Vol.17, No. 5 September - October, 2002
Bruce W. Zoecklein
Department of Food Science and Technology
VPI & SU - 0418
Blacksburg, VA 24061
Web site: http://www.vtwines.info/
Table of Contents
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I. Aroma and Flavor Integration Considerations
Lees contact has been traditionally a production component in Burgundian style Chardonnay. Lees contact contributes to the complexity of the wine by the integration of yeast characteristics with fruit and wood flavors. Lees management is, therefore, an important aroma and flavor consideration. Lees nourish the wine during aging, imparting aromas and structure, by filling out the body and adding depth, length and complexity. Table 1 shows some important considerations regarding lees management.
- NON-SOLUBLE SOLIDS LEVEL
- METHOD OF STIRRING
- FREQUENCY AND DURATION OF STIRRING
- TYPE AND SIZE OF VESSEL
- DURATION OF LEES CONTACT
- TIMING AND TYPE OF RACKING
- SO2 TIMING AND LEVEL OF ADDITION
- FREQUENCY OF BARREL TOPPING
During lees contact, the composition of the wine changes as the yeast commence enzymatic hydrolysis of their intracellular constituents. One important feature is the process of proteolysis, whereby proteins are hydrolyzed to amino acids and peptides. These compounds result in an increase in the nitrogen content of the wine. It is known that amino acids can act as flavor precursors, possibly enhancing wine complexity and quality.
During sur lie storage, yeast components such as cell wall polysaccharides, and particularly mannoproteins, are released into the wine. These macromolecules can positively influence structural integration, phenols (including tannins), body, aroma, oxygen buffering and wine stability. The interest in lees utilization goes beyond barrel-fermented Chardonnay. As has been discussed in other issues, sur lie storage is becoming much more important in red wine production.
Yeast-derived macromolecules provide a sense of sweetness as a result of binding with wood phenols and organic acids, aiding in the harmony of a wine's structural elements by softening tannins.
As discussed during the pre-harvest workshop, it is important to differentiate between light lees and heavy lees.
Heavy lees can be defined as the lees which precipitate within 24 hours immediately post-fermentation. They are composed of large particles (greater than 100 microns) and consist of vegetable particles, agglomerates of tartrate crystals, yeasts, bacteria, and protein-polysaccharide-tannin complexes (Delteil, 2002).
Light lees, on the other hand, can be defined as those that precipitate from the wine more than 24 hours post-fermentation. These are composed mainly of small particles (1-25 microns) of yeasts, bacteria, tartaric acid, protein-tannin complexes and some polysaccharides (Delteil, 2002).
There is no value in storing wine on heavy lees. Indeed, such storage can result in off aroma and flavors, and a depletion of sulfur dioxide.
Light lees storage, however, can have a significant advantage in structural balance, complexity and stability.
Lees stirring and the frequency of stirring is important, both as a practical and stylistic consideration. Stirring generates an oxidative process which increases the acetaldehyde content and which may increase the acetic acid concentration. Stirring also changes the sensory balance between fruit, yeast and wood by enhancing the yeast component, reducing the fruit, and, to a lesser degree, the wood component. Additionally, stirring may have the effect of enhancing secondary chemical reactions, possibly as the result of oxygen pick-up. Stuckey et al. (1991) demonstrated increases in both the total amino acid content and wine sensory score in wines stored for five months without stirring. The non-stirred wine was perceived to have greater fruit intensity.
MLF reduces the harshness of new oak and aids in the development of complex and mature flavors. Traditionally, stirring is continued until MLF is complete. After that, the lees are said to become more dense, so as to aid in clarification.
During barrel aging what we are looking for is slow, well-managed, and controlled oxygenation. Lees allow for this oxygenation and they aid in the prevention of oxidation. Traditionally in Burgundy, wines are racked off the lees in March, usually the time when MLF is completed. Frequently this is an aerobic racking off the heavy lees, then back into wood on light lees, followed by an SO2 addition. Leaving the wine on the light lees helps to nourish the wine. The addition of SO2 helps to protect the wine from oxidation. A subsequent racking often occurs in early July and is in the absence of air. Timing of SO2 additions, and the quantity of SO2 added, are important stylistic considerations. Early use of SO2 increases the number of components that bind subsequent additions of SO2. The addition of too much SO2 counters the wood flavors and limits oxidation reactions, while too little SO2 may allow the wine to become tired and overaged. Production considerations, such as the method of barrel storage and time of bottling, are factors influencing SO2 levels. Barrel topping is an aerobic process that can result in excessive oxidation. Additionally, wines that spend a second winter in the cellar tend to lose their aroma unless the wine is particularly rich.
