Journal
BIOCHEMICAL ENGINEERING JOURNAL
Volume 77, Issue -, Pages 1-6Publisher
ELSEVIER
DOI: 10.1016/j.bej.2013.04.016
Keywords
Fermentation; Yeast; Protease; Ethanol; Free amino nitrogen; Beer foam
Funding
- National Science-Technology Supporting Project for 12th Five-Year Plan [2013AA102108-6]
- Key Technology R&D Program of Guangdong Province [2012A080107005, 2011A020102001]
- Fundamental Research Funds for the Central Universities [2012ZM0069]
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Nitrogen limitation, particularly prevailing in the case of high gravity beer brewing, results in poor yeast viability and even stuck or sluggish fermentations. Although wort contains abundant proteins and longer chain peptides, brewer's yeast does not assimilate them due to the fact that cells hardly secrete proteases during fermentation. The objective of this study was to investigate the possibility for utilizing unavailable nitrogen from two types of high gravity worts (20 degrees P and 24 degrees P) by adding three food-grade commercial proteases (Neutrase, Flavorzyme and Protamex) at the beginning of fermentations, respectively. Results showed that proteases supplementation significantly increased the FAN level and thus the amount of cell suspension in the later stages of fermentations (ca. 10 days later for 20 degrees P and 25 days later for 24 degrees P) (p < 0.05). Among the studied three proteases, we found that fermentations with Flavorzyme supplementation exhibited the best fermentation performance in terms of significantly improved wort fermentability, higher ethanol yield and flavor volatiles formation (p < 0.05). Furthermore, the foam of final beers produced by adding proteases was as stable as that of the control at each of the corresponding gravities. (C) 20113 Elsevier B.V. All rights reserved.
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