| Abstract |
- This study examined whether polyphenols contribute a harsh bitterness
to beer, and how polyphenols may otherwise modify beer bitterness in the
presence of iso-a-acids. The experimental portions of this project were
divided into effectively two segments. The first section of the study
encompassed groundwork polyphenol extraction development, and the
examination of the extract in beer in a series of sensory studies. The
polyphenol extract was produced from spent Galena hop material and added
to a low bitterness base-beer at three levels (+0, +100, +200ppm) along with
iso-α-acids from a pre-isomerized Galena hop extract at two levels (+0,
+10ppm) in order to examine the impact on bitterness character by timeintensity
(Tl) and free-choice profiling (FCP) methods, using eleven trained
panelists. Principal Components Analysis of the Tl results showed that the
panelists separated the samples with the higher levels of polyphenols and isoa-
acids from those with lower levels of both based on bitterness duration,
maximum intensity, and area under the curve. Samples 10-100 and 10-200 (+10ppm iso-a-acids and +100 and +200ppm total polyphenols) were
significantly more bitter and had longer duration than the others. A significant
effect was found for both iso-α-acids and polyphenols as well as an interaction
in terms of peak intensity and area under the curve (p<0.001). Similarly, the
results from the FCP easily separated the treatments by bitterness, lingering
bitterness, and astringency. Panelists divided each of the treatments into six
distinct groups based on bitterness intensity, 5 groups based on duration, and
into 2-3 groups based on the remaining consensus descriptors (mouthfeel,
astringency, and bitterness come-up time). Samples high in polyphenols were
frequently given higher intensities for "harsh," "medicinal," and "metallic"
descriptors. The second portion of the experiment involved scaling up the extraction
volumes and solving issues regarding the quality of the extract, which was
then followed by some experimental brews using spent hop material. The
main issues regarding the quality of the extract were the production of haze
and the presence of humulinones (oxidized α-acids), which were present in
the raw materials and have the potential to confound bitterness sensory data.
Attempts to solve the haze problem included boiling the extract with an
addition of wheat gliadin in an attempt to remove many of the polyphenols that
have a tendency to promote haze formation. While there were promising
results, the issue has not been effectively solved. A number of attempts were
executed to remove humulinones from the extract, including some
chromatographic techniques aimed at using a particular solvent polarity to affect the rates at which the polyphenols and humulinones moved through the
chromatographic resins. Isocratic elutions at ethanol concentrations ranging
from 20%-90% showed little effectiveness in separating these compounds,
and gradient elutions, which showed minor efficacies, are difficult to adapt to
large preparative Solid-Phase Extraction columns. The conclusion of the
research saw the production of experimental beer, which was produced to
examine potential varietal differences in the quality of bitterness produced
from hop polyphenols. Two beers were brewed with very high dosings of
spent hops using two hop varieties, Millennium and Australian Topaz. In
future research, these beers will be blended to an appropriate polyphenol level
using an unhopped lager of the same recipe. These treatments will be
presented to a trained sensory panel for descriptive profiling.
Overall, it was found that samples high in polyphenols had intense and
long-lasting bitterness, and that many of the trained panelists found these
samples to have metallic, harsh, and medicinal characters. Astringency was
also affected by the level of hop polyphenols, as samples which were higher in
polyphenols elicited higher astringent sensations for the panelists. There was
little, if any, effect on the time-to-maximum bitterness intensity.
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