Design and Testing of a Four-Roller Press to Extract Sugary Juice from Sweet Sorghum and Sweet Pearl Millet Biomass

Abstract

<abstract> Sweet pearl millet and sweet sorghum have great potential for bioethanol production, because the sugary juice contained in their stalks can be extracted and eventually fermented to produce ethanol while the pressing residues can be used as livestock feed. However, the juice extraction process needs to be optimized. With a view to an in-field extraction process, a four-roller press was designed and built at the Department of Soils and Agri-Food Engineering of Université Laval, in Quebec, Canada. Three different roller speeds and one or two pressing runs were tested for extracting the juice from sweet pearl millet and sweet sorghum biomass. The results showed that the roller press might not be suitable for extracting the juice from sweet pearl millet, given the average moisture extraction of only 6.2% for that crop, in comparison with 24.6% for sweet sorghum. However, a slower roller speed, as well as multiple pressing runs, increased juice extraction by 51%. These two independent variables did not have any significant impact on the juice sugar concentration. With this specific roller press, it is therefore recommended to press the sweet sorghum biomass more than once at the slowest speed to extract the maximum amount of juice and therefore of sugar.