Effects of stem length and storage duration on sugar losses in Sweet sorghum

Sweet sorghum (Sorghum bicolor (L.) Moench) is a multi-purpose crop, yielding fuel in the form of ethanol from its stem juice, food in the form of grain, and fodder from its leaves and bagasse. The sugars utilized for bioethanol production are contained in the stalks, in an amount varying between 12% and 25% of the fresh biomass, according to the genotypes and harvesting time. However, these carbohydrates can be easily lost during harvest and post-harvest, because of wrong machinery settings and prolonged periods of exposure of the cut material to the action of fermentative agents. For these reasons, the production of biofuel from sweet sorghum is very sensitive to harvest systems and storage methods, as they can influence remarkably the final energetic yield of the crop. The main objective of the present study was to monitor the time course of dry matter and sugar content in sweet sorghum stem over a long-time storage period. The analysis was carried out by dividing the stems into portions of different length in order to test different storage configuration by varying the stem portion stored to simulate the action of different harvest machines. This work has been designed to take into account a larger storage window respect previous experimentation. The research has provided evidence that sugar loss during the storage is highly influenced by the length of the stem portion, as well as by storage conditions. Total sugar content at harvest was on average 23.2%. The decreasing of sugar content continued during the storage period but at different rate for the different portions. At the end of storage, the sugar content of the whole stem was on average 6.6%, while the smallest portion (1/16 of the whole stem) had an average content of 1.0%. Indications on best storage conditions (storage form, storage location, storage ambient condition), as well as technical details regarding new potential harvesting solutions to decrease the speed rate of sugar loss have been provided.