Hops contain hundreds of components, but most of the brewing value of the hops is found in the soft resins, hop oils, and polyphenols.
Hop resins are subdivided into hard- and soft-resins based on their solubility. Hard resins are of little significance, as they contribute nothing to the brewing value, while soft resins (α- and β-acids) contribute to the flavoring and preservative properties of beer. Alpha and beta acids are two compounds present as soft resins and are responsible for bitterness. Alpha acids are responsible for about 90 percent of the in beer. Magnesium, carbonate, and chloride ions can accentuate hop bitterness too.
Although hops with high alpha acid content are preferred for their bittering and flavoring properties, hops are also selected for the character of their oils that contribute to aroma. Essential oils are the principal aroma components of hops. Dependent on variety, hops contain from about 0.4 to 2.5 mL/100 g of steam volatile, essential oils (Taylor, 2006). Oils are largely responsible for the characteristic aroma and tastes (e.g., floral, spicy, citrus, and estery) 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.
Hops contain a number of phenolic components and derivatives of low molecular mass, such as phenolic acids, coloring components, and polycondensated substances with strong tanning properties. Hop polyphenols play a role in the establishment of the intrinsic colloidal stability of beer. Most of the hop polyphenols are removed during wort boiling by precipitation with proteins improving the colloidal stability of beer. The amount and influence of hop polyphenols can be significantly affected by choice of hop product, because, in some products, polyphenols may be reduced or removed completely.
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