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

AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines
measures of heat are indeed generally suppressed by the presence of phenolics, including caftaric acid.
This shows that, in the absence of variations to matrix composition, phenolics may allow winemakers to
‘dial down’ white wine hotness in some circumstances.
Bitterness was, however, generally shown to be positively associated with phenolics. However, the two
major phenolics in Australian white wines (GRP and caftaric acid) do not contribute to bitterness. This
means some other phenolic or phenolic class in white wine does, but their identity remains unknown.
However, various correlative studies consistently implicated flavanol and glycosylated flavonols as
candidates for these bitter tasting compounds.
Observations from winemaking treatments in 2010 show that, as anticipated, increased skin contact
increases phenolics in the wines. However, somewhat unexpectedly astringency decreased and viscosity
increased and this is mostly due to the pH increase (caused by potassium extraction from skins).
Therefore, the desired phenolic outcome of any given winemaking treatment needs to be carefully
considered from the perspective of the concomitant effect of pH on astringency and viscosity.
Observations from winemaking treatments in 2011 (which were adjusted to similar pH’s) show that skin
contact before and during fermentation did not generally differ much in ‘phenolic taste’ compared to
wines made from whole bunch pressed, free run or hyper-oxidised wines despite large differences in
phenolics.
Overall, the notion that all phenolic compounds necessarily contribute to phenolic tastes should be re-
examined in the light of our findings that some either do not affect tastes normally associated with the
presence of phenolics (i.e. bitterness), or indeed caused decreases in others (i.e. astringency).
Furthermore, pH, acidity, and alcohol levels impact strongly on how phenolics manifest themselves in
taste and texture. At low alcohol levels typical of lighter bodied white wines, phenolics contributed to
these tastes and textures, but at higher alcohol levels their impact was less apparent. Therefore,
interpretation of the possible sensory impact of phenolics in lighter bodied white wines requires
consideration of the underlying matrix, particularly pH and alcohol levels.
Implications for broader industry practices
The Australian wine industry has been receptive of new varieties and the uptake of novel processes in the
pursuit of new wine styles. The recent surge in the planting and production of Pinot G to the point where
it is now a commercially important variety in the Australian market is testimony to this. Pinot G. and
other emerging varieties present a new challenge for Australian winemakers, as arguably the phenolics
derived from the grape play a major role in defining their overall structure and style.
Relatively high levels of phenolics (equivalent to the total phenolics encountered in wines made from
hard pressings) when added to a light bodied wine were shown to increase its astringency, bitterness and
viscosity. However, the effect of the phenolics was dependent on the matrix. Adding phenolics to a low
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