Enology Notes

Enology Notes #63, October 30, 2002

To: Regional Wine Producers

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

Subject: Aroma/Flavor and the 2002 Season; Organic Grape Growing; Enology Notes and Vintner's Corner On-Line; Custom Crush.

Aroma/Flavor and the 2002 Season. One measure of the quality of the 2002 vintage is aroma/flavor, and the intensity or depth of aroma/flavor.

Our aroma/flavor research has involved the evaluation of free grape volatiles and bound aroma/flavor precursors.

Considering the disparate origins of the many members of these groups, and the multiple enzyme systems that are needed for synthesis and transformation, it is expected that large variation would occur in the formation and accumulation of individual aroma/flavor constituents.

Temperature (before and during the last month of ripening) and light govern the plant enzyme systems which regulate grape aroma/flavor compounds. Unfortunately, the impact of heat and light is not well understood and, naturally, these vary tremendously among seasons and sites.

Temperature is a primary influence of macro-, meso- and micro-climate. Seasonal temperature variations have a strong influence on aroma/flavor compounds, as do trellis system and canopy management. Because canopy climate is influenced by the grower, this is particularly important in influencing wine style.

Unfortunately, in warm climate regions, there is a fairly narrow range between too little and too much light exposure and heat, for optimizing aroma/flavor compounds.

In most warm climatic regions, including our own, the time between fruit set and a given fruit Brix, for example, can vary significantly from one season to another. Our research suggests an important trend. Under the climatic conditions of Virginia, the slower the speed of ripening, the lower is the concentration of all classes of glycosidically-bound aroma/flavor precursors. Details regarding this research are posted on the Enology Grape Chemistry Group website (Effect of crop load on aroma/flavor precursors). From extension, click on-line publications.

The speed of fruit ripening is influenced by environmental conditions, among other things. Crop level (exposed leaf area per gram of fruit) as we have seen, can also have a large impact. This includes fruit per vine, as well as the number of clusters per shoot. Research indicates that the aroma/flavor potential is enhanced by single vs. multiple clusters per shoot.

Our research generally demonstrates a strong inverse correlation between malic acid (and, to a lesser degree, TA) and bound aroma/flavor compounds. The greater the rate of malic acid respiration, the greater the concentrations of all classes of grape glycosides, those bound compounds representing, in part, a pool of potential aroma/flavor.

There are exceptions which confound the above relationship. Vines under water stress, such as occurred in various vineyards this season, have fruit which can ripen quickly. Here there appears to be an imbalance between formation of aroma/flavor components and preservation.

The importance of fine tuning canopy management, to optimize heat and light for maximizing aroma/flavor, is becoming increasingly evident. This is a reason for differential fruit zone leaf removal depending upon cultivar, style, training system, canopy side, row orientation, trellis height and spacing.

How did heat and light impact the aroma/flavor compounds in your fruit this season? How were they different from previous years? What is the optimum degree of fruit exposure for your wine quality and styles? What are you doing to answer these questions?

Organic Grape Growing. With the new organic food labeling laws recently enacted, the discussion about organic grape growing has been rekindled. California has more that 6,800 acres of vineyards being farmed organically, only about 2% of the state's total. However, with vineyards being increasingly surrounded by residential areas, community concern about the environment, and what is in and on our foods, the number of organic vineyards will likely increase.

Producers in California who use certified organic fruit, and adhere to minimal use of sulfur dioxide, will be able to label their wines "made from organic grapes", similar to standards used by some French houses.

This trend is here to stay, as evidenced by the California Wine Institute's unveiling of the Code of Sustainable Winegrowing Practices.

What does all this mean for growers and winemakers in our region? At the least, an increase in consumer awareness. Now, more than ever, it is essential that each winery have in place a viticultural HACCP (hazard analysis and critical control point)-like plan, which reviews all aspects of vineyard spray use including, and particularly for independent growers.

For information on establishment of a viticulture HACCP-like plan, see Enology Note #8. Additional discussions regarding HACCP are also available in Enology Notes # 22, 24, 52 and 59.

Enology Notes. All previous Enology Notes and Vintners Corner hard copy newsjournals are available on-line at www.vtwines.info.

Custom Crush. In November of 2001, I provided a proposed legislative change to the Virginia Wineries Association, which would permit custom processing. Apparently, this subject will be discussed at the upcoming Association meeting. Those interested in viewing this submission or understanding the North Carolina regulations on this topic can go to www.vtwines.info, click extension, and then on-line publications.

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