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
Key: sens. = sensory analysis; chem. = chemical analysis; AF = alcoholic fermentation, MLF = malolactic fermentation
Panelists performed blind quantitative descriptive analysis using a standard list of descriptors including six odor (overall oaky, fruity, sawdust, vanilla, toasty, spicy) and five taste descriptors (acidity, bitterness, tannic intensity, structure, length). The sensory sessions were organized by series with the same wine aged in fire-bent and immersion/fire-bent barrels. The order of presentation was arbitrary and different for different panelists to obtain more objective data.
The tasting sessions were conducted in tasting rooms following the usual practices in wine tasting and were conducted by a session observer. Before the sensory analysis, the bottle was tasted in order to look for possible off-flavors and was rejected if there was an abnormal odor.
Panel members awarded 0 to 10 points according to the intensity of each descriptor (0 – very weak, 10 – very strong).
The values given by each taster were normalized using the average value for that taster over the entire series. The Independent Student’s T-test was applied to the normalized values to identify the descriptors for which there was a variation in intensity between the barrels made using “immersion” and the “traditional process.”
Only those descriptors showing differences with a probability below 5% were retained for further processing.
Analysis of volatile compounds
The following 19 odoriferous volatile molecules from oak wood were assayed in the wines using GC-MS:3
• furan and pyran compounds (furfural, 5-hydroxymethyl-furfural, 5-methyl-furfural, furfuryl alcohol, maltol, and ethyl maltol) – class of compounds characterized by toasty and butterscotch odors in pure state;
• aromatic aldehydes (vanillin and syringaldehyde) – class of compounds characterized by vanilla/woody odors in pure state;
• volatile phenols (guaiacol, 4-methyl-guaiacol, eugenol, isoeugenol, o-cresol, m-cresol, phenol, syringol, and allylsyringol) – class of compounds characterized by smoky, phenol and spicy odors in pure state;
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Wines aged in barrels where the staves have been bent following hot water immersion are empirically perceived to be less marked by oaky aromas. However, to date, very little scientific data was available concerning the impact of this bending technique on wood/wine exchanges, thus making it impossible to explain the sensory differences noted in empirical observations.
This report presents the results of a two-year comparative study of the two stave bending techniques, focusing on the sensory profiles of wines aged in the different types of barrels and their concentrations of volatile molecules.
Material and methods
Barrel production
The barrels were made by Tonnellerie Seguin Moreau (Seguin Moreau Burgundy ZAC du Pré Fleury les Creusottes Nord, Chagny, France) using staves bent either following immersion or by heating over a fire (see Figure 1). All barrels were produced from one batch of French fine grain oak.
In the “traditional process,” raised barrels are preheated (A) for 10 to 15 minutes to a temperature of 100° to 120°C to soften the wood fibers and make them pliable. This process does not cause any major production of compounds arising from toasting; indeed,
any modifications are insignificant compared to those that occur during the toasting stage.
In the process employing bending by “immersion,” the preheating stage (A) is replaced by soaking in hot water (B). The temperature of the water does not exceed 100°C; production of toasting products due to heating are negligible.
Toasting – The heating process that causes chemical modifications in the wood was performed according to the standard “medium-long” protocol used in the cooperage. This stage was identical, irrespective of the type of bending process: heating over a fire or by immersion.
Wines
Trials occurred on nine sites with nine wines (three white wines and six red wines) from two different vintages: 2007/2008 (Table I). Wines were either barrel-fermented or put into barrel before or after malolactic fermentation. There were three barrels in each wine lot.
Sensory analysis
Sensory analysis by a tasting panel of Seguin Moreau staff (panel I of 8 to 14 persons), and a trained panel of enology students from the Institut Universitaire de la Vigne et du Vin (panel II of 16 to 18 persons), was done at regular intervals, as described in Table I.