Stability of hop beta acids and their decomposition products during natural ageing

• Published in: Acta horticulturae no. 1010; pp. 221 - 230
• Main Authors: Krofta, K, Vrabcová, S, Mikyska, A, Jurková, M, Cajka, T, Hajslová, J
• Format: Journal Article
• Language: English
• Published: International Society for Horticultural Science 01.01.2013
• Subjects: air; alpha acids; beers; beta acids; bitterness; boiling; brewing; hops; leaves; oxidation; temperature
• ISSN: 0567-7572
• DOI: 10.17660/ActaHortic.2013.1010.26

Instability and tendency to oxidation depending to conditions is a dominant property of hop beta acids. Mentioned property has an impact both on hop storage and beer brewing process. Approximately half amount decomposes at room temperature under open air conditions in the course of one month. After 6 months the rate of degradation is more than 90%. Dynamics of decomposition is much slower in leaf hops, primarily during first 6 months of storage. Beers hopped by partially oxidized beta acids showed perceptible sensorial bitterness. Bitterness was pleasant and not clinging. Changes of beta acids in the course of ageing explain that bittering potential of old hops does not declines proportionally to alpha acid loss. A large share of degradation products are formed by cyclization of prenyl side chains of beta acids as arises from mass spectra analysis (tricyclolupulones and hydroxytricyclolupulones). Comparison of decomposition products mass spectra emerging during natural ageing and laboratory wort boiling shows discovery of several unpair fragments beside of many identical ones. It indicates that decomposition products of beta acids established during natural ageing and wort boiling process are not fully idetical.