Malting and Brewing Performance of β-Amylase-Deficient Barley

beta-Amylase (alpha-1,4-glucan maltohydrolase; EC 3.2.1.2) is known to be an important enzyme in beer brewing. To identify the contribution of beta-amylase in more detail, two beta-amylase-deficient barley, 'Backcrossed line (BCL)-Haruna' and 'Nittakei 81', were used for the investigation of malt quality and brewing characteristics. 'BCL-Haruna' was bred by the backcross method for the introduction of the beta-amylase-deficient trait from landrace barley ('Tibet Violet 1') to Japanese traditional malting barley 'Haruna Nijo'. 'Nittakei 81' was bred by crossing between Japanese malting barley 'Sukai Golden' and 'Tibet Violet 1'. With regards to the malting quality under 41.0% target cast moisture in micro-malting, the diastatic power (DP) and apparent attenuation limit (AAL) of 'BCL-Haruna' and 'Nittakei 81' were 408 oWK and 416 oWK and 12.4% and 14.8% lower than those of the control variety 'Haruna Nijo'. Oligosaccharide analysis indicated that the maltose concentration of the 'Nittakei 81' wort was 19.7 g/L lower in comparison to a standard European malting barley 'Propino' wort, although the maltotetraose and maltopentaose concentrations of the 'Nittakei 81' wort were 5.6 g/L and 2.7 g/L higher than those of the 'Propino' wort. After fermentation, the alcohol concentration of the 'Nittakei 81' beer was 0.67% lower compared with the 'Propino' beer, and the extract and concentrations of maltotetraose and maltopentaose of the 'Nittakei 81' beer were 5.0 g/L and 2.5 g/L higher than those of the 'Propino' beer. The results indicate that the beta-amylase-deficient barley has a unique malting quality, especially lower DP and AAL, which might induce inadequate starch degradation or fermentation. However, this trait caused no serious issues during the brewing process, suggesting the possibility of beta-amylase-deficient barley as a unique brewing material including low-alcoholic and non-alcoholic beer production with a specific saccharide composition.