This study investigates the effect of double‐ or single‐stage distillation and different alcohol content in ‘hearts’ (middle fractions) on the distribution of aroma volatiles and undesirable compounds (methanol, hydrocyanic acid, ethyl carbamate) during distillation of plum brandies. Irrespective of the distillation method used, the first fractions (‘heads’) included mainly aliphatic aldehydes, acetals and esters as well as higher alcohols (1‐propanol, 2‐methyl‐1‐propanol, 1‐butanol, 2‐methyl‐1‐butanol and 3‐methyl‐1‐butanol). Furfural, 1‐hexanol, benzyl alcohol, 2‐phenylethanol and ethyl carbamate occurred in relatively high concentrations in the ‘tail’ fractions. Increasing the concentration of alcohol in the heart fractions from 70 to 90% v/v resulted in a gradual decrease in the concentration of all detected volatile compounds. Compared with single‐stage distillation, double distillation produced heart fractions with lower concentration of acetaldehyde and benzaldehyde and with higher contents of furfural and esters, such as isobutyl acetate and isoamyl acetate. There was a statistically significant increase in the amounts of methanol and ethyl carbamate obtained from double distillation compared with similar fractions derived from the single‐stage process. However, in all fractions these compounds occurred in concentrations much lower than the limits specified by EU regulations. The heart fraction from the double‐stage process with 83% v/v alcohol content received the best scores for aroma and flavour. Copyright © 2017 The Institute of Brewing & Distilling

Abstract:The objective of this study was to determine the efficiency of rye and barley starch hydrolysis in mashing processes using cereal malts as a source of amylolytic enzymes and starch, and to establish the volatile profile of the obtained agricultural distillates. In addition, the effects of the pretreatment method of unmalted cereal grains on the physicochemical composition of the prepared mashes, fermentation results, and the composition of the obtained distillates were investigated. The raw materials used were unmalted rye and barley grains, as well as the corresponding malts. All experiments were first performed on a semi-technical scale, and then verified under industrial conditions in a Polish distillery. The fermentable sugars present in sweet mashes mostly consisted of maltose, followed by glucose and maltotriose. Pressure-thermal treatment of unmalted cereals, and especially rye grains, resulted in higher ethanol content in mashes in comparison with samples subjected to pressureless liberation of starch. All agricultural distillates originating from mashes containing rye and barley grains and the corresponding malts were characterized by low concentrations of undesirable compounds, such as acetaldehyde and methanol. The distillates obtained under industrial conditions contained lower concentrations of higher alcohols (apart from 1-propanol) than those obtained on a semi-technical scale.

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The rising population and increasing demand for food place added pressure on the agricultural sector to maintain high process efficiency while implementing environmentally friendly methods. In this study, we investigate the effect of pre-hydrolysis of native rye starch and its influence on the yield of ethanol obtained by simultaneous saccharification and fermentation (SSF) from high gravity rye mashes with 25% and 28% w w −1 dry matter content. Fermentation was carried out in a 3-day system at a temperature of 35 ± 1°C using the dry distillery yeast Ethanol Red (Saccharomyces cerevisiae). The characteristics of the tested raw material and changes in the native rye starch during enzymatic hydrolysis were analyzed using a scanning electron microscope (SEM). The SEM images revealed characteristic changes on the surface of the starch, which was found to have a layered structure, as well as interesting behavior by the yeast during SSF when the glucose concentration in the environment was lowered. Both in the mashes with 25% and 28% w w −1 dry matter, starch pre-hydrolysis did not significantly increase either the initial amounts of sugars available to the yeast or the fermentation efficiency and ethanol yield in comparison to the mashes without this pre-treatment. Keywords Native starch. Pre-hydrolysis. Fermentation. SSF Abbreviations A 100 absolute alcohol AP amylopectin BD amylopectin of the high-amylopectin cultivar CU Ceralpha unit cv cultivar d.m dry matter DP degree of polymerization DSS degree of starch saccharification GSHE granular starch hydrolyzing enzymes HPLC high-performance liquid chromatography LSD least significant differences PES polyethersulfone PLS pressureless liberation of starch SEM scanning electron microscope SSF simultaneous saccharification and fermentation SSU soluble starch unit VHG very high gravity GAU one glucoamylase unit