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

AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines
juice handling, but only at the expense of caftaric acid. Caftaric acid was shown to reduce the burning
hotness from alcohol and GRP was shown to increase palate oiliness.
The discovery that these two phenolics decrease the dry mouth-feel produced by alcohol and acidity, and
caftaric acid suppressed alcohol hotness was unforeseen. It has long been assumed that most ‘phenolic
taste’ elements came from phenolics and that the wine matrix (e.g. acid, alcohol) modulated these
perceptions, so the finding that some principal phenolic taste characteristics come from the matrix and are
then modulated by some phenolics was unexpected. This has significant practical implications because
these two compounds can be varied in winemaking through oxygen exposure and so variations in their
concentrations, and that of similar compounds, may allow modulation of the significant sensory effects
from alcohol and pH.
An advanced HPLC method has been developed and now allows separation of > 80 identified (40 of
which can currently be quantified) phenolics in white juices and wines. This is a notable advancement on
the previous methods available, in particular because it requires minimal sample preparation. This was a
challenging aspect to the project that was critical to analysing the winemaking experiments described
next.
We produced a set of white wines that varied greatly in phenolic composition, so as to elicit measurable
differences in both taste and texture. A mix of both conventional and less practiced white wine making
techniques were used over three vintages and most winemaking treatments were repeated over two of the
years (2010 and 2011). The winemaking experiments, together with the outcomes of the previous
experiments in the project, allow insight into the molecular basis of ‘phenolic’ taste which is summarised
below.
‘Astringency’ ratings in white wines were found to be strongly negatively correlated with pH (i.e. lower
pH gives higher astringency). Aggregate measures of phenolics, various complex mixtures of phenolic
compounds, and the two major individual phenolics (caftaric acid and GRP) were, in general, not
particularly associated with astringency. A striking example of this is the minimal difference in
astringency between low phenolic hyper-oxidised wines and the high phenolic macerated and skin contact
wines made in 2011. These are among several findings of significance that contradict the widely held
assumption that phenolics are the main cause of astringency in white wines.
‘Viscosity’ ratings in white wines were found to be strongly positively correlated with pH (i.e. lower pH
gives lower viscosity). This new discovery further emphasises the importance of this matrix effect on the
perception of mouth-feel in white wines.
‘Hotness’ and ‘burning after taste’ are most highly associated with alcohol concentration, not aggregated
phenolic measurements or caftaric acid. Phenolics have anecdotally been implicated in these sensory
characteristics, but mostly phenolics seem not to be positively related to these heat attributes, with the
exception of some small effects from GRP and GRP-like compounds. In a further discovery, these
95