Effects of variety, agronomy, malting and mashing conditions on diastatic power of barley

Abstract

A method to measure diastatic power (DP), a - and ß -amylase rapidly from the same barley malt sample has been developed. A separate method to assay the levels of 'free' and 'total' limit dextrinase (LD) in malt has also been implemented. These methods were modified to measure the 'total' DP in barley, by incorporating 100mM cysteine in the extraction buffer. This was used to predict the DP produced by the final malt.

A wide range of barley varieties, grown at several sites in England, Wales and Northern Ireland were malted on the 350g scale. The resultant malts were analysed for DP, a - and ß -amylase and 'free' and 'total' LD. The results show that DP is highly correlated with ß -amylase. DP and b -amylase are more dependent on the variety of barley, whereas a -amylase and LD are more dependent on where the barley is grown.

The steep regime, aeration, germination time and temperature, use of gibberellic acid and kilning schedules were varied to optimise DP production. Of these parameters, kilning regime had the greatest effect on DP, with standard ale kilning reducing both b -amylase and LD dramatically. The other parameters can be used to increase the DP potential of barley, with aeration, low germination temperature for an extended period, addition of gibberellic acid and high cast moistures being optimal.

The effect of DP on various mashing regimes was investigated. Malt with a DP greater than 100° IOB could convert up to 80% adjunct readily. Mashing regimes could be used to influence the carbohydrate spectrum of the wort. Mashing with a proportion of high 'free' LD malt, such as 9-day germinated barley, generated an increased proportion of fermentable sugars at the expense of branched dextrins. This wort was brewed to produce a low carbohydrate beer with no detrimental flavour effects from 'green' notes.