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Hops
Hop Constituents
Hops contain hundreds of components, but of particular interest are resins, oils, and polyphenols.
Hop Resins
Hop resins are subdivided into hard and soft, based on their solubility. Hard resins are of little significance, as they contribute nothing to the brewing value, while soft resins contribute to the flavoring and preservative properties of beer. Alpha and beta acids are two compounds present in the soft resins and are responsible for bitterness. Alpha acids are responsible for about 90% of the bitterness in beer. Magnesium, carbonate, and chloride ions also can accentuate hop bitterness.
Alpha Acids: Alpha acids are the precursors of beer bitterness since they are converted into iso-alpha acids in the brew kettle. The three major components of alpha acids are humulone, cohumulone, and adhumulone.
BetaAcids: Hops also contain a second group of acids known as the beta acids. The beta acids (lupulone, colupulone, and adlupulone) are only marginally bitter.
Hop Oils
Although hops that have high alpha acid content are preferred for their bittering and flavoring properties, hops are also selected for the character of their oils. Oils are largely responsible for the characteristic aroma of hops and, either directly or indirectly, for the overall perception of hop flavors. Hops selected for character of their oil content are often referred to as aroma or "noble" type hops. Oils also tend to make a beer’s bitterness a little more pronounced and to enhance the body or mouth feel of the beer.
Hop Polyphenols
Polyphenols found in hops include the anthocyanogens, tannins, and catechins. Some polyphenols act as antioxidants, protecting beer against oxidation, while others contribute to beer color and haze formation. Polyphhenols may also cause an unpleasant astringency. Significant proportions are removed during boiling by precipitation with proteins.
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