Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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NOVEMBER/DECEMBER 2010
WINEMAKING
BY
Andrei Prida,1
Jessica Drinkine-Magneux,3
Regis Gougeon,2
David Chassagne2,3
1 - Tonnellerie Seguin Moreau, Z.I. Merpins, Cognac, France
2 - Institut Universitaire de la Vigne et du Vin “Jules Guyot,” E.A. 581 EMMA, Université de Bourgogne, Dijon, France
3 - CESEO (Cellule d’Expertise Scientifique en OEnologie), Institut Universitaire de la Vigne et du Vin “Jules Guyot ,” Université de Bourgogne, Dijon, France
B
Barrel ageing is a key stage in producing great wines. Two major phenomena occur during barrel ageing: one consists of oxidation of certain substances in wines due to oxygen penetrating into the barrel and the other is the diffusion of extractable compounds from oak wood into the wine. These substances modify the wine’s aromas and flavors, adding complexity and hints of “coconut,” “toast,” “vanilla” etc.3
PHOTO ABOVE: Volume in the water-immersion tank is changed every seven barrels, through continuous introduction of new water (de-chlorinated, filtered, and UV-sterilized), and removal of water charged with oak extractives. Each barrel spends less than one hour in the tank prior to fire-bending.
Photo (left): Barrel immersion in hot water prior to bending. Figure 1 (ABOVE): Barrel production process. A – bending following heating over a fire; B – bending following heating by immersion.
Once the extractable compounds from the wood have been released into the wine, they may be modified by chemical and enzyme reactions.7,9,10,11,2,4 Furthermore, the macromolecular structure of oak wood may absorb certain constituents from the wine.1,8 These phenomena result in marked organoleptic changes in the wine.
The complexity of barrel-ageing phenomena and their impact on wine quality make these containers valuable winemaking tools. Winemakers’ objectives change to suit market tastes. The current trend in the winemaking world is to make barrel-aged wines with complex, fruity flavors, and relatively discreet oakiness. This trend is most marked among independent winegrowers, who want their wines to express their terroir, rather than any “universal” taste.6
Some coopers use immersion in hot water to prepare the raised (assembling of the staves in the shape of the barrel before staves are bent and heads are inserted) barrels for bending, but this process is much less widespread than traditional heating over a wood fire.
The immersion method consists of soaking raised barrels in hot water, then bending the staves rapidly to form the barrel before it is
toasted. The only difference from the traditional process is that heating over a fire prior to bending is replaced by immersion in water, and then the process continues with toasting.
The first objective of this technique is to reduce stavewood breakage with water immersion before bending, to minimize the waste of broken oak staves occurring from bending following heating over an open fire.
However, this is by no means the most important aspect of the process. The adsorption of water by wood, extraction of wood components, and heat transfer in the wood-water system formed by immersing the barrel in hot water, then toasting wood with a high humidity level drive different kinetics in the production of compounds from toasting and degradation of wood compounds over fire from those that occur after traditional fire bending prior to toasting.
It is noteworthy that during traditional fire toasting coopers spray some water on the inside of the barrel in order to prepare the barrel for bending. However, contrary to water immersion, this operation does not allow any significant changes in wood composition, the moisture content remaining stable.
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