Yeast and Fermentation Session
Seung K Park, Kyung Hee University, Yongin-Si, Gyeongi-Do, Korea
Co-author(s): Beom Seon Lee and Joo Seok Bang, Kyung Hee University, Yongin-Si, Korea
ABSTRACT: Hop is an essential ingredient in brewing; however, there is a lack of understanding as to how hop addition affects hydrogen sulfide (H2S) production during fermentation. In this study, five dried leaf hop varieties were investigated for their H2S production during fermentation by lager and ale yeasts. Laboratory scale fermentations were conducted in a 2 L bottle with a commercial malt extract. Fermentation temperatures were 10 and 15°C for lager and ale, respectively. Quantitative measurements of H2S were carried out at 24-hr intervals using an H2S detection tube method (FIGASA sulfur stick) that was easy, convenient, and reliable for quantifying H2S production throughout fermentation. A lengthy lag period was observed for lager fermentation at lower fermentation temperature, whereas ale yeast fermented at 15°C started fermentation immediately after yeast pitching. Lager yeast produced much higher levels of H2S, while ale yeast produced only trace levels or none. Two or three distinctive H2S peaks were observed from lager fermentation during the course of fermentation, and the highest levels of H2S were produced when the yeasts were actively fermenting the wort. Different hop varieties exhibited various levels of H2S production, with the levels between 33 and 46 µg/L for lager yeast; ale yeast produced trace levels or none regardless of hop varieties. This result indicates that hops and yeast strains are the potential sources of H2S overproduction. Accordingly, identifying sources of H2S production such as yeasts and hops in brewing can significantly reduce H2S levels.
Seung Park obtained a B.S. degree in food science and technology in 1981 from Kyung Hee University in Korea and then joined the Technical Research Institute of Dong Suh Foods Corporation (a joint venture of Kraft Foods in the United States), where he has worked on coffee flavor chemistry, technology, and process engineering for instant coffee manufacturing. From 1986 tot 1993, Seung attended the University of California at Davis, where he received M.S. and Ph.D. degrees in food chemistry and biochemistry, specializing in wine flavor chemistry. He was a post-doctoral researcher at Ernest and Julio Gallo winery research laboratories in Modesto, CA. Currently, Seung is a professor of food chemistry and analysis at Kyung Hee University in Korea, and his major research interests include wine and beer flavor chemistry and biochemistry, especially development of new analytical methods that are important for the quality improvement of wine and beer products.