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 oxygen with the aim of oxidising phenolic compounds that might later contribute to phenolic tastes and browning of the finished wine. While almost all phenolic compounds in the juice decrease with hyperoxidation leading to their polymerisation and sedimentation, the polyphenol oxidase induced enzymatic oxidation of hydroxycinnamic acids to form grape reaction products with glutathione and other peptides are the most significant (Cejudo-Bastante et al. 2011). GRP is colourless and relatively unreactive to oxygen. Therefore hyperoxidation generally produces lighter coloured wines that are more resistant to browning than those produced using conventional non-oxidative juice handling methods. While fermentation on skins is rarely practiced in white winemaking on a large scale, some producers make small parcels of wine as blending components in this way. Increased phenolic extraction is achieved by re-incorporating a small proportion of the skins following draining back into the must before yeast inoculation. To date, only small scale laboratory ferments have been used to investigate the effect of skin fermentation on phenolic character. Fermenting in the presence of 100% skins and seeds increased the total phenolic concentration three fold in Ribolla Gialla and two fold in Malvasia wines as compared with a free run control (Bavcar et al. 2011). The catechin and epicatechin concentration of a Chardonnay wine fermented on 0.64 kg/L of skins and seeds was three times higher than in the free run control wine. The skin and seed fermented wines were significantly more astringent and slightly more viscous than the control wine (Oberholster et al. 2009). Fining with proteinaceous agents can be performed on white wines or juices. All have the objective of reducing phenolic content in white wine. They can be chosen in order to remove undesirable coarseness, to protect against future browning, or to remove less soluble phenolics that may cause haziness. Different fining agents have different specificity towards phenolic compounds, which is not surprising given their various modes of chemical binding. As examples, PVPP has been shown to be more effective in removing quercetin compared to its glucoside (LaBorde et al. 2006), and gelatine based agents are more effective at removing non-flavonoids, and less effective in removing monomeric flavanols than casein based fining agents (Braga et al. 2007). Little research has been conducted on the effect of fermenting in the presence of higher levels of suspended grape solids on phenolic content and taste. Singleton et al. (1975) showed that although wines made from juices with higher suspended grape solids were consistently rated as being more bitter and astringent than those made from clarified juice, their total phenolic content did not vary. This result suggests that either fermentation of juices high in solids produces non-phenolic compounds that elicit bitterness and astringency, or fermentation on solids favoured the production of phenolic compounds that better express these sensory characteristics. Alternatively, the extra yeast nutrients provided by the solids can enhance fermentation performance and result in lower residual sugars and higher alcohol content in the finished wine. Both these have the potential to affect taste perception. Page | 18
AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines 1.5 Conclusion White wine contains a diverse set of phenolic substances, all of which could conceivably contribute to ‘phenolic tastes’ in white wine. The possibility that other non-phenolic wine components either directly contribute to or accentuate ‘coarseness’, or accentuate it through wine matrix effects cannot be discounted and also requires further investigation. It also remains to be determined whether individual compounds, or broad classes of phenolic compounds are the key drivers of white wine taste. Without this essential information, it is difficult to define desirable phenolic profiles and to translate detailed phenolic composition into meaningful processing options for the winemaker. Relationships between chemical composition, sensory attributes, and consumer preference need further investigation. With this information, further research could be targeted to key positive or negative sensory characters, enabling the winemaker to better control style and understand consumer preference. Page | 19
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Identification of the major drivers of 'phenolic' taste in ... - GWRDC

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