For five thousand years or more hops has been used medically and as a flavoring agent and preservative in beer. Pliny the Elder made one of the earliest known references to hops (61-113 A.D.) The cultivation of hops in Germany was documented as early as the eighth century and likely occurred before that in other parts of Europe.
Documented use of hops in beer making was recorded in the twelfth century. Commercial hops production began in England in the 1500's. A variety of hops was brought to America from England in 1629, but native varieties existed here. In the early 19th century hops production and trade was established in New England and New York and thrived for a relatively short time period (decades). As better growing conditions were discovered with America's migration West, eastern hops operations declined or lapsed altogether.
By the early 20th century hops production was well established in California and the Pacific Northwest. Washington, Oregon, and Idaho continue to this day to lead American hops production.
A certain natural selection lent itself to hops becoming a dominant flavoring for beer. Historically, many botanical ingredients have been used in beer making. Over time, hops stood out not only for its flavor profile but also as a matter of practicality. Hops, it turns out, wards off specific strains of bacteria that can be responsible for spoilage and off flavors.
Hops' antibacterial properties provided flavor protection during fermentation and extended the shelf life of the finished product as well. Beer brewed and preserved with hops could be transported over distance, thus expanding beers' commercial potential. This is truly an example of form following function, something any good engineer can appreciate!
The compound in hops that lends its flavor protecting qualities is an oily alpha acid called humulone. It has been determined that humulone has antimicrobial, antiviral, and antibacterial qualities Indeed, IPA (India Pale Ale), a heavily hopped malt beverage was so named because it was brewed extra strong, then transported from Brittian to India where it could be diluted to a more palatable strength. The heavy concentration of hops in IPA, not to mention its alcohol content, allowed for transport over long distances and time spans.
Dry Hopping - refers to the addition of hops to your wort for aroma; after the wort has cooled and/or while fermentation has begun. May also imply the use of whole cone hops.
Wet Hopping - similar to dry hopping - may imply an addition of hops later than dry hopping such as after primary fermentation has completed . May also imply the use of fresh as opposed to dried cones.
Pellet - hops flowers that have been kiln dried, pulverized and extruded into a form that resembles rabbit pellets. It is a means of preserving hops cones, making them more compact, easier to use and easier to measure. It is the most common form of hops used in home brewing today.
Whole Cone - hops flowers left intact - as opposed to being pelletized. Synonymous with 'Leaf Hops'
Leaf Hops - hops flowers left intact - as opposed to being pelletized. Synonymous with 'Whole Cone'
Alpha Acid - an oily compound found in mature female hops flowers, specifically humulone, responsible for its bittering and preservative qualities. The degree of bittering provided by a particular variety of hops is expressed in its percentage of alpha acid. Hops varieties higher in alpha acid will have a greater potential to lend bittering to your beer recipe (brew).
Any hops product will be labeled with an alpha acid percentage usually expressed as a range. It represents the amount of alpha acid as a percentage of its total weight. As you would expect with any agricultural commodity, actual alpha acid percentages for a given variety will vary based on growing conditions, processing, preservation, etc.
Isomerize - the process by which a molecule is transformed by a rearrangement of its atoms. Hops is said to 'isomerize' when the heat of the boil transforms its alpha acid compounds into iso-alpha acids and thus bitter flavor.
Bittering Hops - hops added early in the boil (as opposed to flavor/aroma hops added late). Flavors and aromas distinct to the variety of the hops you are using will dissipate in the boil, leaving behind mostly the bittering quality. Note that without hops, many beers would taste sweet due to undigested sugars that remain after fermentation. One of the reasons hops became a staple beer flavoring was to balance a beer's sweetness.
Flavor/Aroma Hops - hops added late in the boil (as opposed to bittering hops added early). While a long boil will cook off hops flavor and aroma compounds, late addition hops will retain flavors and aromas. Generally, flavor hops are added with 10 minutes of remaining boil time and aroma hops are added with 5 minutes of remaining boil time.
IBU - International Bittering Units - A quantitative measure of the amount of iso-alpha acids (or bitterness) of a given beer.
Noble Hops - of European origin and often still more commonly associated with European beer production and recipes such as pale lagers. These hops are generally lower in bitterness and higher in flavor. The main varieties of noble hops are Hallertauer, Tettnanger, Spalter, and Saaz.