Wine taints and off-flavours
Background
Taints and off-flavours in wines may be derived from numerous sources, but regardless of their origin, they negatively impact on the quality of a wine. Off-flavours can be related to the presence of various undesirable compounds during the winemaking process, such as hydrogen sulfide for example, while taints may originate from contamination of the wine through corks, barrels or any number of steps along the wine production and supply chain.
Typically, a combination of sensory evaluation, GC-MS-O (Gas chromatography-mass spectrometry-olfactometry), and GC-MS are used to identify the compound responsible for the taint. The source of contamination can then be identified and corrective measures can be implemented. We also develop methods for the identification and analysis of taint compounds and synthesis of reference compounds and labeled analogues.
Progress
A number of methods have been developed for the analysis of low molecular weight thiols which may be responsible for undesirable characters such as reduced aromas in wines. A sensitive, sulfur-specific detector coupled to a GC is used for this work.
When a plastic-like taint was suspected to be contaminating commercial wines, several winemaking additives were investigated. GC-MS analysis coupled with olfactory detection enabled the identification of 6-chlorocresol (6-CC), which is one of the most potent chlorophenols known. A sensitive method was validated for the analysis of 6-CC in wines and a range of tainted wines were analysed for this compound.
Some wines with a plastic-like taint were found not to have any 6-CC, or only very low levels which could not account for the taint. Using GC-MS techniques,, the contaminant was found to be a dichlorinated phenol which was described as 'antiseptic', 'chlorine' and 'chemical'/'plastic-like'. Again, a sensitive method was validated for analysis of this chlorophenol and a large number of tainted wines were analysed for its presence.
Yet another plastic-like off-flavour was observed but could not explained by the presence of chlorophenols. Indole, which is derived from bacterial metabolism and has an unpleasant 'plastic'/'chemical' aroma, was found to be responsible for these affected wines. A sensitive GC-MS method was developed and validated for the quantitation of indole, and from analysis of a range of wines it was found that indole was generally detected, even in wines not presenting an obvious off-flavour. Problems occurred in wines which had indole levels some 30 times higher than those found in unaffected wines.
Taint problem-solving and method development for off-flavours are important and continuing avenues of research.
Highlights
- Analysis of low-molecular weight thiols is achieved using a sensitive, sulfur-specific detection analytical method
- 6-CC was identified as the cause of a taint issue and a method was developed for analysis of 6-CC in wine samples
- Another chlorophenol was determined as the cause of a taint problem and a method was developed for its analysis in wine samples
- A separate off-flavour issue was related to the presence of indole and a method was developed for the analysis of this compound in wines
- Indole was found to be a normal component of most wines and only posed a taint problem when it was present above approximately 30 µg/L
Project leader: Dr David Jeffery / Dr Yoji Hayasaka
Project team members:
Publications:
1039 Coulter, A.D.; Capone, D.L.; Baldock, G.A.; Cowey, G.D.; Francis, I.L.; Hayasaka, Y.; Holdstock, M.G.; Sefton, M.A.; Simos, C.A.; Travis, B. Taints and off-flavours in wine - case studies of recent industry problems. Blair, R.J.; Williams, P.J.; Pretorius, I.S. (eds). Proceedings of the thirteenth Australian wine industry technical conference, 29 July-2 August 2007, Adelaide, SA. Australian Wine Industry Technical Conference Inc.: Adelaide, SA: 73-80; 2008 (click here to order).