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

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AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines were the result of pH rather than phenolic level. The observed relationship between viscosity and pH has not been reported before. Anecdotally, the mouth-feel of high pH wines has sometimes been described as ‘soapy’, which may relate to viscosity. However, while this explanation is speculative, the very strong relationship between pH and viscosity suggests that the effect of pH on viscosity may be a direct one. In order to assess the role of other factors other than pH on the astringency of these wines, the strong linear effect of pH was subtracted from the total observed effect to obtain a ‘residual’ effect attributable to other factors including phenolics. The same strategy was applied to the viscosity ratings. A significant difference in astringency following the removal of the pH effect was observed (p=0.058), suggesting that other factors including phenolic content contributed to the astringency of these wines. There was no overall effect of winemaking treastments on difference in pH adjusted viscosity as the observed effects were variety dependent. There were no significant differences in hotness resulting from the winemaking treatments (p=0.349), (Table 8-3). There was a significant difference in bitterness between samples (p=0.13), with bitterness increasing in the order of increased maceration and total phenolics (Figure 8-15). While bitter aftertaste did not differ statistically (p=0.239) it increased in a parallel fashion to in-mouth bitterness. 84 Table 8-3: Significance (p values) for experimental effects 2010 wines Astringency adj for pH Viscosity adj for pH Bitter Bitter AT Hotness Variety 0.787 0.589 0.497 0.492 0.542 Treatment 0.058 0.392 0.013 0.239 0.349 Variety*Treatment 0.550 0.055 0.833 0.455 0.841 Ferment(Treatment) 0.918 0.559 0.975 0.668 0.442 Bold indicates statistical difference (p
AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines Figure 8-18 (individual varieties in Figure 8-19) gives the mean sensory attribute ratings of the 2011 wines by treatment and variety, and Table 8-4 the significance of treatment effects. Significant effects were seen for astringency, viscosity (including when adjusted for pH effects) and bitterness. There was also weak evidence for winemaking treatment on metallic and oiliness. However, the effect of winemaking on the wines taste properties was strongly dependent on variety. When averaged across varieties, skin maceration resulted in the highest astringency and bitterness, while maceration produced the lowest intensity of both these attributes. These results were despite these two treatments having the same high A280, suggesting that the wines had equivalent total phenolic content (Figure 8-6). Therefore either the differences in the respective wine matrices are affecting perception, or the differences are due to variations in phenolic profile. The high overall average bitterness of the low phenolic hyperoxidised free run wines is also noteworthy as higher bitterness is normally associated with higher phenolics. The solids ferment wines consistently displayed higher level of metallic character across the three varieties, and were on average one of the most oily, hot and burning of the treatments. With the exception of an early study by Singleton et al. (1975), the textural properties of wine resulting from the relatively common practice of fermenting juice containing grape solids has been not been reported. The early work found that fermenting turbid juices did not cause an increase in total wine phenolics, but it did result in consistently more bitter and astringent wines. We found that solids fermentation impacted on total phenolics, total hydroxycinnamates and flavanoid extract, but the effect was variety dependent. Higher solids resulted in higher flavanoid extract in all three varieties compared with the free run wines. The total phenolics were the same for the Riesling and Viognier wines, but the Chardonnay wines fermented on solids had nearly twice the total phenolics as did the free run wines. The presence of grape particles in a must could provide a source of compartmentalised phenolics that are liberated during alcoholic fermentation. This may explain the unique textures displayed by the solids wines in this trial. 85 Intensity 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 All Wines Astringency Viscosity Hotness Bitter Metallic Oily Burning AT HOX-FR WBP HOX-HP FR SOL HP MAC SKI Figure 8-18: Mean intensity ratings of attributes associated with ‘phenolic taste’in 2011 wines. All wines. Treatments ordered from lowest to highest in average A280. Bars show 10% LSD.
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Identification of the major drivers of 'phenolic' taste in ... - GWRDC

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