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On the Fate of β-Myrcene during Fermentation The Role of Stripping and Uptake of Hop Oil Components by Brewers Yeast in Dry-Hopped Wort and Beer
K. Haslbeck, S. Bub, C. Schnberger, M. Zarnkow, F. Jacob and M. Coelhan

Hops play a significant role in determining the aroma of beer. The essential oil of hops contains a large number of flavor-active components. Concentrations of essential oil constituents in beer depend on factors such as the time of hop addition in the brewing process and hop amount added. Generally, compound classes such as mono- and sesquiterpenes do not reach the threshold concentrations in the final product, but in dry-hopped beers after main fermentation they often do. Two factors that potentially cause decreased amounts of terpenoids in beer were investigated. In case of the non-polar compound β-myrcene, losses due to releases into the gas phase during standardized laboratory-scale fermentations were studied. Samples of industrially produced all malt wort (11.5P) were dry-hopped at pitching with Mosaic hops. Two yeast strains that are widespread in German beer production were used in trials, TUM 68 (S. cerevisiae) and TUM 34/70 (S. pastorianus). A method for dissolving fermentation gases in bubbling water columns was used. The hops, SPE-water extracts and beer samples were analyzed by several chromatographic systems using two different GC-FID, nanoLC-MS/MS, GC-MS and HS-GC-MS, respectively. Tendency was shown that higher temperatures at primary fermentation cause increased releases of aroma compounds into the gas phase, which was observed on model fermentations in previous studies. The reversible uptake of β-myrcene by yeast cells, identified in separate test series, was determined as being a highly effective factor decreasing amounts in beer systems. In bottled beers 100 million cells/ml led to decreased amounts of about 9899%. It was shown that solvent systems with similar properties to beers (5% and 10% ethanolic solution) are inadequate for re-dissolving compounds attached to yeasts. The absorbed amount in yeast therefore cannot contribute to the flavor of beer. Incomplete recovered amounts of β-myrcene even in pure ethanol suspensions indicate that there are strong bonds between yeast cells and the odor compound. Linalool, on the other hand, was not affected by the test conditions used.

Descriptors: S. cerevisiae and S. pastorianus, Humulus lupus L., dry hopping, fermentation, beer flavor, β-myrcene and linalool

BrewingScience, 70 (November/December 2017), pp. 159-169