New method helps enhance wine oak barrel aging

The use of wood containers for aging red table wines has been the standard for quality among winemakers around the world for centuries. Wood seals in the wine but still “breathes” enough to allow minute amounts of oxygen to gradually oxidize the wine, giving it a “soft” flavor and pleasing aromas.

And while oak may never be surpassed for the quality wines in produces, advances in technology and monitoring methods are making stainless steel more attractive to tin the industry, reports Fresno State associate enology professor Ken Fugelsang, who also serves as wine-master for the Fresno State Winery and research scientist for the Viticulture and Enology Research Center.

One key advance in the use of stainless steel tanks for aging is a process called micro-oxygenation, Fugelsang notes in a recently published research report.

“Micro-oxygenation is a process whereby young red wines are intermittently exposed to oxygen, supplied in the form of compressed gas via a micron-size diffuser positioned close to the bottom of a stainless steel tank,” he said. “The process is the same as that which would occur during barrel aging, except that the time frame is significantly shortened.”

Despite advances in this technology, industry wine experts continue to question whether the artificial introduction of oxygen may stimulate growth of spoilage organisms which could mar the aging process or the wine itself, Fugelsang said. To help ease these concerns, he has been leading Fresno State efforts to improve methods for monitoring the micro-oxygenation process.

Once phase of this work included developing the analytical methodology to monitor changes in wine undergoing treatment. One such method is to use solid phase micro-extraction to measure a primary analyte, acetaldehyde, formed during the reaction.

“Detection of increases in acetaldehyde can be used by the winemaker or as an analytical tool to monitor the progress of the micro-oxygenation process,” Fugelsang said. The methodology developed in our lab “proved more than adequate to detect and monitor acetaldehyde in wine well before the sensory threshold level of 40-100 milligrams per liter.” In addition, the method is fast, with an average time per analysis of 30 minutes, he noted.

Additional monitoring methods may also be explored using other derivatization reagents such as cysteamine, which is less expensive, he said. In the meantime, these more recent advances will give winemakers a wider choice of analytical tools to support their wine production decisions.

Details of the study are included in a complete final report available through the California Agricultural Technology Institute or on the California State University Agricultural Research Initiative Web site, located at

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