The Oxford Companion to Beer

Gas chromatography has helped researchers to identify more than 250 essential oil components. Of these, 22 have been reported to affect hop aroma, and they have been divided into groups: humulene and caryophyllene oxidation products, floral-estery compounds, and citrus-piney compounds. It is these 22 that constitute the HACP (see table).

beer gods. Benjamin Franklin supposedly once said, “Beer is our best proof that God loves us and wants us to be happy.”

Benjamin Franklin supposedly once said, “Beer is our

beer clean is a term that refers to the cleanliness of a vessel used for drinking beer, generally made of glass. Beer clean glassware is critical for the proper presentation and consumption of beer.

Flavor changes are readily noted as the general characteristic sometimes termed “yeast bite.” This is generally a sharp, bitter taste with a meaty and sulphury edge caused by some of the amino acids and nucleotides present in yeast. I

Oxidation of hops leads to cleavage of this side group and the production of 2-methylbutryic acid, which has a distinctive, pungent odor similar to Roquefort cheese. This is why oxidized hops are often described as “cheesy.”

oxygen. Through a series of very complex chemical processes, oxygen reacts with many of the aroma and flavor active compounds in the beer, gradually replacing the fresh and desirable flavors with cardboard-like, papery, and stale flavors.

chemical modifications (reduction processes) of CO2 hop extracts. When used, primarily for industrial lager beer, these are added to finished beer just before packaging and offer the brewer several advantages: avoidance of skunky (lightstruck) flavors that might otherwise form in non-protective clear or emerald glass bottle (See LIGHTSTRUCK), a smooth and easily controlled

maturation of beer.

If present in amounts above the perception threshold, acetic acid conveys a sour vinegar taste and aroma to beer.

If the yeast is not sufficiently active, either because it is not healthy or because the fermentation temperature is too low, too much acetaldehyde may remain in the beer. Bacterial infections can also interfere with yeast fermentation, leaving elevated levels of acetaldehyde in beer.