Korbinian Haslbeck
Research Center Weihenstephan for Brewing and Food Quality, TU Munich

RAW MATERIALS & TECHNOLOGIES
Keywords: essential oil, fermentation, dry hopping

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.

Factors that potentially influence amounts of terpenoids during fermentation were investigated. Samples of industrially produced all malt wort 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. Uptake of terpenoids by yeast cells was analyzed. The hops, SPE-water extracts and beer samples were analyzed by several chromatographic systems using 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. 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. 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 but produced by yeasts at 1.2–2.6 µg/L.

This work provides insights regarding biochemical and chemical-physical processes during fermentation influencing flavor and levels of hop essential oil constituents in final beer.