An Integrated Approach to Harvest and Storage of Sweet Sorghum at Farm Scale

A major constrain for sweet sorghum (Sorghum bicolor L. Moench) establishment as a reliable biofuel feedstock is the fast biomass degradation immediately after harvest due the high content of soluble sugars and their rapid fermentation that considerably decrease the actual ethanol yield. Such a drawback does not allow storing of sorghum for a reasonable period forcing the industry to process it immediately with consequent problems of handling, logistic, and plant size. Therefore, an appropriate harvesting and storage technique to prevent sweet sorghum juice degradation is urgently needed to ensure economic benefits to farmers. An efficient and cost-effective way to overcome this obstacle could be an on-farm storing system of undistilled ethanol from sweet sorghum juice, while the remaining bagasse could be ensiled and exploited for complementary energy generation. The objective of this study was to evaluate different harvest methods and storage techniques aiming to a low cost and efficient on-farm processing systems to store sweet sorghum biomass. Harvesting in the hard dough stage and defoliating the plants before juice extraction resulted in higher ethanol yield. The use of commercially available fructophilic yeasts allows maximizing undistilled ethanol yield and on-farm storing for about 1 year without spoilage. The residual bagasse was ensiled and inoculated with Lactobacillus bacteria commonly used in forage conservation which significantly improved its quality as feedstock for biogas fermenters. In conclusion, the integration of low-cost harvesting and storage techniques with the valorization of sweet sorghum by-products are worthwhile management strategies to be further developed.