Waste Bread as a Raw Material for Ethanol Production – Effect of Mash Preparation Methods on Fermentation Efficiency

The issue of managing waste bread is a global concern, with significant environmental and the economic implications. The utilisation of waste bread for bioethanol production, employing energy-saving tech-nology, could prevent these consequences and reduce the consumption of traditionally used fossil fuels. The objective of this study was to evaluate the influence of the type of waste bread (wheat and wheat-rye sourdough) and the mash preparation method on the results of alcoholic fermentation and the concen-tration of selected congeners in the distillates. The highest fermentation efficiency (96% of theoretical) was achieved for both types of bread through the utilisation of the pressureless starch liberation method combined with simultaneous saccharification and fermentation. The separate saccharification of starch did not result in an enhanced efficiency of the process. Despite a slight reduction in efficiency of the process, the hydrolysis of native starch was regarded as a promising solution for the processing of waste bread to ethanol. All of the obtained distillates exhibited a low concentration of methanol. The elevated acidity and aldehydes levels, in relation to the national recommendations, indicate the potential necessity for the separation of the volatile congeners depending on the intended use of the obtained spirit distillates.