The use of hops in beer brewing is mainly based on its content of bitter acids and aroma compounds. Due to the loss of volatile odorants during wort boiling, the so-called dry hopping is a possibility to intensify the hoppy aroma in the final beer. To clarify the potential of different hop varieties for aroma modulation of beer via dry hopping, key aroma compounds of three different hop varieties were characterized using the sensomics approach. Aroma extract dilution analysis revealed 41 aroma-active compounds, of which 39 were identified via gas chromatography-olfactometry and gas chromatography-mass spectrometry. The highest flavor dilution factor was determined for myrcene with a geranium-like odor. Fourteen substances were quantitated by stable isotope dilution analysis and further two odorants via the internal standard method; all of them revealed odor activity values (OAVs; ratio of concentration to odor threshold) ≥1. Linalool, 3-methylbutanoic acid, myrcene, and dimethyl trisulfide showed the highest OAVs (>1000) in all analyzed hop varieties. For validation of the analytical data, reconstitution models were prepared by adding all quantitated aroma compounds with OAVs ≥ 1 in their naturally occurring concentrations to cellulose as matrix. All three recombinates showed a very high similarity to the aroma profile of the respective hop sample, confirming the correct identification and quantitation of all key aroma compounds.
There are mainly two options for
the dealcoholization of beer:
evaporation of ethanol by heat treatment, whereby desired aroma-active
compounds are also removed, and stopped fermentation that leads to
beers still containing high amounts of unfermented sugar in parallel
with lower amounts of aroma-active fermentation products. Thus, dry-hopping
could be an opportunity to compensate for these aroma deficiencies.
Therefore, following the sensomics approach, odorants were characterized
in dry-hopped (Hallertauer Mandarina Bavaria, Hallertauer Cascade,
or Hallertauer Mittelfrüh) top- and bottom-fermented alcohol-free
beers either after thermal dealcoholization or stopped fermentation.
Twenty-three odorants were quantitated via stable isotope dilution
analysis, and odor activity values (OAVs; ratio of concentration to
odor threshold) were calculated. Thermally dealcoholized samples showed
high losses (up to 100%) of key odorants like 3-methyl-1-butanol or
3-methylbutyl acetate. During stopped fermentation, aroma compounds
like ethyl butanoate or 2-phenylethanol were formed in relevant concentrations,
leading to OAVs ≥ 1, but the amounts were significantly lower
compared to beers with normal alcohol contents. For hop-derived odorants
(linalool, geraniol, myrcene, and esters), transfer rates between
20 and 90% were found, leading to OAVs ≥ 1 in beer. Furthermore,
hop addition apparently induced the formation of ethyl esters of hop-derived
monocarboxylic acids.
Fruity smelling esters play an important role for the aroma of hops and beer and they have been characterized as key aroma compounds in different hop varieties. Studies on the transfer of hop-derived compounds into beer during dry-hopping showed calculated transfer rates of different ethyl esters far above 100%, leading to the assumption that these esters must be newly formed. To investigate this formation, dry-hopping was imitated in water to eliminate the influence of the beer matrix on the formation of these odorants. Thereby, the formation of ethyl esters of 2-methylbutanoic acid, 3-methylbutanoic acid, and methylpropanoic acid, induced by the addition of hops, was shown. Different approaches inhibiting enzyme activities and experiments with different hop extracts might lead to the assumption that enzymes are involved in the formation of these esters, beside possible transesterification.
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