Effects of germination duration on enzymatic activities, starch structure, and brewing quality of black barley malt

Abstract

Owing to its antioxidant capacity and pigmentation, Black barley (Hordeum vulgare L.) is a promising cereal for specialty malts and dark beer production. However, its low enzymatic activity during malting can reduce processing efficiency. In this study, we aimed to evaluate the malting performance of a domestic black barley cultivar using five germination treatments (M95–M115), corresponding to germination durations of 95–115 h. As coleoptile elongation increased with germination time, α- and β-amylase activities rose significantly, while malt yield, crude protein, and crude fat content declined. Scanning electron microscopy and amylopectin chain length distribution analyses revealed progressive starch degradation and a shift toward shorter chains. Treatment M105 achieved the best balance of fermentable sugars (maltose and oligosaccharides), high free amino nitrogen, and low bitterness. M115 yielded more ethanol due to higher enzymatic activity; however, its sugar profile was less favorable for brewing. Overall, coleoptile elongation correlated more strongly with malt and beer quality traits than germination time alone. These findings suggest that coleoptile elongation is a more reliable indicator for optimizing malting conditions in pigmented barley and support cultivar-specific approaches for specialty brewing.