Monitoring ester formation in grape juice fermentations using solid phase microextraction coupled with gas chromatography-mass spectrometry.

Volatile esters contribute important floral and fruity sensory properties to wine. Numerous factors influence the biosynthesis and hydrolysis of esters throughout yeast fermentation; however, methods to monitor the dynamic changes in ester production that occur during winemaking processes are limited. In this study, we showed that solid phase microextraction (SPME), a rapid, solventless sampling procedure, combined with GC/MS analysis is a useful method for the nearly continuous analysis of volatile compounds such as esters that are produced during fermentation. Accuracy, precision, and limits of quantification were comparable to those of other sample preparation methods such as liquid-liquid extraction. Using GC/MS-SPME to monitor fatty acid ethyl esters and acetate esters, we obtained detailed information on the production patterns of ester formation during fermentation. This method now enables the monitoring of volatiles during fermentation and can provide greater insight into yeast metabolism and flavor formation.