Advanced hop chemistry in connection with beer flavour.

Kuroiwa, Y., Kokubo, E. and Hashimoto, N.

Abstract
The main contribution to the bitter flavour of beer is from compounds of the isohumulone and allo isohumulone group, of which, allowing for stereoisomers, there may be 900 components. The bitter flavour of beer from freshly harvested hops is almost exclusively derived from this group of substances. With hops which have deteriorated by kilning and storage the decomposition products of lupulones and humulones contribute to the bitter flavour. The lupoxes a, b and c and lupdoxes a and b from the oxidation of lupulones are all of greater bittering power than the original lupulone and contribute significantly to the bitter flavour of beer brewed with old hops. The hoppy aroma of beer is not due to the essential oil of hops which is evaporated in boiling the wort but to water soluble decomposition products from the hop oil and resins. Of these the most prominent are 2 methyl 3 buten 2 ol, mostly from lupulone and 2,4 hexadien l al from humulones together with beta caryophyllene from hop oil. The last is largely absorbed by the yeast during fermentation so the hoppy aroma of beer is mostly due to decomposition products from the hop resins.
Keywords: aroma beer bitter substances chemistry chromatography constituent flavour gas hops oil