Practical Winery
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July/August 2009
Figure VI. Effect of pigeage and délestage on Cabernet Sauvignon — monomeric pigments (MP) as a percentage of total color during cold soak, fermentation, and post-fermentation; n = 3.
Due to logistical limitations, including the necessity for replications, wines were not produced by délestage alone, without seed removal.
The majority of the seeds removed (average 25%) were removed in the first few days of fermentation, possibly contributing to the lower total tannin concentration frequently observed in délestage-produced wines. Tannin levels generally remained stable in the must until active fermentation, then increased significantly.
V. Singleton and P. Draper demonstrated that fermentation for 90 hours resulted in extraction of 65% of the available seed tannins, while 180 hours resulted in the extraction of 70%.28 Seed tannins comprise approximately 60% of the total phenols in conventionallyproduced red wines,28 with nearly half of the extractable catechins and oligomeric proanthocyanidins in grape seeds transferred into wine.37
V. Kovac et al. added seeds during fermentation (6% of the weight of the fruit) and noted a doubling in the concentration of catechins and proanthocyanidins in the fermented wine.15 For the Merlot wines, about 1.1% of the weight of the fruit was removed as seeds during délestage. A. Bosso et al. compared pump over with délestage, using Montepulciano d`Abruzzo, and found that pump over produced wines higher in anthocyanins, polymeric pigments, and tannins.3
In the current study, délestage wines contained a lower tannin concentration than controls (manual cap punch down or pigeage), possibly due to limited extraction and seed removal in délestage treatments. However, HPLC analysis of aged wines did not demonstrate statistical differences in selected phenols, including those associated with seeds, such as catechin and epicatechin.
Phenol extraction from seeds is dependent, in part, on the degree of seed oxidation or maturity.9 Délestage can allow fermenting juice to percolate through the cap, providing an exchange that may minimize particulate extraction from the cap (Dominique Delteil, 2003, personal communication).
Although not measured in this study, it is possible that délestage reduced the concentration of non-soluble solids, thereby aiding in reduction of total phenols, including skin tannins. Total anthocyanins were frequently in greater concentrations in conventional- and pigeage-produced wines, compared to délestage, possibly suggesting greater extraction.
The higher concentration of total glycosides noted in manual cappunched Merlot wines may also indicate increased extraction, although there were no differences in total glycosides in the Cabernet Sauvignon produced by pigeage and délestage.
Formation of polymeric pigments is important due to their contribution to color stability. It has been demonstrated that, after only a few years of ageing, the vastmajority of color is due to polymeric pigments, with a small concentration of monomeric anthocyanins remaining.33
Analysis of the fruit demonstrated a relatively high percentage of color from monomeric pigments compared to LPP, consistent with D.Adams et al.,2 and J. Harbertson et al.11
In the second and third years, the Merlot fruit LPP averaged 9.8% of the color, while corresponding wines averaged 18.5% color from LPP. The increase in percentage of wine color from LPP, comparedto the fruit, appearedto parallel a decrease in the percentage of color from monomeric anthocyanins in thewine.
It is generally assumed that formation of polymeric pigments is the result of relatively slow, post-fermentation reactions.34 J. Eglinton et al. however, demonstrated that fermenting yeast cells and their metabolites are actively involved in condensation reactions with tannins and anthocyanins, suggesting polymeric pigment formation during fermentation.6
In this study, it must be noted that the analyses of the percentage of color fromMP, SPP, and LPP are estimations. For example, while not impacted by the phenolic matrix,11 monomeric anthocyanins at the pH of the assay are largely in the leuco- or colorless form.
The percentage of Cabernet Sauvignon color from monomeric pigments declined during fermentation for both treatments, by an average of 25%. A. Zimman and A. Waterhouse demonstrated that a significant percentage of the loss of monomeric pigments could be due to association with grape solids.42 Therefore, it is possible that a cap management technique that impacts the non-soluble solids level could impactmonomeric anthocyanins.