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Common hop (Humulus lupulus)
The hop (Humulus) is a small genus of flowering plants, native to the temperate Northern Hemisphere. In Poland it grows naturally in dump forest and bushlands, especially along rivers. The female flowers, commonly called hops, are used as flavouring and stabilisers during beer brewing.
Although frequently referred to as the hop vine, it is technically a bine; unlike vines, which use tendrils, suckers, and other appendages for attaching themselves, bines have stout stems with stiff hairs to aid in climbing. It is a perennial herbaceous plant which sends up new shoots in early spring and dies back to the cold-hardy rhizome in autumn. Hop shoots grow very rapidly and at the peak of growth can grow 20-50 cm per week.
The first documented instance of hop cultivation was in 736, in the Hallertau region of present-day Germany, although the first mention of the use of hops in brewing was in 1079. Hops were introduced to British beers in the early 1500s, and hop cultivation began in the United States in 1629.
Hop resins are composed of two main acids: alpha and beta acids. Alpha acids have a mild antibiotic/bacteriostatic effect against Gram-positive bacteria, and favours the exclusive activity of brewing yeast in the fermentation of beer. The flavour imparted by hops varies greatly by variety and use: hops boiled with the beer (known as "bittering hops") produce bitterness, while hops added to beer later impart some degree of "hop flavour" (if during the final 10 minutes of boil) or "hop aroma" (if during the final 3 minutes, or less, of boil) and a lesser degree of bitterness. Adding hops after the boil, a process known as "dry hopping", adds very little bitterness. The degree of bitterness imparted by hops depends on the degree to which otherwise insoluble alpha acids (AAs) are isomerized during the boil, and the impact of a given amount of hops is specified in International Bitterness Units. Unboiled hops are only mildly bitter. Beta acids do not isomerize during the boil of wort, and have a negligible effect on beer flavor. Instead they contribute to beer's bitter aroma, and high beta acid hop varieties are often added at the end of the wort boil for aroma. Beta acids oxidize and oxidized beta acids form sulfur compounds such as DMS (dimethyl-sulfide) that can give beer off-flavors of rotten vegetables or cooked corn.
Particular hop varieties are associated with beer styles. Flavours and aromas are described appreciatively using terms which include "grassy", "floral", "citrus", and "spicy". Most of the common commercial lagers have fairly low hop influence, while true pilseners should have noticeable noble hop aroma and certain ales (particularly the highly-hopped style known as India Pale Ale) can have high levels of bitterness.
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