If fruit such as strawberries or apples are made into wines, the public expects them to have the flavor of fresh fruit. Fortunately, no such expectations apply to grape wines, partly because few consumers have any preconceived notions regarding wine grape flavors. This allows for a broad degree of stylistic freedom. What the public does expect, however, is a well-balanced wine, one that possesses a whole symphony of integrated flavors and aromas. To produce such a wine requires an understanding of the grape and how each processing variable influences the balance of fruit, wood, bacterial and yeast aroma, and flavor notes.
At both the Norton Winemakers Roundtable and the Pre-Harvest Workshop, I shared some data from Delteil (2002) who compared two red wines. One red wine was barrel stored on light lees for 9 months; the other, racked several times prior to barreling, was stored for the same period without lees. These two Syrah wines differed significantly in their palate and aroma profiles.
The wine stored sur lie had a much lower perception of astringency and a greater integration of the phenolic elements. The sur lie wine also had a lower perception of oak character, resulting in a higher perception of varietal fruit.
II. Upcoming Events
France Study Tour. December 4-17th. This tour is full. Those who are registered will receive tickets and complete itinerary within the next several weeks.
Juice and Wine Analysis Short Course. Food Science and Technology Bldg., Virginia Tech, January 7 and 8, 2003. Fee $350. Information online at www.vtwines.info and see below.
Special Topics in Tannin-Color Measurement and Management Short Course. Food Science and Technology Bldg., Virginia Tech. January 16, 2003. Pre-registration required. Fee $200. Information and registration will be posted on-line at www.vtwines.info and be mailed via Enology Notes. Only 14 slots are available. Virginia producers will get priority until November 15, 2002.
Virginia Vineyards Association Annual Meeting. February 13-16, 2002. This meeting will have an increased number of enology-oriented programs. Further details will be posted online.
Juice and Wine Analysis Short Course. The Enology-Grape Chemistry Group will offer a two-day juice and wine analysis short course on January 7 and 8, 2003. This program will be a hands-on, practically oriented laboratory course. It will be conducted in the teaching laboratory of the Food Science and Technology Building at Virginia Tech.
This program will include the following:
Registrants will participate in hands-on analysis. Analysis will be supplemented with a laboratory manual and discussions concerning the practical winemaking significance of each test.
Enrollment is Limited: The short course will be limited to a total of 14 participants. Only one person per bonded winery may register. You must register for both days. Registration preference will be given to Virginia bonded winery representatives that register BEFORE FRIDAY, NOVEMBER 1, 2002. After that date, open enrollment will be offered if space is available. Preference will be given to those already in the commercial wine industry.
You will not be registered until your check is received!!!
Cost: $350 per person, due by November 1, 2002, checks payable to:
Bruce Zoecklein, Foundation Account, Virginia Tech.
Head, Enology-Grape Chemistry Group
Department of Food Science & Technology
Virginia Tech - 0418
Blacksburg, VA 24061
Course fee is non-refundable.
III. Virginia Wine Guide
The Virginia Wine Guide is a relatively new independent online consumer's guide to Virginia wines. It offers expert ratings and reviews. Check it out at: www.Virginiawineguide.com.
IV. Budget Reductions
For the current fiscal year we have experienced a 15% budget cut. In mid-October the Governor will announce the next round of budget reductions for higher education. Our College of Agriculture and Life Sciences will experience another 9, 11 or 15% budget reduction. State-wide it is estimated that higher education will lose as many as 7,000 personnel.
If you would like to have your name added or removed from our list serve for future Enology Notes, please send a blank e-mail to email@example.com with the word "Add" or "Remove" in the subject line.