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Reproducibility Trials in a Research Brewery and Effects on the Evaluation of Hop Substances in Beer - Part 3: Transfer Rates of Aroma Compounds from Hops to Beer and their Ageing Behaviour
A. Gahr, A. Forster, J. De Clippeleer and F. Van Opstaele

The reproducibility aspect of fresh and moderately aged late and dry hopped beers was previously reported in the papers part 1 [1] and part 2 [2] respectively. The present paper (part 3) focuses on the transfer of several compounds from hops to beer and their behaviour during beer ageing at different temperatures for 470 days. Transfer rates were found to be different for the examined substance groups and whether the hops were applied in the brewhouse (late) or during maturation (dry hopped): mono- and sesquiterpene hydrocarbons <1 % in late hopped beers, up to 2% in dry hopped beers; esters: 20 to 40% in late hopped beers, 40-80% in dry hopped beers; linalool: 60% in late hopped beers, 80% in dry hopped beers; sesquiterpene alcohols: 7-18% in late hopped beers, 10-50% in dry hopped beers. A late and a dry hopped beer were aged for 470 days at 0C, 4C, 20C and 30C and analysed for several fermentation by-products, ageing carbonyls and relevant hop aroma compounds. The concentration of acetates and ethyl esters decreased significantly at 20C and 30C, higher alcohols showed good stability. The concentrations of all Strecker degradation products and furfural started to increase at 4C, with pronounced increases at 20C and 30C. Monoterpenes proved to be relatively stable when stored at low temperatures (0 and 4C); however, at 20C and 30C, lost approximately 25% and 50% of their initial concentrations. The hop-derived carboxylic acid esters in the beers decreased by ca. 10% at 0C. The relative losses increased dramatically to 60 to 70% at 20C, and to more than 70% at 30C. Only at 30C there were significant losses of total linalool. By contrast, the concentration of α-terpineol increased. Similar to linalool, a significant decrease of the β-citronellol concentration was observed at 30C. The racemization of the flavour-active R-linalool to the more inactive S-linalool was particularly evident at the higher temperatures.

Descriptors: reproducibility, transfer rates, hop aroma compounds, beer ageing, ageing aldehydes

BrewingScience, 72 (November/December 2019), pp. 217-227