Enology Notes

ENOLOGY NOTES # 4 September 27, 2000

To: Virginia Vintners and Prospective Vintners

From: Bruce Zoecklein

Subject: Aromas, flavors and color

This season has been difficult, yet the overall potential wine quality seems to be very good. Some have been surprised at the extent of varietal character at somewhat low Brix values. The relatively constant, intermediate temperatures we have had during ripening favor the biochemical processes that produce color and aroma/flavor compounds. These processes are capable of continuing 24 hours a day provided that sugar substrates are available and temperatures are favorable for enzyme activities. During most seasons, excessive day-time temperatures limit certain enzymatic reactions and, therefore, the production of secondary plant metabolites such as aroma/flavor and color compounds. Less variation about a mean or average ripening temperature results in greater aroma/flavor and pigment production. Indeed, many would agree that the best wine producing regions of Europe are characterized by relatively narrow ranges of day to day and day to night temperatures during ripening. As we have seen thus far this season, grapes can achieve desirable aroma/flavor and color at relatively low Brix and pH values with high acidity remaining.

With the acids higher than we frequently see in reds, it is essential that the fruit have mature skin and seed tannins to maximize structural balance. The relatively low pH values coupled with mature tannins allows the production of wines that are both supple and have some longevity. To help assure proper tannin evolution, keep the sulfur dioxide level in the fermenter relatively low. With a higher than desirable incidence of fruit rot there is a tendency to add more sulfur dioxide to the must than usual. The influence of sulfur dioxide on microorganisms at this stage is limited. Yet, additions greater than 25 mg/L can inhibit phenol polymerization, thus effecting tannin evolution, suppleness and stability.

As discussed at several roundtable meetings, the pre-fermentation addition of tannins to reds is a tool which can improve wine structure and mouth feel. This may be particularly justified this season with those reds which demonstrate good varietal aroma/flavor intensity. Pre-fermentation addition of tannin in the form of commercial tannins and /or wood can add more depth and structure. I have recommended the addition of wood to red wine fermentations. Fermentation with wood allows wood tannins to rapidly integrate into the wine, helping to add complexity while preserving >fruit=. It is the varietal fruit character which is often lost in our red wines as we attempt to gain complexity by barrel aging. As with tannins, there are several viable wood products on the market. You can purchase stave quality cubs, from specific sources, toasting levels, age etc.