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42 WINES&VINES February 2017 WINEMAKING PRACTICAL WINERY & VINEYARD F or many years, the cooperage industry developed tools to select and classify oak with the goal of ensuring quality, precision and reproducibility in their barrels. Selection on the basis of geo- graphic origin dates back to the early 19 th century. 1,2 Selection according to morphological criteria such as the width of growth rings (grain), closely linked to forestry manage- ment methods and botanical species, was first applied about 50 years ago. 3,4,5,6 In re- cent years, the market for fine-grain oak has grown dramatically. Some forests are so sought after that sourcing has become dif- ficult, which in the long term could lead to the total depletion of large-diameter (60-80 cm) fine-grain wood resources. Recent extensive research in the variability of the chemical composition of oak has high- lighted an alternative selection criterion. In- deed, while selection by forest and/or grain is useful for controlling barrel quality, it does not reflect the tremendous variations in com- position, both on an inter- 7,8,9,10,11,12 and intra- individual level. 11,13,14,15 Barrel quality control and reproducibility are key concerns for winemakers, as barrel aging forms an integral part of each wine's distinctive signature, and the choice of bar- rels can result in significant changes in a wine's sensory profile. For example, one experiment on four lots of 10 barrels re- vealed that a single barrel was capable of inducing a 50% variation in concentrations of major volatile compounds from oak in the final blend. 16 Given this new data, the challenge for winemakers is to obtain barrels of known, homogeneous, reproducible quality. Therefore, it is necessary for the cooperages to control the concentration of extractable compounds in oak. In 2009, Groupe Vicard launched a re- search program aimed at controlling variability factors during barrel making. This research led to the development of a specific range (Vicard Generation 7) based on wood selected according to its ellagitannin content. 12 Ellagitannins represent the majority of extractable compounds and contribute significantly to variations in composition and quality during élevage. 17,18,19,20 Analysis using near-infrared spectrometry identified three main classes of tannin potential correspond- ing to distinct ellagitannin contents in un- toasted wood. This analytical approach to wood selec- tion was accompanied by other innovations aimed at controlling the factors responsible for variability in cooperage: scarification of the staves (blister-free process consisting of micro-slits to allow water locked in the wood to escape naturally during the toasting pro- cess), short, automated steam-bending, and a unique process for toasting not previously used in cooperage. Toasting using radiant heat in a fully automated and computer- controlled, closed system guarantees homo- geneity, reproducibility and precision. 12 This system also makes it possible to ad- just toasting according to the tannin level of the oak. Because thermal degradation of ellagitannins varies according to toasting time and temperature, 9,21 it is necessary to adapt toasting parameters to different tannin potentials. This is a fundamental aspect of this approach, because without complete control of the toasting process, the upstream classification of oak on the basis of its tannin content would be meaningless. Combining this new oak selection and classification criterion with the toasting sys- tem described above produces barrels with known, homogeneous, reproducible tannin levels and has opened up avenues for further research. What follows are the results of an experi- ment made from a single estate in two different vintages, with the objective to study the impact of geographic origin within French oak forests as well as grain width and potential tannin level of oak used in barrel making on the sen- sory profiles of red wines. The results indicated for barrels with the same geographic origin and grain width, a considerable variation of major oak aromatic compounds was attributable to the tannin potential of the wood, which in turn had a significant impact on the sensory profile. With this new analytical method of oak stave selec- tion and classification, winemakers are as- sured greater consistency and uniformity. However, this selection criterion must be combined with an automated toasting process capable of controlling thermal degradation of the oak tannin to achieve consistent and re- producible results. Impact of Oak Tannin on Red Wines Trial at first-growth château examines effects of geographic origin, grain and tannin on sensory profile By Marie-Laure Badet-Murat, Fréderic Desamais and Jean-Charles Vicard The challenge for winemakers is to obtain barrels of known, homogeneous, reproducible quality. Therefore, it is neces- sary for cooperages to control the concentration of extract- able compounds in oak.