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Aroma Active Monocarboxylic Acids - Origin and Analytical Characterization in Fresh and Aged Hops
N. Rettberg, S. Thrner, A. B. Labus and L.-A. Garbe

During hop storage secondary metabolites, primarily bitter acids, terpene hydrocarbons and terpenoids, undergo qualitative and quantitative changes. One reaction that influences both - bitter properties and aroma - is the release of extremely flavour active short chain monocarboxylic acids by cleavage of the acyl-side chain of bitter substances. Short chain acids exhibit very intense unpleasant cheesy, sweaty, and rancid smells, however they are key precursors of highly positive flavourings of late hopped beer.

Descriptors: hop aroma, bitter acid degradation, ester formation, mass spectrometry

BrewingScience - Monatsschrift fr Brauwissenschaft, 67 (March/April 2014), pp. 33-47