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

More documents

Recommendations

Info

AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines precipitated by a salivary like protein when more alcohol was present (Pascal et al. 2008). To date, all the studies investigating the role of alcohol on astringency perception have used, or contained, polymerised phenolics that did not constitute a significant proportion of the phenolic fraction used in this study which was dominated by the presence of the small molecular weight phenolics particularly hydroxycinnamates. This may explain why no significant effect of alcohol was observed here. While adding 30% more phenolics did not significantly increase bitterness (p=0.217), a consistently higher bitterness under all combinations of alcohol and pH was observed (Figure 5-1 (B)). Perceived bitterness decreased with the addition of alcohol (p=0.079). The enhancing effect of alcohol on the bitterness of the phenolics was at odds with Fontoin et al. (2008) when adding oligomeric flavanols (mean degree of polymerisation of 2.1) to model wine and Fischer and Noble (1994) when adding the monomeric flavanol catechin to de-alcoholised wine. The increase in perceived bitterness of the phenolic compounds at lower pH was clear (p=0.001). Fontoin et al. (2008) found no effect, while Fischer and Noble (1994) reported a small increase over a similar pH range to that studied here. The reason for the differences in effects resulting from alcohol and pH is unclear but may relate to the different phenolics used in the respective studies. Some tasters find alcohol sweet (Skinska et al. 2000). The effect of adding alcohol on bitterness perception was purely subtractive (phenolic x alcohol p=0.972) which lends weight to the possibility that the alcohol sweetness masked the bitterness of the phenolics in this case. We also used a food grade alcohol distilled from grapes, while the other studies used analytical grade ethanol. So this may also have been a factor. The effect of pH on bitterness perception was also strongly additive (pH p=0.001, phenolics x pH p=0.770) with lower pH resulting in greater bitterness. Fontoin et al. (2008) found no effect of pH on the bitterness of oligomeric flavanols, and using catechin Fischer and Noble (1994) found a small increase with decreasing pH over the range used in this study, but an inconsistent trend over a wider pH range. In the earlier studies, pH was increased by titrating with NaOH. Our use of a real wine as a base required the reduction in pH using a strong inorganic acid. The different counterions that necessarily are included by such practices may explain the differences across studies. However, it could be expected that the method used here to modify pH was less intrusive than the earlier approaches as the base used here was a commercial wine that required little adjustment. Not surprisingly, adding alcohol to the base wine made it taste ‘hotter’ (p
AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines 3). The highest alcohol used in this study was 12.6% v/v which is representative of light bodied white wines. The effect of adding 30% more phenolics on the perceived hotness of a 12.6% v/v alcohol wine was relatively small. So while it was demonstrated that phenolics have the capacity to contribute to hotness in white wine, it seems likely that in fuller bodied styles that are typically higher in alcohol than 12.6% v/v, the impact of phenolics on hotness is likely to be small – and it is in these higher alcohol styles where winemakers are more likely to employ methods that increase phenolics (i.e. skin contact, pressing addition). Later, it was shown that the hotness displayed by wines with an average 13.2% v/v alcohol but made using winemaking methods that increased their total phenolic levels by up to 70% did not differ in perceived hotness (Chapter 8). Lowering the pH also resulted in an increase in perceived ‘hotness’ at both alcohol levels (p=0.004). The reason for this is unclear, but the lack of interaction with phenolics (p=0.384) and alcohol (p=0.984) suggests that the increased hotness was a direct effect of pH. Perceived acidity elicited by the Riesling base wine appeared to be accentuated by phenolic addition but only at the lower alcohol level (p=0.057, Figure 5-1(D)). The wine that the phenolics was extracted from was characterised by HPLC as having a relatively high level of hydroxycinnamic acids (data not shown) - which is typical of Riesling wines made using reductive winemaking processes. While hydroxycinnamic acids are weak acids, in combination they may contribute to the acid taste of the wine. However the role of other phenolic compounds cannot be ruled out as more defined phenolic fractions that contained a smaller number of hydroxycinnamic acids did not increase the wine acidity (Chapter 6). Page | 43 Table 5-1: Significance (p values) of effect of composition on sensory. Astringency Hotness Bitterness Acidity Phenolics 0.046 0.000 0.217 0.278 Alcohol 0.524 0.000 0.079 0.009 pH 0.074 0.004 0.001 0.130 Alcohol x Phenolics 0.819 0.012 0.972 0.164 Alcohol x pH 0.302 0.984 0.183 0.057 pH x Phenolics 0.095 0.384 0.770 0.957 Alcohol x pH x phenolics 0.916 0.021 0.144 0.355 Bold highlight indicates statistical significance (p
Page 1 and 2: Identification of the major drivers
Page 3 and 4: AWRI: Identification Of The Major D
Page 41: AWRI: Identification Of The Major D
Page 93 and 94:
AWRI: Identification Of The Major D
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
RT (min) AWRI: Identification Of Th
Page 115 and 116:
RT (min) AWRI: Identification Of Th
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139:
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?