NEXT PHASE OF STUDY - RESULTS WITH WINE
A follow-up study has just been completed, with the generous cooperation of Lafond Winery and Edna Valley Vineyards. Many of the barrels used in the "water rinse" study were employed in aging wines (Chardonnay and Pinot Noir) in a systematic manner. The wines have been analysed for the same oak aroma compounds, and these results have been compared to the original study. We were interested to determine the correlation, if any, between the water extracted compounds and their presence in wine.
The following observations, contributed by Eric Herve, PhD (ETS Laboratories), may be useful to understand the data collected and expressed as graphs.
CHARDONNAY (experiment conducted at Edna Valley Vineyards)
Comparison of water vs. wine extraction: (Figure 8)
Note: the barrels used were all medium toast. The water rinses predicted the general shapes of charts obtained for wines, from the barrels appearing more toasted (Damy) to those appearing less toasted (Other). On the other hand, final concentrations of aroma compounds in wines aged in the 'Other' Burgundy cooper's barrels are less than expected, while (relatively) more than expected with the Damy barrels. The compounds for which the prediction is less accurate are aldehydes (Vanillin, Furfural and 5 methylFurfural). Note that final concentrations of those compounds can be strongly influenced by yeast metabolism (reduction to non-odorant alcohols during the alcoholic fermentation).
Wine comparison at 3 month vs. 7 months: (Figure 9)
Concentrations for all compounds increased in similar proportions (20% to 40%), with charts obtained showing almost identical shapes and sizes. Interestingly, final concentrations of Furfural in both the Damy and Billon barrels are sufficiently high for this compound to participate directly in wine aroma (odour threshold for Furfural: 15 000 ug/L in a model wine. source: P.Chatonnet).
PINOT NOIR (experiment conducted at Lafond Winery)
Comparison of water vs. wine extraction: (Figure 10)
Note: the barrels used were all M+ toast. The similarity of the charts obtained for water extracts compared to wines is quite striking. Despite the use of a different solvent (water only) and the extremely short contact time with wood, the profiles obtained with wines are accurately predicted. The discrepancies observed for Chardonnay do not appear here. The fact that the Pinot Noir wines were barrelled after the alcoholic fermentation, therefore minimising possible interactions of aroma compounds with yeasts, is a likely explanation.
Wine comparison at 3 month vs. 7 months: (Figure 11)
The increase for Furfural and 5methylFurfural (5MeF) is striking (10 fold increase!), while the increase for other compounds is similar to what is observed with Chardonnay wines. This is most likely a consequence of cross-linking reactions with tannins and anthocyanins. Some background: Moutounet's group (Montpellier) demonstrated that acetaldehyde and other aldehydes bind with tannin and anthocyanins, resulting in the formation of polymers that do not easily precipitate, hence stabilizing the structure and color of red wines. Cheynier's group also showed that polymers involving Furfural and 5MeF are even more stable than those made with acetaldehyde. This cross-linking of Furfural and 5MeF with polyphenols is a very interesting (and useful) interaction of wood with wine. This property would also explain levels observed for Furfural and 5MeF in the various wines in this experiment. Intermediate levels in Pinot Noir would be caused by its relatively low content of polyphenols (low for a red variety). During this trial, it is likely that Furfural and 5MeF extracted during the first months of aging cross-linked with Pinot Noir polyphenols, but that the process stopped at some point, allowing a dramatic increase of levels in wine, as seen after 7 months.
We have compared water-extracted compounds and those present in wine samples at different intervals, and observed that their correlation is not consistent in all instances. With Pinot Noir, the water rinse did accurately predict the compounds extracted by wines, although with chardonnay it did not. However, we suggest that discernable toasting styles can be revealed or validated in these types of studies.
SEE ALSO: PHASE 1 - Cooper Comparisons study.
Bouchard Cooperages wishes to thank:
- Gordon Burns, PhD and Eric Hervé, PhD (ETS Laboratories) for assistance in experimental design and analytical services.
- John Montero (Winemaking Consultant) for design and supervision of the study.
- C-Line Warehouse for providing space and personnel.
We also wish to thank the following winemakers, who provided indispensable and generous support of this portion of the study:
- Harry Hansen at Edna Valley Vineyards (San Luis Obispo, CA)
- Bruce McGuire at Lafond Winery (Buellton, CA)
© 2003, Vincent Bouchard