bittering hops and the varieties that contain higher levels of beta acids are called aroma hops. Bittering hops are added earlier in the boil because the alpha acids need heat to break down and be released. The earlier in the boil they are added, the more heat is added and thus the higher level of bitterness is added to the wort. Beta acids, on the otherhand, do not need heat to be released so aroma hops are added at the very end of the boil or even during the fermentation process. Adding hops during fermentation is called dry-hopping and is done regularly in many ale styles. Adding aroma hops during the end of the boil or during fermentation adds only more hop aroma without adding additional bitterness.

Lastly, hops help to prevent spoilage in beer. The alpha acids have a natural antibiotic and antibacterial quality to them. Prior to beer production, hops were used as a form of medicine because of these qualities. The antibacterialness of hops was realized when Britian began trading with India. Beer was produced and brought aboard ships for the sailers to drink during the voyage to India. By the end of the trip, most of the beer had been spoiled. However the beers that had hops used instead of other bittering herbs were not spoiled since any bacteria it came in contact with were killed by the alpha acids in the hops. Thus more hops were added to beer to ensure it would would not spoil during the trip to India; and with that the IPA, or India Pale Ale style was born!

Once the boil is complete and hops are added, the wort is then chilled and yeast is added to ferment. Yeast and fermentation will be discussed in a future article.