may increase or decrease constantly over time, yielding more than
one maximum peak.
Temporal perception of sourness recorded by TDS in some
Gewürztraminer and Riesling wines from 2010 revealed two maxima;
one at the onset of tasting between two and twelve seconds
and a second one starting after 25 s, dominating the aftertaste for
most of the time (Figs. 3a, c, e and 4b and c). Extended skin contact
seems to suppress the second sourness maximum and either bitterness
or astringency dominates the aftertaste. This is also true for the
2009 Gewürztraminer, where sourness only exceeded the chance
level for the whole cluster pressing wine, presumably due to lower
acidity and higher ethanol levels which contribute to the dominance
of sweet and bitter sensations. Due to these modifications of the
second sourness maximum, sourness duration and area were significantly
altered in case of the 2010 Gewürztraminer wines (Table 6).
It may be speculated that the second sourness maximum did not
affect sourness assessment during DA because judges had already
terminated their evaluation procedure at this time. On the other
hand, when astringency became the dominating taste after eight
seconds in case of the skin fermented wine; sourness was still not
perceived as dominating although it received the highest sourness
rating among all wine in this trial during DA (Fig. 1b). Instead of artificially
constructing a holistic profile from discretely evaluated DA
attributes and their intensities, TDS creates a sensory profile over
time, accounting for all relevant attributes at the same time.
Examining the impact of Botrytis infection in combination with
eight hours of skin contact, the second sourness maximum was
also suppressed and instead bitterness and astringency dominated
the taste. However, it remains unclear if the dominance of astringency
in the botrytized wine is due to the formation of new astringent
compounds by the fungus, a better extraction of phenols due
to the fungal enzymes or just a lack of sourness, which could have
masked or at least dominated astringency.
For sweetness, the only significant difference detected by DA
was a lower intensity in the skin fermented 2010 Gewürztraminer
wine. Applying TDS instead, duration and area of sweet dominance
were altered significantly among the six experimental wines
(Table 6). Again the skin fermented wine showed the least sweet
dominance due to the masking of astringency (Fig. 3f). While skin
contact for 35 h and whole cluster pressing were perceived with
less dominating sweetness, skin contact of 0 and 8 h revealed
enhanced sweet dominance. Sweetness perception of the wines
measured by DA and TDS correlated well with glucose and fructose
content in the wines (Table 8). However, this correlation was only
significant for glucose and not for fructose, although fructose content
was higher and is sweeter than glucose at equal concentration.
Thus, similar to bitterness, other wine constituents such as ethanol
and glycerol and lowered sourness might have contributed to
sweetness as well.
Our hypothesis that phenolic compounds are overestimated in
their ability to enhance bitterness can be further supported by
TDS analysis. Although the maximum frequency of bitter dominance
(Dmax) varied from 24% to 48% between the 2010 Gewürztraminer
treatments (Fig. 3a–f), no significance was detected by a
two-way-ANOVA with treatment and replication as fixed effects.
However, examining the coefficients of correlation between total
phenols and all significant sensory parameters provided by the
three applied sensory techniques (Table 8), significant positive correlations
were only observed for bitter Imax and area under the
curve during TI analysis. When the extreme skin-fermented Gewürztraminer
wine was included in the data set, intensity of bitter
and astringency as well as bitter persistency obtained from DA
became significant as well. In conclusion, except for the much
focused TI analysis on bitterness, neither DA nor TDS could detect
any significant correlation of total phenols with any evaluatedsensory attribute in context of skin contact.