Enology Notes

Enology Notes #36 January 7, 2002

To: Virginia Vintners

From: Bruce Zoecklein

Subject: Winemaker Roundtable Meetings: Cork Quality Control and Microoxygenation Research, Cork Quality

I will host two Winemaker Roundtable meetings in January:

The subjects will be cork quality and an update on our microoxgenation research. Bruce Scott of Scott Labs will join me for a discussion of the issues related to cork quality. Bruce will review the current body of knowledge with regard to cork taint, discuss the impact on the industry, and what people should be thinking about with regard to corks and cork quality.

I will present and discuss some of our research findings with regard to microoxgenation of red wines.

If you are a commercial Virginia producer, please join us for one of these meetings. Both programs are the same. Note, one begins in the afternoon, the other in the morning. If you plan on attending the morning meeting, bring a bag lunch.

Corks and Wine Quality. Over 50 naturally occuring volatile compounds have been identified in defect-free cork. These include phenolic aldehydes, such as vanillin, phenols, and fatty acid esters, and furans, such as furfural. Cork taint, however, results from the contributions of a relatively small group of volatile metabolites linked by their musty odor and flavor-active properties. These include chloroanisoles, 1-octen-3-one and 1-octen-3-ol, 2-methylisoborneol, and guaiacol.

In the U.S., the incidence of cork taint is reported to range from 0.5% to more than 2%. Whether or not cork exhibits taint upon bottling may depend on its intrinsic structural integrity. Imperfections, such as cracks, increase available surface area for extraction and, therefore, the potential for development of off odors.

How does cork grade impact the incidence of cork taint? One study suggested that more expensive corks show greater incidences of taint, suggesting that these may be stored for special use and, hence, potentially subject to storage-related mold growth.

The primary compound implicated in cork taint is 2,4,6-trichloroanisole (TCA). Its extraordinarily low sensory threshold in wine (reported to be 1.4 ng/L) makes TCA particularly problematic. Other chlorophenols which have very low sensory thresholds may be involved. Additionally, a variety of other compounds have been reported to elicit musty odors in wine. These include guaiacol, geosmin, and 2-methylisoborneol. What all of this means to the winemaker will be discussed at the Roundtable Meeting.

Microoxygenation Research. As reported in previous editions of Enology Notes and the Vintner's Corner (posted on-line at www.fst.vt.edu/zoecklein/index.html), microoxygenation is a process whereby young wines are continuously exposed to oxygen. Oxygen, supplied via a micron-size gas diffuser, catalyzes the oxidation of ethanol to acetaldehyde which acts as bridging agent linking anthocyanins and other phenols. At the Roundtable Meeting I will discuss the results of our research on this process and have wines for evaluation.

Happy Holidays!

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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