Background: Achieving optimal fermentation is challenging when the variation within malt starch structure and enzyme activities are not part of the standard malting specifications. This study explores how the variation of starch and starch amylolytic enzymes in both malts and rice adjuncts affect the mashing and the subsequent yeast fermentation in the laboratory-scale production of beer. Results: The addition of rice adjuncts significantly increased the maltose content whilst reducing the glucose content during mashing. The maltotriose content, released during mashing, was significantly negatively correlated with the total amylose content (r = −0.64, p < 0.05), and significantly negatively correlated with the number of amylopectin longer chains (degree of polymerization 37-100) (r = −0.75, p < 0.01). During fermentation, while the content of maltotriose significantly and positively correlated with both the rate and amount of ethanol production (r = 0.70, p < 0.05; r = 0.70, p < 0.05, respectively), the content of soluble nitrogen in the wort was significantly and positively correlated with both the rate and the amount of ethanol production (r = 0.63, p< 0.05; r = 0.62, p < 0.05, respectively). The amount of amylopectin with longer chains was; however, significantly negatively correlated with the ethanol production (r = −0.06, p < 0.05). Small variations among the ethanol concentration and the rate of ethanol production during fermentation were found with the addition of different rice varieties. Conclusions: The effects of the rice adjuncts on the performance of fermentation depends on the properties of the malt, including the protein modification and malt enzyme activities. This study provides data to improve standard malt specifications in order for brewers to acquire more efficient fermentation, and includes useful molecular structural characterisation.Fermentation 2018, 4, 103 2 of 21 diastase enzymes in producing fermentable sugars from malt, as well as malt and solid adjuncts [7][8][9][10][11][12]. However, none of the latter studies investigated the main substrate responsible for the fermentation: starch. One recent study examined the variation of starch structures between malts (and rice adjuncts), and also the starch-degrading enzymes and the resultant fermentable sugars [13]. However, no studies have considered any variations in starch quality, its role in the production of fermentable sugars and its fermentation efficiency. Except for the effects of starch structure, other factors are also involved in altering the release of fermentable sugars. For example, the protein content and the activities of amylolytic enzymes within the barley samples used can affect the release of fermentable sugars during mashing.Starch in barley, like most cereals, is the most abundant component within the grain, but the amount and composition varies depending upon grain type, as well as variety, and the environment the crop was grown in [14][15][16][17]. Starch is a complex branched glucose polymer that is comprised of amy...
