Yeast and Fermentation Session
Seung K Park, Kyung Hee University, Yongin-Si, Gyeonggi-Do, Korea
Co-author(s): Beom Seon Lee and Joo Seok Bang, Kyung Hee University, Yongin-Si, Korea
ABSTRACT: To study the potential impact of hydrogen sulfide (H2S) production from residual sulfur on leaf hops, increasing levels of elemental sulfur were spiked into the wort and fermented by lager yeast. One representative dried leaf Perle hop selected from our previous studies was washed with tap water in order to remove any residual sulfur that might be left on the leaf hop at harvest. Six increasing levels of elemental sulfur (0, 1, 2, 3, 4, and 5 mg/L) were spiked into wort that had been hopped with washed hops previously. Fermentations were conducted at 15°C in laboratory scale fermentors. Non-washed hops were used as a control to compare the H2S production with the sulfur-spiked wort samples. H2S production was quantitatively measured at 24-hr intervals using a H2S detection tube method developed in our lab. Residual H2S levels in the finished beers were also determined using the H2S detection tube method. Yeast produced the highest levels of H2S during the active fermentation period, and a high level (>3 ppm) of sulfur spiking produced higher levels of H2S during fermentation, and the H2S concentration (>5 ppb) remained high in the resulting beers. Increasing addition of elemental sulfur to certain levels, however, did not proportionally produce increased levels of H2S, indicating that specific yeast-sulfur interactions during fermentation were apparent.
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.