Hayden Jones-Moore, Dr Rebecca Jelley and Professor Bruno Fedrizzi, University of Auckland
Pinot noir is one of the most popular red wines in the world and is the second-largest produced wine in New Zealand, making up 14% of the total vineyard area and 4% of exports. Pinot noir (PN) is a challenging variety and winemakers need a solid understanding of techniques and decisions that can optimise returns through targeting high quality, high price point wines.
Wine polysaccharides are large polymers of simple sugars that are thought to influence many parameters that govern quality including, aroma, mouthfeel, and clarity. Present in both the cell walls of grapes and yeasts, they are released into the wine matrix during maceration, fermentation, and ageing processes. The final concentration and profile of polysaccharides are highly dependent on the variety, vintage, climate, and processing techniques employed.
During maceration, enzymes are often added to enhance the degradation of the grape skin cell wall. This leads to increased grape juice volume, improved clarification, and greater extraction of compounds such as polyphenols, polysaccharides, and aroma precursors. Commercially employed pectinolytic enzymes are employed to break down the complex, ‘tightly-woven’ cell-wall network, releasing polysaccharides. This process modifies the molecular weight (MW) distribution of the polysaccharides and their overall content in the final wine.
The research group at the University of Auckland led by Prof Bruno Fedrizzi and supported by Bragato Research Institute have been investigating and profiling the polysaccharides in New Zealand Pinot noir wines.
Recently the research group have studied the influence of the use of fermentative macerating enzymes during cold soaking on the polysaccharide profile of PN wines. An experiment was carried out where New Zealand PN juice was treated with five commercially available pectinolytic enzymes for four days at 10 °C prior to inoculation with commercial RC212 yeast. In addition to this, a ‘control’ juice sample was also subjected to the same conditions but without enzyme addition, an inoculated control wine. The polysaccharide profile of both the finished wines and the starting PN juice was then quantified using an in-house method.
Research-scale Pinot noir winemaking, cold soak maceration and primary fermentation was carried out in coffee plungers, allowing for pigeage, or punchdown, of the cap multiple times daily. Secondary fermentation was carried out in conical flasks with an airlock and a stopper/bung.
It was postulated that the addition of pectinolytic enzymes during cold soaking may result in higher concentrations of polysaccharides due to increased extractions from the cell-wall network of the grape berry. It was also thought that the increased concentration of enzymes, in addition to the endogenous enzymes released by the yeasts and the naturally occurring grape enzymes, would further assist in extraction of these macromolecules.
However, the results from this experiment identified no significant statistical differences in the polysaccharide profile between the wines produced from juice treated with enzymes and those that were not. As expected, all categories of polysaccharides in the six wines showed statistically increased contents of polysaccharides compared to the juice. The addition of any of the exogenous pectinolytic enzymes species did not significantly out-perform the endogenous enzymes released by the yeast during fermentation, thus none of the enzyme-treated juice samples altered the polysaccharide profile of the wines in comparison to the control. It should be noted that the temperature of the cold soak is below that required for optimal enzyme activity.
These results, in conjunction with commercial yeast strain experiments conducted in 2021 (published in the Research Supplement of New Zealand Winegrowers Magazine Dec 2021/Jan 2022 edition) suggest that the addition of a commercial yeast strain has a more important role in the modulation of the polysaccharide profile of a final wine than the addition of an exogenous macerating enzyme (when added during cold soaking). These results are useful for providing information on the effect these winemaking decisions have on some of the important wine macromolecules that can play a role towards influencing mouthfeel of a finished wine.
About the project:
This three-year project aimed to develop an analytical method to measure high, medium, and low molecular weight polysaccharides in wines and to determine the effect of different yeast strains and different pectolytic enzymes on polysaccharides concentration in Pinot noir wines during winemaking. It was funded by MBIE and NZW levies.