Characterization of Unmalted Barley Treated with Aspergillus oryzae

Abstract

Koji is a complex of substrate and the filamentous fungus Aspergillus oryzae. It is used for saccharification in fermented foods and beverages. Its role in co-fermentations is known, but its application in beer brewing contexts is unclear. The goal of this study was to determine what effect A. oryzae has on the characteristics of unmalted barley in brewing contexts, if it might bypass traditional malting, and what sensory attributes a koji beer might exhibit. Koji barley was prepared with pearled barley and a red rice koji strain and compared to untreated pearled barley and malted barley control groups. The total production time of koji barley was nine days and the process consumed 4 ± 2 L water per kg of grain. Coarse grind extract in koji barley was three times greater than pearled barley while approximately ten percent less than malted barley. Diastatic power was over three times greater in malted barley versus koji barley, while no significant difference (p < 0.05) was found between koji barley and untreated pearled barley. Koji barley congress wort exhibited three times more glucose but less than half the maltose content of malted barley wort. Analysis of wort organic acids showed increased concentrations of citric, succinic, and kojic acid in koji barley versus pearled barley. Qualitative sensory analysis of fermented koji barley wort identified moderate tropical, citrus, and sour flavors as well as green apple and tropical fruit aromas. The results demonstrated that koji barley shows characteristics similar to specialty malts and may favor hazy, fruited, and sour beer styles.

Keywords:

• Aspergillus oryzae
• barley
• brewing
• koji
• malting
• sour beer

Acknowledgements

The authors would like to thank Dr. Folarin Oguntoyinbo for taking the time to participate in sensory panels. A special thank you is extended to Ivory Tower, the A.R. Smith Department of Chemistry and Fermentation Sciences, and the Appalachian State Office of Student Research for providing funding for this research.