Enology Notes

Enology Notes #29 October 1, 2001

To: Virginia Vintners

From: Bruce Zoecklein

Subject: Enhancing Varietal Aroma/Flavor Intensity

Enzymes. Secondary plant metabolites provide varietal character in wine. The vast majority of grape-derived aroma potential is tied-up in conjugated forms, bound to complex sugars. Activities which hydrolyze or break the
sugar bonds of the conjugates can release free volatiles which may increase varietal character.

The addition of pectinolytic enzymes as a pre-fermentation settling aid for white juice can result in some conjugate hydrolysis, releasing free aroma volatiles. Most pectic enzymes have some b-glucosidase activity, which can cause conjugate hydrolysis. The aroma enhancing portion of the enzyme fraction is inhibited by the high sugar concentration, as found in juice. It appears that some of the enzyme survives fermentation and can react in the dry wine. Some enzyme producers suggest the addition of the enzymes with the yeast, as a means of increasing varietal character of red wines. There is evidence that wines produced from juice or must treated with enzymes can have more intense and complex aromas (Gunata et al., 1994).

Post-fermentation addition of pectic enzymes, or the so-called flavor enhancing enzymes, to dry wines may be a viable means of increasing the varietal intensity. These enzymes have the greatest impact on high terpene whites, such as Riesling, Gewurztraminer and Muscats. Note that these enzymes are not too specific in their hydrolysis and can release bound phenols, possibly increasing the perception of bitterness and/or astringency.

Enzymatic reactions activated by grape enzymes are involved in cell wall degradations and the release of vacuole contents when fruit is crushed. Commercial enzyme preparations containing pectinases, cellulases, and hemicellulases have been developed to increase these activities. These so-called maceration enzymes favor the release of cell wall skin tannins, and can add more fullness and red wine body.

Enzymatic preparations should contain very limited cinnamate decarboxylase, particularly for white wines. This specific enzyme can lead to the formation of ethyl-phenols which can impart unpleasant, 'Brett'-like odors.

The liberation of some grape-derived volatiles can occur as a result of enzymes produced by yeasts. Our research on the effect of yeast strain on glycoside or conjugate hydrolysis showed limited differences among yeast (average 7%) in ability to hydrolyze grape conjugates (abstracts of several research publications are posted at www.fst.vt.edu/zoecklein/index.html). The exceptions were native yeasts. Wines produced by native or uninoculated fermentations showed as much as a 20% greater conjugate hydrolysis.

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.fst.vt.edu/zoecklein/index.html

Phone: (540) 231-5325
Fax: (540) 231-9293
E-mail: bzoeckle@vt.edu