Extraction of the Sugary Juice from Sweet Pearl Millet and Sweet Sorghum Using a Hydraulic Press and a Four-Roller Press

Abstract

<abstract> <b><sc>Abstract.</sc></b> Sweet sorghum and sweet pearl millet have good agro-industrial potential because they can be used as energy crops, using the sugary juice contained in their stalks to produce bioethanol, while the bagasse (pressing residues) can be used as animal feed. However, the process of extracting the juice and consequently the sugar from the biomass of these crops needs to be explored. For this study, two experimental presses, a four-roller press and a hydraulic press, were designed and built at the Department of Soils and Agri-Food Engineering of Université Laval, in Quebec, Canada. With bioethanol production in mind, an experiment was carried out using the hydraulic press to investigate the effects of stalk chopping mode (fine vs. coarse) and various compressive forces, as well as a comparison between the two presses, to determine the more suitable press for extracting the sugary juice from these crops with or without leaves. The roller press gave good results with sweet sorghum, as no significant difference between the presses was found in the volume of juice extracted if the leaves were removed prior to extraction. However, the hydraulic press was more suitable than the roller press for extracting juice from sweet pearl millet. Chopping mode did not have any effect on the volume of juice extracted. Leaves should be removed prior to pressing with the roller press. When using the hydraulic press, leaf removal was necessary only with sweet sorghum. An estimated ethanol yield of 1956 L ha^-1 could be achieved using the hydraulic press to extract the juice from sweet sorghum without leaves.