Wine In Wood And Wood In Wine: The increasing use of alternative wood products

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Wine In Wood And Wood In Wine
The increasing use of alternative wood products

by Charl Theron, guest lecturer in Oenology, Tim Rypstra, professor in Wood Science and Jan Swart, director: Wood and Fibre Institute, Stellenbosch University.
Alternative oak products such as staves, chips, shavings and powders were initially used in vinification mainly because of the cost benefits. In due course it has almost become standard practice at most wineries. This is mainly because the nature of the products enables precise management of specific characteristics such as toasting level with the accompanying flavour profiles; it is possible to use these alternatives from the crushing of the grapes to maturation; and provided the specifications are clearly prescribed, they are subject to less variation than wooden barrels. The use of micro-oxygenation adds a further dimension to the use of alternative oak products.
In a 2006 survey regarding the use of wood by North American wineries, research was conducted at different size cellars on the use of different forms of oak, the origin of the oak and the use of micro-oxygenation. The following interesting conclusions were reached:

The percentage of wine matured in barrels has decreased. This is especially true of white wines, but the trend was also observed in red wines. This is mainly due to space saving of tanks in which alternative products are used, as opposed to barrels, the subsequent reduction in labour required and the creation of new wine styles where micro-oxygenation is used in conjunction with alternative oak products.
The choice of French, American and Eastern European oak is largely determined by the characteristics imparted to wine, but while French oak still remains the most sought after, American oak retains its cost advantage and Eastern European oak elicits increasing interest.
The use of alternative oak products has increased consistently since 2003. The use of alternatives seems to correlate directly with the decrease in the use of barrels. The use of alternative products made a wide range of oak flavour profiles available to winemakers, while enabling the sustainability of specific wine styles. Of the alternative products, oak chips and cubes remain the most popular format, with oak powder the third most important product.
Micro-oxygenation (MOX) is being used increasingly by cellars. In addition to softening wine tannins, improving the colour stability of red wines, integrating wine flavours and reducing reductive flavours, MOX can also be used with alternative oak products as an alternative to barrel maturation. The reasons for using this method vary from cellar to cellar, the main reasons being cost and an alternative technique to create new wine styles (Pregler, 2006).

Alternative oak products range from fine powder to staves, with a variety of forms and sizes between the two extremes. The various products may be used at different stages in the course of the vinification process.
The addition thereof in the form of fine powder or chips, especially during red wine fermentation, has increased because it reduces the green tannin character of red wines, improves the colour stability and promotes the polymerisation of phenols and anthocyanins. The dosage ranges from 1 to 4 kg per ton of grapes and will also determine the extent to which oak character is imparted to the wine. With Chardonnay fermentations, staves are used mostly at a low dosage. Seeing that untoasted oak still contains oak tannins, which are reduced by toasting, it is logical to use untoasted products for colour stability. But as the tannin levels differ from one tree to the next, and are also leached out of the oak during ripening, the variation in tannin levels obliges winemakers to use toasted products instead.
In recent years the traditional barrel maturation of wines has evolved gradually to bigger barrels. This has resulted in a change in wine style, in that the oak character seems more integrated. By using alternative oak products combined with MOX winemakers are able to manipulate wine styles even more. The dosage at which the products are used, differs considerably. In Chardonnay wines this ranges from 1 to 3 g/litre wine or up to 20% of the barrel surface if staves are used. The wines are left on the lees mostly and stirred for a few months. In red wines usage also varies considerably. Medium to heavily toasted chips may be used for example to impart vanilla flavours to the wine without changing its phenolic character. Up to 2.5 m2 staves may be used per 1 000 litres of wine, if a heavily wooded wine is required for blends. However, most winemakers use 20 to 30% of a barrel surface (ca 1.25 to 2.0 m2 staves per 1 000 litres of wine). If more is used, the wood character will be excessive and unbalanced.
Various volatile compounds deriving from oak contribute to the flavour of wine. During the toasting of wood the thermal breakdown of wood polymers occurs, resulting in the desired flavour compounds. The extent of toasting has a significant effect on this. Oak lactones are probably the most important oak based flavourants, but are not always desirable. Their concentration increases with moderate heating, but reduces with intensive heating. The vanilla and coconut flavours occurring in American oak especially, are lactone based. American oak is also more sensitive to the breakdown of heat, which probably explains why more lactones are found in it. In the case of a toasted stave one can therefore expect the exterior of the stave, which had been exposed to more toasting, to contain more lactones than the interior.
With increased toasting the oak tannins will decompose. This is especially important in the case of alternative products that do not have the same wood depth as barrel dowels.
Further heating will also break down the hemicellulose polymers in simple sugars, causing further breakdown to compounds such as furfurals that taste of caramel and impart toasted, sweet characteristics to the wine. The compounds are usually present on the surface of toasted oak. Heavy toasting of oak will also result in the breakdown of these compounds.
More heat will cause the decomposition of wood lignins, which may cause vanillin and other related compounds. Smoky flavours will only be formed once the oak is heated further.
Theoretically alternative oak products can fulfil the same function as barrels, except that the latter enable a gradual uptake of oxygen. In the case of the alternative products, this role can be fulfilled by MOX. A dosage of 1 to 2.5 ml oxygen/litre wine/month is suggested. The variation in dosage is similar to the difference in permeability of new and used barrels. MOX treatment ensures that the prominence of the oak character is softened.
The physical circumstances of oak maturation play an important role in the optimisation of the process. Temperature control is probably the most important variable in this regard. Maturation at room temperature without any control will expose the wine to unnecessary seasonal temperature variation. Where alternative oak products are applied in wine containers, the temperature will be easier to manage because the temperature of the wine itself may be used. Wine treated in this way will have more fruit and maturation potential than in the case of barrel maturation at fluctuating temperatures (Paul and Gore, 2006).
References:
Paul, R. & Gore, R. 2006. How and why winemakers use barrel alternatives to improve wine quality. Wine Industry Journal 21(5): 34 - 37.
Pregler, P. 2006. 2006 Barrel and Oak Report. Wine Business Monthly December 2006: 28 - 35.

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