Plants

Beer is more often then not made up of a flower called hops. Hops flavour the beer and are used as a stabality agent. Hops is also sometimes used in herbal medicine. Hops is used in beer for many reasons; the flower gives it a bitterness that helps it to balance the sweetness of the malt that is in it, it gives beer a special aroma that makes it appealing, and it holds an antibiotic effect that helps with the activity of the yeast in the beer.

While hop plants are grown by farmers all around the world in many different varieties, there is no major commercial use for hops other than in beer, although hops are an ingredient in Julmust, a carbonated beverage similar to cola soda that is popular in Sweden during December. 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 favour the exclusive activity of brewing yeast in the fermentation of beer. Beta acids do not isomerise during the boil of wort, and have a negligible effect on beer flavour. 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-flavours of rotten vegetables or cooked corn.

The flavour imparted by hops varies by type 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 wort has cooled and the beer has fermented is known as “dry hopping”, and adds hop aroma, but no 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. Flavours and aromas are described appreciatively using terms which include “grassy”, “floral”, “citrus”, “spicy”, and “earthy”. 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, or IPA) can have high levels of bitterness.