Identification of the major drivers of 'phenolic' taste in ... - GWRDC

AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines
pH wine failed to substantially increase its astringency. Phenolics also only significantly increased
hotness when the wine was at the lower end of alcohol in dry white wines (11.4%). At 12.6% alcohol, the
effects of phenolics on hotness were far less pronounced. Overall, low pH levels produced wines that
were more astringent, hot and bitter, and increased alcohol resulted in wines that were more hot and bitter.
Therefore, these two fundamental aspects of pH and alcohol in the wine matrix were shown to have an
overarching effect on those tastes normally associated with phenolics – often greater than the phenolics
themselves.
In moderately alcoholic wines made using a range of commercial practices, perceived astringency and
viscosity were more strongly influenced by pH than by phenolic level. As the degree of skin
contact/maceration increased, so did total phenolics and pH. The higher pH (and phenolic) wines were
perceived to be less astringent, more viscous and more bitter.
To date, wineries have generally measured phenolics as a total ‘pool’ using simple spectrophotometric
methods i.e. absorbance at 280 and 320 nm. Any conclusions drawn from these measures must
necessarily assume that all phenolic species that absorb at these wavelength have a similar taste impact.
This is not likely to be the case. While adding whole phenolics to wine generally increases phenolic
tastes, the presence of some important phenolic species that absorb at these wavelengths appear to have a
suppressive effect also. Therefore, in light of this finding, better rapid analytical methods for measuring
key phenolic subcomponents or classes associated with sensory impacts are required.
Finally, the knowledge that different phenolics or phenolic classes either add or suppress different tastes
arising from phenolics themselves or from the influence of pH or alcohol, could warrant investment in the
development of fining agents that are tailored to modify the tastes and textures of white wine through
removal of key phenolics, or alternatively, may lead to a more effective use of existing fining agents.
Future Research Recommendations and Opportunities
Further opportunities for research into the molecular basis for phenolic taste exist. Of particular relevance
is bitterness, which was one of the few sensory attributes clearly attributable to phenolics but the
molecular drivers remain unknown. Suppressive effects on alcohol hotness and increases in oiliness from
GRP-like compounds may also present opportunities.
While investigating ways of fractionating caftaric acid and GRP from wines using counter-current
chromatography we identified potential new ways of fractionating phenolic compounds identified in our
other studies as potential drivers of the negatively perceived characters of bitterness and metallic taste.
The new HPLC method developed as part of this project can be used to assess the composition and purity
of any resultant fractions submitted to sensory assessment.
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