Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
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July/August 2009
Impact of délestage with partial seed removal
fermentation.38 Polymeric flavan-3-ols, referred to as proanthocyanidins or condensed tannins, arise either by addition of intermediates from flavan-3,4-diols to flavan-3-ol monomers, or by acetaldehyde-induced polymerization.8,35
Grape seeds differ from skins in that seed proanthocyanidins contain greater levels of monomeric flavan-3-ols, and those esterified to gallic acid.5,25,32 Additionally, seed proanthocyanidins generally have a lower dp (degree of polymerization) than those found in skins, and no trihydroxylation of the Bring. 9Proanthocyanidins are reactivemolecules that may form complex species thought to impactwine sensory features.
Monomeric and polymeric flavan- 3-ols induce both astringent and bitter mouth sensations. S. Vidal et al. demonstrated that overall astringency increased with increases in dp.38 Additionally, they reported that galloylation increased tannin coarseness, while trihydroxylation of the B-ring decreased coarseness.
Bruce W. Zoecklein1*, Lisa M. Pélanne2, Sandy S. Birkenmaier3, Karen Reed4
Delestage élestage (rack and return) involving partial seed removal was compared with Merlot produced by manual cap punch down (three years), and Cabernet Sauvignon produced by mechanical punch-down (pigeage) systems (one year).
Fermentation reduced the color derived from monomeric pigments and increased polymeric pigment color for all treatments. Délestage wines generally had more large polymeric pigment color than cap-punched or pigeage wines. Total glycosides increased during cold soak and fermentation, and were in greater concentration in cap-punched Merlot, and similar among Cabernet Sauvignon treatments.
Discrimination testing (triangle difference analysis) demonstrated Merlot wines generally differed in aroma and/or flavor. Cabernet Sauvignon wines differed in both aroma and flavor.
The color, structure, and aftertaste of red wines are mainly derived from the varied and complex impact of phenolic compounds. It is estimated that 50% or less of the total phenolic compounds present in the skins, seeds, and flesh of grapes can be extracted during conventional winemaking.12,36
1 Professor and Head, Enology-Grape Chemistry Group
2,3 Research Associate/Laboratory Specialist, Enology-Grape Chemistry Group Virginia Tech, Blacksburg, VA
4 Viticulture Coordinator, Clos Pegase, Calistoga, CA
* Corresponding author [Fax: 540/231-9293; e-mail:]
The level of extraction depends on various factors, including fruit maturity, duration of skin contact, temperature, ethanol concentration,20 and vinification practices, including cap management techniques.7,16,22,31 Therefore, understanding the quantitative and qualitative influences processing has on grape and wine phenolic compounds is important in premium wine production.
Monomeric and polymeric flavan-3-ols comprise the majority of phenolic constituents in red wines,30 being extracted from the skins and outer seed coat during
Aeration across a screen with seed removal during draining of the fermentor.
Photo by Wendy Day, Vine Cliff Winery (Napa, CA).