Ellagitannins
Ellagitannins are a class of hydrolysable tannins derived primarily from oak wood and other hardwoods used in cooperage. In winemaking, ellagitannins are extracted into wine during oak ageing and contribute to structure, mouthfeel, oxidative behaviour and long-term stability.[1]
Origin and chemistry
Ellagitannins are polyphenolic compounds formed from hexahydroxydiphenic acid units esterified to a glucose core. They are distinct from the condensed tannins (proanthocyanidins) found naturally in grape skins, seeds and stems.[2]
In winemaking, ellagitannins originate almost exclusively from wood, especially oak species such as Quercus robur, Quercus petraea and Quercus alba. Their concentration and composition vary according to oak species, forest origin, seasoning, toasting level and barrel age.[3]
Extraction during oak ageing
Ellagitannins are extracted from wood into wine during barrel ageing or contact with oak alternatives such as staves or chips. Extraction is most pronounced in the early stages of wood contact and declines as barrels age and ellagitannin reserves are depleted.[4]
Their extraction is influenced by wine composition (notably alcohol level and pH), temperature, surface area of wood contact and duration of ageing.
Role in wine structure and ageing
Ellagitannins contribute to wine structure by increasing perceived astringency and reinforcing tannin backbone, particularly in red wines. They can interact with grape-derived tannins and anthocyanins, influencing colour stability and mouthfeel evolution over time.[5]
A key functional role of ellagitannins is their participation in controlled oxidation processes. They act as oxygen scavengers and redox mediators, helping regulate oxygen transfer during barrel ageing and reducing the risk of premature oxidation.[6]
Sensory impact
Sensory effects of ellagitannins include firmness, dryness and structural grip. In balanced concentrations, they contribute positively to complexity and ageing potential; in excess, they may produce harsh or bitter sensations, particularly in wines with limited fruit concentration.[7]
Their sensory perception evolves during bottle ageing as ellagitannins undergo hydrolysis and polymerisation reactions.
Winemaking considerations
Winemakers manage ellagitannin impact through choices of oak origin, barrel age, toast level and duration of ageing. New barrels contribute the highest ellagitannin load, while neutral barrels primarily facilitate oxygen exchange with minimal tannin input.[8]
Regulatory frameworks governing the use of wood and oak-derived products in winemaking are established by the OIV and national authorities.[9]
See also
References
- ↑ Jancis Robinson, Oxford Companion to Wine, Oxford University Press, 17 Sept. 2015. ISBN 9780198705383.
- ↑ Andrew L. Waterhouse, Understanding Wine Chemistry, Wiley, 19 Aug. 2016. ISBN 9781118627808.
- ↑ Cheynier et al., Wine Chemistry and Biochemistry, Elsevier, 2012, ISBN 9780123884381.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Volume 2, Wiley, 2006, ISBN 9780470010396.
- ↑ PhD Jackson, Ronald S., Wine Science: Principles and Applications, Academic Press Inc, 14 April 2020. ISBN 9780128161180.
- ↑ Vivas & Glories, “Ellagitannins in oak and wine”, Journal of Agricultural and Food Chemistry, ISSN 0021-8561.
- ↑ Peynaud, Knowing and Making Wine, Wiley, 1984, ISBN 9780471881491.
- ↑ 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.
- ↑ OIV, “Use of wood in oenology”.