The noseful of floral aroma, the thirst quenching citrus edge, the bitter finish.
All produced by the flower of the vine
Hops have been widely used in beer for many years, cultivated in Europe since the 8th century, but only appearing in English beers in the 16th. Before which many other plants were used to flavour beers.
o.k here comes the science bit.
The hop cone is made up of interleaved bracts, at the base of each are oil glands. It is this oil which gives bitterness to beers. The oil contains Phenolic alpha acids, such as humulone and beta acids like lumulone.
The alpha acids are isomersied by heating, and produce bitterness in the green beer. The beta acids tend to produce their bitterness over a longer period of time as the beer matures.
The bitterness can be measured using a spectrophotometer to identify the concentration of the acids in the beer. The standard unit is the IBU (international bitterness unit) Nice to see a sensible aconym hey.
The aroma comes from terpenes such as myrcene, humulene and limonene. These produce floral and woody aromas, as well as those lovely citrus notes.
Since these terpenes are volatile, hops are usually added in two stages. The first early on in the boiling of the wort, to extrcat and isomerise the acids, the second towards the end to catch the terpenes.
Some beers are also dry hopped, with hops added to the cask.
At high levels, hops can help to preserve beer but generally they are not used in large enough amounts to stop spoilage of beer though bacterial contamination.