A California State University, Fresno enology research team has made advances in fermentation techniques by identifying methods of detection and control of yeasts that grow naturally on red wine grapes.

Microbiologist Roy Thornton, a professor and scientists for the Viticulture and Enology Research Center (VERC) at Fresno State, recently completed a study of two new methods for detecting the indigenous yeasts. The methods are known as flow cytometry (FCM), and Fourier Transform Infra Red (FTIR) spectroscopy.

The research was prompted by current trends in winemaking featuring the use of indigenous yeasts. These yeasts – found on the skin of the grapes as they are harvested, can produce pleasing new flavors and aromas in wine when compared to the use of conventional yeasts, but the “spontaneous” yeast fermentations also can produce an assortment of undesirable characteristics if they are not properly controlled.

With the help of fellow VERC research scientist Susan Rodriguez, Thornton successfully developed antibodies that could be used in a process to identify two of the indigenous yeasts, Hanseniaspora/Klorckera and Metschnikowia pulcherrima. With that accomplished, he was able to use two experimental tracking procedures to determine how the two yeasts performed under different fermentation regimens.

As part of his conclusions, Thornton determined that the two indigenous yeasts “can compete with other yeasts in wine grape fermentations and survive in sufficient numbers to present possible spoilage threats to the wine.”

He also found that one of the yeasts, Hanseniaspora/Klorckera, showed resistance to sulfur dioxide, which is typically used to eliminate bacteria and sensitive wine grape yeasts.

For more information on this work, contact Thornton at rthornton@csufresno.edu.

(Copy by Steve Olson of the California Agricultural Technology Institute at Fresno State.)