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The influence of different oak sources on the flavour profile of red wine
The use of alternative oak products during the vinification of red wines has become standard practice in respect of certain wines in various countries and for a variety of reasons. The origin, appearance and treatment of these products obviously impact on the effect they have on wine. Although the use of alternative products has been common in the younger wine countries for quite some time, it was only legalised in the EU countries in 2006. In view of the fact that the oak barrel still remains the reference for oak maturation, it is important to compare it to the influence of the various alternative products.
The maturation of wine in oak barrels contributes to the sensorial characteristics and colour stability of the wine. The most important flavour compounds extracted from oak are the oak lactones, guaiacol and 4-methyl-guaiacol (which impart a smoky flavour to wine) and vanillin, the concentration of which is also influenced by the toasting process. The pleasant flavour of furfuryl compounds is also formed during the toasting process of the oak. The concentration of the various compounds in wine will be influenced by the origin of the oak, oak treatment and contact period with the oak. The threshold values for the sensorial observation of the various compounds differ and so does the individual tasters' ability to recognise them.
A 2004 Mourvèdre red wine was exposed to different oak treatments once alcoholic and malolactic fermentation had been completed. New and eighth fill 225 litre American oak barrels, medium toasted, were compared with medium toasted American oak chips in three different dimensions (powder, shavings and cubuses). The application dosages of the latter were calculated to concur with the surface-volume ratio of the barrels and amounted to 2.6 grams per litre for the shavings and cubuses and 1.3 grams per litre for the powder. The following combinations were compared in the project:
The analytical results together with statistical analysis thereof showed that significant differences in flavour occurred in wines that received different oak treatments of varying duration. On the whole the oak chips quickly released flavour compounds, whereafter the release stabilised and even decreased when the contact period exceeded 3 months. The wine in the new barrels extracted flavour compounds over longer periods and this is where the highest concentrations of most flavour compounds occurred. The wines in the used barrels with different chip treatments had more extraction than when barrels only were used, although the extraction period did not last as long as with the new barrels.
The use of wood chips by themselves or combined with used barrels may therefore be considered for wines with limited maturation, although new barrels still produce wines with the best overall quality (Bautista-Ortin et al., 2008).
Reference
Bautista-Ortin, A.B., Lencina, A.G., Cano-Lopez, M., Pardo-Mingues, F., Lopez-Roca, J.M. & Gomez-Plaza, E. 2008. The use of oak chips during the ageing of a red wine in stainless tanks or used barrels: Effect of contact time and size of the oak chips on aroma compounds. Australian Journal of Grape and Wine Research 14: 63 - 70.
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