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44 WINES&VINES February 2016 BARRELS PRACTICAL WINERY & VINEYARD W hile varia- tion in oak b a r r e l s ' contribu- tion to wine is generally accepted by winemakers, this variation can have un- intended impacts on wine composition and the eco- nomics of production. To reduce this variability, it is important to understand oak chemical composition. Wood-extractable compounds can be directly transferred from oak to wine. They are extracted during winemaking and élevage in barrels, and the extraction rate can vary depending on wood and wine. Even if wood-extractable compounds represent a minor component of total oak chemistry, they play an important role in wine style. In this group there are ellagi- tannins (representing the majority of oak-extractable compounds) and a pool of aromatic compounds present in untoasted wood (native aromatic compounds) that are responsible for oaky aromas. For example, whisky lactones are responsible for coconut and fresh wood notes but also con- tribute to wine freshness and fruitiness. Non-extractable com- pounds, while not extractable as such, are precursors of volatile compounds produced during the toasting process. The degradation of hemicel- luloses during barrel toasting gen- erates compounds responsible for toasted/roasted aromas, whereas lignins generate compounds re- sponsible for vanilla/pastry nu- ances and spicy and smoky notes. The amount produced during toasting varies according to time, temperature and wood humidity. Toasting also degrades ellagitan- nins and can increase or decrease oaky notes (whisky lactones) de- pending on temperature. Thus, the contribution of these different compounds to wines at the end of élevage can vary de- Innovative Tools for Stave Selection and Toasting Uncovering the impact of oak on wine style and composition By M.L. Badet-Murat, J.C. Vicard, A.A. Watrelot and J.A. Kennedy Ellagitannins, while a small percentage of oak chemical compounds, are highly extractable and play an essential role in winemaking. OAK WOOD COMPOSITION TOASTING TOASTING VARIABLE EFFECT OAK QUALITY TOASTING MANAGEMENT DEGRADATION NON- EXTRACTABLE 90%-95% Ellagi- tannins Whisky lactones Vanilla notes Spicy notes Toasted notes 5%-10% EXTRACT- ABLE LIGNIN CELLULOSE HEMICELLU- LOSE