To: Regional Wine Producers

From: Bruce Zoecklein, Head, Enology-Grape Chemistry Group, Virginia Tech

Subject: VVA Winter Meeting; Wine Balance

VVA Winter Meeting. The winter meeting of the Virginia Vineyards Association is February 13-15 at the Omni Hotel Charlottesville, VA. Program and registration information is available from the VVA web site at: www.virginiavineyardsassociation.com.

The enology portion of the program is scheduled for Saturday, February 15. The theme is “The Synergy of Wine Structure and Flavor”.

The program outline is as follows: most presentations will be accompanied by sensory evaluations.

Saturday Enology Program VVA Meeting 2003

Enology Session Introductory Remarks B. Zoecklein, Virginia Tech. Overview of the enology program and sensory evaluation format.

Grape and Wine Production in Uruguay Francisco Carrau, Faculty, University of the Republic, Montevideo, Uruguay. Overview of the grape and wine industry of Uruguay and parallels to Virginia’s.

Effects of Aroma/Flavor Trapping on Chardonnay Wine Quality Emily Hodson, Virginia Tech. Update on this practical method of adding back aroma/flavor volatiles, lost during fermentation, to increase wine quality.

Phenol Management Techniques in Virginia Vineyards and Wineries B. Zoecklein, Virginia Tech. Research information and practical discussion on the viticultural and enological issues effecting development, extraction and management of grape and wood-derived phenol compounds, and their relationships to wine quality.

Panel Presentation & Sensory Evaluation of Phenolic Management Techniques. Moderator, Bruce Zoecklein, Virginia Tech. Sensory evaluation and discussion of applied research trials conducted at two Virginia wineries.

Dave Collins, Winemaker, Breaux Vineyards Cap punching vs. deléstage of Cabernet Sauvignon

Michael Shaps, Partner and Winemaker, King Family Vineyards Short vs. long vatting of Merlot

France Study Tour Pascal Durand, University of Burgundy. A discussion of the recently concluded study tour to Southwest France, and possible future tours.

Technology of Tannat Production Francisco Carrau, Faculty, University of the Republic, Montevideo, Uruguay. A discussion regarding the production of this important red variety, including a sensory evaluation.

Effects of Alcohol on Wine Aroma/Flavor K.C. Fugelsang, Professor, California State University Fresno. A discussion on the impact of alcohol concentration on wine aroma/flavor and structural features and methods of dealcoholization. Five Syrah wines produced from the same fruit and dealcoholized to different levels will be evaluated.

As a prelude to this event, the following is a two-part review of some issues regarding wine structure and flavor.

Wine Balance. Palate balance is a critical feature influencing wine quality, by impacting the harmony and integration of structural components. The major factors governing palate balance in dry wines are the quantity and “quality” of tannins, concentration of alcohol, and concentration and types of acidity. These components interrelate, influencing the perception of balance according to the following:

Sweet » acidity + bitterness and astringency

The perception of sweetness derived from alcohol, polysaccharides and sugar (when present), must be in balance with the sum of the perceptions of acidity, astringency, and bitterness. This relationship suggests that the lower the acidity, the more tannin a wine can support. The palate balance formula is functionally analogous to the suppleness index described by Peynaud (1984):

Suppleness index = alcohol (vol/vol) -
(titratable acidity + tannin)

Red wines are not considered supple unless the suppleness index is below 5.0 (note that the acidity calculation uses sulfuric acid equivalents vs. tartartic acid) . The palate balance relationship is important in both maturity assessments and processing.

Phenolic Components and Balance. Some vineyards harvest fruits from each side of the grapevine canopy at different time periods. Why? The effects of light and temperature on phenols, among other things, can be significant. During the summer, the sun is in the southern part of the sky. Vineyard row orientation and canopy management can influence both heat and light into the canopy. For example, fruit on the southern side of east-west rows receives more light and heat.

Heat and light interception can have an important influence on fruit chemistry as we and others have seen. Based solely on the side of the canopy, we have noted a 31% difference in skin tannin per berry. We have also noted differences in skin pigment components: a 13% difference in total skin color per berry, and a 43% difference in the concentration of small polymeric pigments (SPP) in the skins (small molecular weight tannins associated with anthocyanins). These changes have been noted in the absence of differences in degrees Brix.

With regard to balance, both the quantity and quality of phenols is important. Chemically, grape and wine tannins are composed of subgroups (flavon-3-ols). In simplistic terms, those tannins which contain fewer than five subgroups are predominantly bitter and contribute to tannin hardness. Those tannins which contain more than five are predominantly astringent and contribute to suppleness. Robichaud and Noble (1990) found that both bitterness and astringency increased with increased concentration of (+)-catechin (tannin building blocks), although the rate of bitterness increase was greater than that of astringency.

On a per weight basis, both bitterness and astringency increase with increased degree of polymerization, but astringency increases at a greater rate. As polymerization increases, the number of possible hydrogen bonding sites increases, which would be expected to increase astringency.

Bitterness is the result of access to membrane-bound receptors, and is likely limited by molecular size. Differences in the lipid solubility of small molecular weight phenols allows them to depolarize the taste receptor cells, thus increasing the perception of bitterness. As grape skins mature, the average number of subunits in the tannins increases, increasing tannin suppleness. This is an important sensory and maturity feature.

The difficulties in assessing bitterness and astringency of various phenolic compounds involve the fact that astringency masks bitterness. As wines age, tannin polymerization and, possibly, precipitation occurs. This, coupled with the reduction of tannin astringency resulting from protein fining agents, for example, may slowly unmask bitterness.

Mature tannins in the fruit are a requirement for premium red wines and, therefore, are an important harvest consideration. If the skin contains non-polymerized, harsh tannins, so will the wine.

Subscription to Enology Notes. All past Enology Notes and Vintner's Corner newsjournals are posted on the Enology-Grape Chemistry Group's web site at: http://www.fst.vt.edu/zoecklein/index.html or http://www.vtwines.info/. Enology Notes are slightly different in content from the subscription based Vintner's Corner newsjournal.

To be added to the Enology Notes list serve send an email message to bzoeckle@vt.edu with the word "ADD" or "REMOVE" in the subject line.

Dr. Bruce Zoecklein
Associate 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: www.vtwines.info or www.fst.vt.edu/zoecklein/index.html
Phone: (540) 231-5325
Fax: (540) 231-9293
Email: bzoeckle@vt.edu