Richard Gawel

The mouth-feel properties of polysaccharides and anthocyanins in a wine like medium

Abstract Two fractions containing the major polysaccharides present in wine were isolated, one comprising a mixture of neutral polysaccharides, mannoproteins and arabinogalactan-proteins, and the other containing the acidic polysaccharide, rhamnogalacturonan II. A grape anthocyanin fraction was also prepared. A trained sensory panel, using formal sensory descriptive analysis methods to rate the intensity of mouthfeel attributes while the samples were held in the mouth and after expectoration, individually assessed the fractions, dissolved in a model wine at levels commonly encountered in red wines. Both polysaccharide fractions significantly increased the ‘fullness’ sensation above that of the base wine. The rhamnogalacturonan II fraction significantly decreased the attribute ratings associated with the astringency of the model wine whereas the neutral wine polysaccharide fraction had less affect on reducing the ratings for these attributes. The anthocyanin fraction tended to increase ‘fullness’ although the effect was not great enough to be statistically significant. Unlike the polysaccharides, this fraction also increased perceived astringency but this effect could be due to the presence of some derived tannins in the sample.

Use of an experimental design approach for evaluation of key wine components on mouth-feel perception

Abstract To simultaneously explore the primary and interactive effects of proanthocyanidin (‘tannin’), ethanol, anthocyanin and wine polysaccharide concentrations on the mouth-feel perception of wine like media, a sensory study based on an incomplete factorial design was conducted. Two grape polyphenol fractions, i.e. grape seed tannins and anthocyanins, and two fractions of wine polysaccharides, (mannoproteins+arabinogalactan-proteins and rhamnogalacturonan II) were prepared and analysed. A panel of 15 trained judges generated a series of mouth-feel descriptors and rated their intensities while samples containing various levels and combinations of the components were held in mouth and after expectoration. The sensory perception was primarily determined by tannin concentration. However, the attribute ratings were also strongly influenced by all other factors both directly and through interactions. The intensities of all astringency descriptors increased with tannin concentration and were reduced when rhamnogalacturonan II was added. Bitterness increased with ethanol level and decreased in the presence of proteoglycans. Secondary effects observed included both masking and enhancement of the primary effects but also specific interaction effects. The latter are probably related to differences in the structural organization and properties of molecular assemblies involving polyphenols, polysaccharides, and ethanol.

Compositional and Sensory Differences in Syrah Wines Following Juice Run-off Prior to Fermentation

The effect of running off 10% and 20% of juice from two Syrah musts prior to fermentation on the resultant wine sensory properties and composition was investigated. The concentration of total anthocyanins, phenolics and glycosyl-glucose increased and that of glycerol decreased with juice run-off, though the strength of the effects was dependent on the source of the fruit from which the wines were made. Declines in concentrations of anthocyanins, phenolics and glycosyl-glucose from pressing to 6 months of age occurred. The rate of decline was dependent on the fruit source but was independent of the degree of run-off. Formal sensory evaluation showed that run-off enhanced perceived colour intensity, and generally resulted in increased aroma, flavour and astringency.

White wine taste and mouthfeel as affected by juice extraction and processing.

The juice used to make white wine can be extracted using various physical processes that affect the amount and timing of contact of juice with skins. The influence of juice extraction processes on the mouthfeel and taste of white wine and their relationship to wine composition were determined. The amount and type of interaction of juice with skins affected both wine total phenolic concentration and phenolic composition. Wine pH strongly influenced perceived viscosity, astringency/drying, and acidity. Despite a 5-fold variation in total phenolics among wines, differences in bitter taste were small. Perceived viscosity was associated with higher phenolics but was not associated with either glycerol or polysaccharide concentration. Bitterness may be reduced by using juice extraction and handling processes that minimize phenolic concentration, but lowering phenolic concentration may also result in wines of lower perceived viscosity.

Effect of pH and Alcohol on Perception of Phenolic Character in White Wine

The in-mouth perception of textures of white wine arising from the interactions among white wine phenolics, pH, and alcohol level was evaluated. Phenolics were extracted from white wines and added back to white wines that were adjusted to different pH and ethanol concentrations within wine realistic ranges. Adding phenolics to a white wine at pH 3.3 significantly increased its astringency, but the same addition did not contribute to the higher astringency elicited by the same wine when adjusted to pH 3.0. Higher phenolics generally increased bitterness and viscosity, but the effect depended on the source of the phenolics. Wines with added phenolics were generally perceived to be hotter, and significantly so when the wine was low in alcohol. The combined effect of phenolic content and alcohol concentration on astringency and bitterness was additive, suggesting that alcohol directly contributes to these attributes in white wines. Overall, the tastes and textures produced by white wine phenolics were more pronounced in wines with lower alcohol levels.

The Effect of Glycerol on the Perceived Viscosity of Dry White Table Wine

The effect of glycerol on the perceived viscosity of dry white wines was investigated using direct paired comparison sensory methods. Before tasters assessed wines for viscosity, the natural sweetness of glycerol needed to first be masked. This was achieved using two novel methods—prior oral exposure to the anti-sweetness agent Gymnema sylvestre, and by sweetness equalisation using a non-viscous high potency artificial sweetener. After masking its sweetness, the addition of 6 g/L of glycerol did not increase the perceived oral viscosity of dry white wine suggesting that glycerol does not play a role in the perception of dry white wine viscosity. Therefore, palate viscosity in dry white wine cannot be enhanced by employing traditional winemaking approaches that elevate glycerol levels.

The mouthfeel of white wine

ABSTRACT White wine mouthfeel which encompasses the tactile, chemosensory and taste attributes of perceived viscosity, astringency, hotness and bitterness is increasingly being recognized as an important component of overall white wine quality. This review summarizes the physiological basis for the perception of white wine mouthfeel and the direct and interactive effects of white wine composition, specifically those of low molecular weight phenolic compounds, polysaccharides, pH, ethanol, glycerol, dissolved carbon dioxide, and peptides. Ethyl alcohol concentration and pH play a direct role in determining most aspects of mouthfeel perception, and provide an overall framework on which the other minor wine components can interact to influence white wine mouthfeel. Phenolic compounds broadly impact on the mouthfeel by contributing to its viscosity, astringency, hotness and bitterness. Their breadth of influence likely results from their structural diversity which would allow them to activate multiple sensory mechanisms involved in mouthfeel perception. Conversely, polysaccharides have a small modulating effect on astringency and hotness perception, and glycerol does not affect perceived viscosity within the narrow concentration range found in white wine. Many of the major sensory attributes that contribute to the overall impression of mouthfeel are elicited by more than one class compound suggesting that different physiological mechanisms may be involved in the construct of mouthfeel percepts.