White wine phenolics
Background
Consumers of Australian white wines seek a range of quality aroma and flavour profiles and enjoy white wine that is elegant and delivers value for money. White wines that are high in phenolics are typically perceived as 'coarse', might lack fresh varietal flavours, can be astringent, have a bitter, hard finish and are prone to oxidation and rapid ageing. This project aims to help white wine makers develop improved methods for managing phenolics in white wines.
Recent innovations and changes to wine processing may have actually impacted on the winemaker’s ability to control phenolic content. Machine harvesting, now widely used, produces greater berry breakage than hand-picking, and therefore, increases extent of contact between juice and stems, seeds and skins. Additionally, wine sector consolidation and growing centralisation of wine processing facilities have created longer transport distances during which such contact may occur. Even at the winery, widely used membrane press technologies can generate a relatively intense contact environment, also possibly increasing phenolics in free-run and press fractions. And once phenolics become present in the wine, control and removal can subsequently prove problematic and costly.
One could argue that problems of high phenolics might be solved by minimising juice contact with skins and other grape or non-grape components. However, this is where the paradox begins: for production of some white wines, some skin contact and phenolics extraction can help achieve a desired stylistic outcome in terms of body and mouth-feel. Winemakers already implicitly understand this and, at the winery, handle and process grapes in ways they believe will achieve that ‘optimum balance’ for flavour and mouth-feel whilst avoiding excessive or undesired coarseness.
Progress
In an endeavour to assist winemakers to manage ‘coarseness’, the AWRI has embarked on a GWRDC-funded project with the University of Adelaide and Pernod Ricard Pacific on white wine phenolics. Our aim is to establish which phenolic compounds are the most important contributors to ‘coarseness’, how they might work together, and what winemaking practices should be implemented to manage these phenolics.
One of the first goals in the project is to quantify the rates at which different phenolic compounds are currently extracted during and after machine harvesting, as well as during processing at the winery. Small-scale winemaking experiments are also planned to assist with the investigations into the effect of harvesting and winemaking processes on phenolics content and final wine quality.
The information gathered during the project will only be fully exploited by Australian wine producers if a tool was available that could rapidly and cost effectively analyse the phenolics composition in juice or wine. Rapid UV, Visible and NIR spectroscopic techniques being developed at the AWRI will be employed to not only evaluate the phenolics in the juice and wine samples collected during the project but could also be subsequently adopted by producers as a rapid instrumental method for this purpose.
At the conclusion of this research it is hoped, ambitious as it may be, that winemakers will be able to more easily and rapidly measure the phenolics profile contained within a batch of juice and, using this knowledge, be able to determine the optimum equipment or steps required in the grape harvesting and wine production processes to better achieve the desired style of wine and therefore optimise the value of the wine product.
Highlights
This project aims to:
- Quantify rates of extraction of phenolics
- Identify compounds responsible for ‘coarseness’
- Develop rapid analytical methods to analyse the phenolics composition in juice or wine
Project leader: Dr Liz Waters
Project team members:
- Patrick Dimanin
- Belinda Bramley
- Dr Paul Smith
- Mango Parker
- Dr Bob Dambergs
- Dr Daniel Cozzolino
- Richard Gawel
- Dr Leigh Francis
- Patricia Osidacz
- Simon Nordestgaard (PhD student)
Collaborators:
- Prof. Brian O’Neill (School of Chemical Engineering, The University of Adelaide)
- Jai O’Toole
- Leon Deans
- Inca Pearce
- Kate Lattey (Pernod Richard Pacific)
Publications:
969 Parker, M.; Mercurio, M.; Jeffery, D.; Herderich, M.; Holt, H.; Smith, P. An overview of the phenolic chemistry of white juice and wine production. Aust. N.Z. Grapegrower Winemaker 509a: 74–80; 2007 (click here to order).
1059 Gawel, R., Dimanin, P.A-G., Francis, I.L., Waters, E.J., Herderich, M.J., Pretorius, I.S. Coarseness in white table wine. Aust. N.Z. Wine Ind. J. 23(3), 19–22; 2008 (click here to order).