was enhanced significantly by 8 and 24 h of skin contact in the
2009 Gewürztraminer wines although residual sugar remained
equal among the wines (Tables 4 and 7).
TDS further revealed that the wine made from B. cinerea
infected Gewürztraminer grapes in 2010, was significantly less
sour, although adjusted to a similar total acidity (9.0 and 8.7 g/L
respectively; Table 7). Taking a closer look at the acid composition
in Table 7, the wines made from sound grapes were lower in malic
acid but higher in tartaric acid than the wine made from infected
grapes. Thus, it seems that the difference of 0.9 g/L tartaric acid
was able to trigger a significant lower duration and area of the sour
dominance curve for the wine made from infected grapes.
Examining the molecular base for the significant modification of
bitterness and astringency triggered by skin contact, phenol content
in Table 7 was not able to explain the observed differences
in a comprehensible manner. Comparing whole cluster pressing
and 35 h of skin contact in the 2010 Gewürztraminer trial, the
increase of 70 mg/L total phenols (Table 7) increased bitter Imax
and area under the curve significantly, while an even larger difference
of 92 mg/L total phenols between 0 and 35 h of skin contact,
failed to be significant for the bitter TI parameters. It is also noteworthy
that the huge increase of 500–600 mg/L total phenols due
to skin fermentation only yielded a modest increase of 20–40% in
the bitter TI parameters Imax and area under the curve.
Singleton et al. (1975) was even unable to detect any significant
modification in bitterness by comparing wines made without any
skin contact and wines fermented on the skins for five days. This
could be rationalized by a much smaller increase in total phenols
in Singleton’s study, presumably due to larger berry diameters of
Chenin Blanc and French Colombard grapes used by the authors
versus the small berry diameters of Gewürztraminer in our study.
Oberholster et al. (2009) could also not find any significant difference
for bitter intensity among experimental wines, which were
supplemented at the juice stage prior to fermentation with phenolic
fractions derived from grape skins or seeds. Although catechin
and epi-catechin were modified significantly in the finished wines,
this was not sufficient to trigger a significant sensory signal.
Comparing bitter areas under the TI curve of Riesling versus
Gewürztraminer, the Riesling was perceived as more bitter, except
for the extreme skin fermented Gewürztraminer wine (Table 5).
Not only higher total phenols may have triggered this difference
(128–220 mg/L for Gewürztraminer and 185–281 mg/L for Riesling;
Table 7) but also the fact that Riesling wines were, on average,
7 g/L or 0.8% vol. higher in ethanol than 2010 Gewürztraminer
wines.
Examining the correlation coefficients for glucose, fructose and
ethanol in the experimental wines in Table 8, sugars proved to
Table 6
Post hoc test (LSD, a = 0.05) for those parameters extracted from TDS curves which were significantly different among the 2009 and 2010 Gewürztraminer wines.a
Sensory modalities Sweet Sour Astringent
Parameters from TDS curves Dmax Duration Area Dmax Duration Area Dmax Duration Area
Gewürztraminer 2009
Whole cluster pressing – – – – a a – – –
0 h skin contact – – – – ab b – – –
8 h skin contact – – – – b b – – –
24 h skin contact – – – – b – – –
Gewürztraminer 2010
Whole cluster pressing – bc bcd – b a bc c bc
0 h skin contact – abc abc – c b bc c c
8 h skin contact – a a – a a c c c
8 h skin contact + Botryis – ab ab – c b b b b
35 h skin contact – cd cd – a a bc c bc
Fermentation on skins – d d – d b a a a
The difference between levels with the same letter is not significant. Not significant results are denoted with ‘–’.
a Tests were calculated separately for the wines of each grape variety and vintage.
was enhanced significantly by 8 and 24 h of skin contact in the2009 Gewürztraminer wines although residual sugar remainedequal among the wines (Tables 4 and 7).TDS further revealed that the wine made from B. cinereainfected Gewürztraminer grapes in 2010, was significantly lesssour, although adjusted to a similar total acidity (9.0 and 8.7 g/Lrespectively; Table 7). Taking a closer look at the acid compositionin Table 7, the wines made from sound grapes were lower in malicacid but higher in tartaric acid than the wine made from infectedgrapes. Thus, it seems that the difference of 0.9 g/L tartaric acidwas able to trigger a significant lower duration and area of the sourdominance curve for the wine made from infected grapes.Examining the molecular base for the significant modification ofbitterness and astringency triggered by skin contact, phenol contentin Table 7 was not able to explain the observed differencesin a comprehensible manner. Comparing whole cluster pressingand 35 h of skin contact in the 2010 Gewürztraminer trial, theincrease of 70 mg/L total phenols (Table 7) increased bitter Imaxand area under the curve significantly, while an even larger differenceof 92 mg/L total phenols between 0 and 35 h of skin contact,failed to be significant for the bitter TI parameters. It is also noteworthythat the huge increase of 500–600 mg/L total phenols dueto skin fermentation only yielded a modest increase of 20–40% inthe bitter TI parameters Imax and area under the curve.Singleton et al. (1975) was even unable to detect any significantmodification in bitterness by comparing wines made without anyskin contact and wines fermented on the skins for five days. Thiscould be rationalized by a much smaller increase in total phenolsin Singleton’s study, presumably due to larger berry diameters ofChenin Blanc and French Colombard grapes used by the authorsversus the small berry diameters of Gewürztraminer in our study.Oberholster et al. (2009) could also not find any significant differencefor bitter intensity among experimental wines, which weresupplemented at the juice stage prior to fermentation with phenolicfractions derived from grape skins or seeds. Although catechinand epi-catechin were modified significantly in the finished wines,this was not sufficient to trigger a significant sensory signal.Comparing bitter areas under the TI curve of Riesling versusGewürztraminer, the Riesling was perceived as more bitter, exceptfor the extreme skin fermented Gewürztraminer wine (Table 5).Not only higher total phenols may have triggered this difference(128–220 mg/L for Gewürztraminer and 185–281 mg/L for Riesling;Table 7) but also the fact that Riesling wines were, on average,7 g/L or 0.8% vol. higher in ethanol than 2010 Gewürztraminerwines.Examining the correlation coefficients for glucose, fructose andethanol in the experimental wines in Table 8, sugars proved toTable 6Post hoc test (LSD, a = 0.05) for those parameters extracted from TDS curves which were significantly different among the 2009 and 2010 Gewürztraminer wines.aSensory modalities Sweet Sour AstringentParameters from TDS curves Dmax Duration Area Dmax Duration Area Dmax Duration AreaGewürztraminer 2009Whole cluster pressing – – – – a a – – –0 h skin contact – – – – ab b – – –8 h skin contact – – – – b b – – –24 h skin contact – – – – b – – –Gewürztraminer 2010Whole cluster pressing – bc bcd – b a bc c bc0 h skin contact – abc abc – c b bc c c8 h skin contact – a a – a a c c c8 h skin contact + Botryis – ab ab – c b b b b35 h skin contact – cd cd – a a bc c bcFermentation on skins – d d – d b a a aThe difference between levels with the same letter is not significant. Not significant results are denoted with ‘–’.a Tests were calculated separately for the wines of each grape variety and vintage.
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