To: Regional Wine Producers
From: Bruce Zoecklein, Head, Wine/Enology-Grape Group, Virginia Tech.
This issue of Enology Notes continues the discussion from #84 regarding management of red wine structural balance and mouthfeel. Post-fermentation options include biological and non-biological deacidification, fining, addition of modifying agents such as gum arabic, thermal processing, microoxygenation, and sur-lie storage. Limiting new oak exposure and Brettanomyces growth may also be important in optimizing red wine mouthfeel and balance.
Yeast fining: Traditionally, yeast fining has involved the addition of hydrated yeasts used as adsorption agents. Consisting of approximately 30% protein, yeast cell walls may play an important role in the complexing with wine components, such as polyphenols and metals. Indeed, yeast fining is a practical means of removing excess copper (greater than 0.5 mg/L) when copper is used to bind selected VSCs (volatile sulfur compounds, see Enology Notes # 70).
We have conducted a number of trials evaluating the effects of yeast fining as a method of improving red wine mouthfeel. The primary basis for these evaluations is that yeast can liberate polysaccharides, that can impact phenols, and thus mouthfeel. Polysaccharides are present in the outside envelope of the yeast wall. Different yeast strains release different concentrations of polysaccharides, most likely due to differences in enzyme (glucanase) activity. Polysaccharides can add roundness and body to wines.
The Wine/Enology-Grape Chemistry Group has conducted several trials, using red wines of different varietal make-up and age. Several high polysaccharide-producing yeast strains were evaluated, by adding 1 g/L of yeast, post-fermentation, directly, without hydration, to each wine. Treatment replication and control wines were mixed once per week for three weeks, racked off the yeast, and evaluated chemically and sensorially to determine the impact on color, aroma/flavor, and mouthfeel. The main goal of this study was to determine if yeast fining, as described, would be a practical way of improving the structural balance and mouthfeel of our 2003 red wines. Because of the nature of the season, many of our reds need modification.
The impact of yeast fining on red wine color components (expressed in AU, or absorption units) is given in Figures 1, 2, and 3 (NS stands for non significance; * stands for significance at 0.05 level). Fining, including yeast fining, can remove color. The extent of color removal depends on a number of factors, including the age of the wine.
Red wine color attributes are influenced by the three parameters measured in these figures: total anthocyanins, copigmented anthocyanins, and polymerized pigments. Each is strongly impacted by viticultural and environmental factors, while the effect of processing is less clear.
It is estimated that 30-50% of the spectral color in a red wine is the result of copigmentation, pigmented molecules and colorless phenols stacked to form colored aggregates. The ability to create copigments is the main difference among red cultivars, not the concentration of anthocyanins (Boulton, 2001). For example, an average Cabernet Sauvignon with 360 mg/L total anthocyanins could have 17% of these anthocyanins in the copigmented form. Yet, 40% of the total visual red color of the wine comes from those copigmented anthocyanins.
As stated, wines of different ages were used, due to the relative difference in the ratio of free anthocyanins to the polymeric forms. The greatest effect on the free anthocyanins, not unexpectedly, occurred with the 2003 Cab Franc. Young wines have the highest percentage of free or monomeric anthocyanins. The effect of yeast fining on copigmented anthocyanins was not always statistically significant, but fairly large. This represents a possible disadvantage to this treatment. Figure 3 demonstrates the impact on polymeric pigments. Yeast cells have a limited ability to bind with larger molecular weight compounds, as demonstrated.
The true advantage of yeast fining is the softening effect on phenols, and the increase in body. All the yeast fining trials demonstrated that impact. As discussed in Enology Notes #84, the softening of the tannin intensity also lowers the perception of the acidity, thus increasing the perception of volume or body.
It is also logical that yeast fining impacts wine odor, and it did so in these trials. Esters and other cell wall components are liberated from yeasts during yeast fining. The fatty acid esters, such as ethyl hexanoate and ethyl octanoate, can provide sweet and spicy aromas. The 2003 Cabernet Franc control wines had some varietal expression, but were dominated by an herbal element, which unbalanced the wine. The yeast fining trials had the greatest impact on the aromatic characteristics of the 2003, reducing the herbaceousness, thereby increasing the berry fruit intensity. The impact of yeast fining on the other wines in this study could be described as variable, but with a general increase in complexity. Details of our analysis of aroma volatiles will be shared in subsequent editions.
This study suggests the possible viability of using yeast fining for modification of wines, particularly from our 2003 season. Because each wine's response will vary, it is essential that fining trials be established and carefully reviewed prior to cellar treatment (see Zoecklein et al., 1999).
2. American Society for Enology and Viticulture Annual Meeting and International Symposium. The American Society for Enology and Viticulture will hold its technical meeting and symposium July 14-16, 2004, at the Hotel Roanoke and Conference Center, Roanoke, VA.
The symposium associated with the meeting is titled Grapes, Wine and the Environment. The goal is to explore how soils, climate (particularly temperature), and cultural practices affect fruit and wine composition and quality. Keynote speakers include the following.
Zelema Long of Zelphi Wines, California, will begin this symposium by defining climate indices for understanding of wine quality. What is a cool vs. warm climate, and what does that really mean?
Kees van Leeuwen, winemaker of Cheval Blanc, Bordeaux, will discuss the concept of terroir and the production of high-quality wines, and the effects of soil on vine-water relationships
Erland Happ, winemaker for Happs and Three Hills Winery, Western Australia, will discuss the concept of heat indexing to categorize site climates. Heat indexing will be correlated to cultivar and wine quality.
Gregory Jones, Department of Geography at Southern Oregon University, will provide an overview of global climate and wine quality relationships, and an analysis of how region can impact wine quality, using Bordeaux as an example. He will also present how local climate databases can be used to predict grape-growing and winemaking potential.
Andy Reynolds, Research Chair in Viticulture, Brock University's Cool Climate Oenology and Viticulture Institute, will review the goals and results of various canopy management practices, specifically for aroma, flavor and color synthesis, and will contrast cool vs. warm climates.
Phillip Freese, of WineGrow and Zelphi Wines, will discuss improving mouthfeel in the vineyard, factors impacting skin and seed phenol development.
Daniel Granes, Research Director, ICV, Narbonne, France, will present methods of conducting alcoholic fermentation, and oak management to develop grape potential in warm climates.
Bruce Zoecklein will discuss the use of Delestage with seed deportation as a fermentation management tool, and Tony Wolf will present research on training systems and fruit composition.
Mark your calendars! Additional information will be posted on my website and the ASEV-ES site at www.nysaes.cornell.edu/fst/asev.
3. Research Activity. Beginning in January, I will be working in Virginia, California, and France. For Virginia wineries requesting lab analysis, it will be business as usual. I will be available via email and voice mail, and Enology Notes will continue to be sent.
Subscription to Enology Notes. All past Enology Notes newsjournals are posted on the Enology-Grape Chemistry Group's web site at: http://www.vtwines.info/. Enology Notes are slightly different in content from the subscription based Vintner's Corner newsjournal.
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Professor and Enology Specialist Head Enology-Grape Chemistry Group
Department of Food Science and Technology, Virginia Tech
Blacksburg VA 24061
Enology-Grape Chemistry Group Web address: http://www.vtwines.info/
Phone: (540) 231-5325
Fax: (540) 231-9293