Volatile phenols
Volatile phenols are a group of aromatic phenolic compounds in wine that readily evaporate and are detectable by smell. They are best known for their association with certain wine faults, but in low concentrations they may contribute complexity to aroma, depending on wine style and context.[1]
Definition and chemical nature
Volatile phenols are phenolic compounds characterised by relatively low molecular weight and sufficient volatility to influence wine aroma. Chemically, they originate from hydroxycinnamic acids naturally present in grapes, which are transformed through microbial metabolism into aromatic phenols such as 4-ethylphenol and 4-ethylguaiacol.[2][3]
Although phenols are often discussed in relation to colour and structure, volatile phenols are distinct in that their primary impact is olfactory rather than tactile or gustatory.[4]
Origin and formation
The formation of volatile phenols in wine is primarily microbiological. Certain yeasts and bacteria possess enzymes that decarboxylate and reduce grape-derived hydroxycinnamic acids into volatile phenols. The yeast genus Brettanomyces (also known as Dekkera) is the most significant contributor, particularly in red wines aged in barrel.[5][6]
Wood ageing, oxygen exposure, and insufficient microbial control can favour the development of these compounds, although their presence is not exclusively linked to barrel ageing.[7]
Sensory impact
Volatile phenols are associated with a range of distinctive aromas. Common descriptors include barnyard, stable, leather, medicinal, smoky, clove-like, and sometimes plastic or adhesive notes. The specific sensory expression depends on the relative proportions of individual compounds and the wine matrix.[8][9]
At low concentrations, some tasters perceive certain volatile phenols as contributing savoury or spicy complexity. At higher levels, they are widely regarded as faults that obscure varietal and regional character.[10]
Control and prevention
Management of volatile phenols focuses on limiting the growth of spoilage microorganisms and reducing their metabolic activity. Preventive measures include strict hygiene, appropriate sulfur dioxide management, controlled oxygen exposure, and monitoring during ageing and storage.[11][12]
Analytical monitoring allows early detection of volatile phenols, supporting quality control decisions in both cellar and distribution stages.[13][14][15]
Economic and stylistic considerations
The presence of volatile phenols has economic implications, as wines affected beyond acceptable thresholds may be declassified or rejected by markets. Conversely, tolerance levels vary across regions and consumer segments, influencing stylistic debates around authenticity and fault perception.[16][17]
References
- ↑ Jancis Robinson, Oxford Companion to Wine, Oxford University Press, 17 Sept. 2015. ISBN 9780198705383.
- ↑ PhD Jackson, Ronald S., Wine Science: Principles and Applications, Academic Press Inc, 14 April 2020. ISBN 9780128161180.
- ↑ Andrew L. Waterhouse, Understanding Wine Chemistry, Wiley, 19 Aug. 2016. ISBN 9781118627808.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Volume 2, Wiley, 2006, ISBN 9780470010396.
- ↑ Kenneth C. Fugelsang, Wine Microbiology, Springer, July 31, 1997. ISBN 9780412066115.
- ↑ Roger B. Boulton, Vernon L. Singleton, Linda F. Bisson, Ralph E. Kunkee, & 1 more, Principles and Practices of Winemaking, Springer, 31 Oct. 1998. ISBN 9780834212701.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Volume 2, Wiley, 2006, ISBN 9780470010396.
- ↑ Chatonnet et al., “Brettanomyces and volatile phenols”, American Journal of Enology and Viticulture, ISSN 0002-9254.
- ↑ Stevenson, The Sotheby’s Wine Encyclopedia, DK, 2011, ISBN 9780756686840.
- ↑ Karen MacNeil, The Wine Bible, Workman Adult, October 11, 2022. ISBN 9781523510092.
- ↑ PhD Jackson, Ronald S., Wine Science: Principles and Applications, Academic Press Inc, 14 April 2020. ISBN 9780128161180.
- ↑ OIV, “Phenolic compounds and wine aroma”, https://www.oiv.int
- ↑ UC Davis, “Volatile phenols and wine faults”, https://wineserver.ucdavis.edu
- ↑ AWRI, “Managing volatile phenols”, https://www.awri.com.au
- ↑ FAO, “Microbial impacts on wine quality”, https://www.fao.org
- ↑ Anderson, The Economics of Wine, Edward Elgar, 2010, ISBN 9781847201006.
- ↑ Anderson & Pinilla, Wine Globalization, Cambridge University Press, 2018, ISBN 9781108445687.