Hops provide bitterness to balance the sweetness of Malt when making beer, adds flavoring oils and aromas, and also helps to stabilize and preserve beer. Hops used in brewing comes from the flowers of a plant called Humulus Lupulus. The hop plant is a perrenial spiraling vine that requires most soil. The flowers of the hops, called cones are dried before use. These flowers are usually green in color with yellow lupulin glands between the petals that provide many of the oils.
Types of Hops
- Loose or Leaf Hops - Hops in its most natural form. Leaf hops float, provide a nice filter bed when siphoning, and are excellent when fresh. Unfortunately these hops are also most susceptible to exposure to air and oxidization, which means their quality will decline more rapidly unless vacuum sealed in a oxygen barrier bag.
- Plug Hops - Dried and compressed hop cones. When hydrated these are essentially the same as whole hops, but will store better.
- Pellet Hops - Perhaps the most widely available to the home brewer, these hops are dried, chopped and compressed into tiny pellets. They store well, and are easy to measure in small quantities. The chopping and compressing can release some of the lupulin glands to burst losing some aromatic oils.
Hop bitterness is measured in International Bitterness Units' or IBU's. One IBU is one part per million of isohumulone which is a bittering (alpha) acid. IBU's can be estimated when brewing a beer by several different formulas, the most popular of which are the Tinseth, Rager and Garetz formulas. IBU's for light beers are generally in the 10-20 range, while dark flavorful beers such as stouts may have an IBU as high as 50. Some barley wines have IBU values of 100 or more to offset the extreme malty sweetness of the beer. See the Beer Styles BJCP guide for some typical IBU ranges for different styles of beer.
Bittiness in beer is provided by oils released by the hops. The bittering oils of the hops are isomerized (rearranged) during the boil. Insoluable alpha acids (α-acids) are isomerized by the boil into more soluble and stable alpha acids. These alpha acids provide the majority of the bitterness in finished beer. A second component called beta acid also provides some bitterness. Additional compounds in hops provide both aroma and preservative qualities.
The alpha and beta acids in hops are both vulnerable to oxidation which will decrease their effectiveness. Hops will degrade faster at temperatures above freezing. Hops should be refrigerated in your freezer, and sealed in an airtight container (ideally vacuum packed foil oxygen barrier container) to prevent oxidation.