Impact of Storage Time on the Juice and Sugars Extracted from Chopped and Whole Stalk Sweet Pearl Millet and Sweet Sorghum Biomass

Since they have a high concentrations of fermentable sugars, sweet pearl millet and sweet sorghum are two interesting crops for bioethanol production. However, if the juice is not extracted from the biomass immediately after harvest, the biomass has to be transported and stored for further juice extraction. This delay could affect the amount of juice extracted and its sugar concentration. This paper presents the results of 3 years of experiments where different storage modes (chopped and whole stalks) and various storage time (0 to 14 days) were applied on two different crop species (sweet pearl millet and sweet sorghum). Storing sweet pearl millet as whole stalks for 2 weeks resulted in a water-soluble carbohydrate (WSC) concentration decrease of 52 %, while no significant decrease of the WSC concentration was observed for sweet sorghum. Whole stalks storage is much more efficient than storing the biomass chopped to avoid a rapid sugar loss. However, more juice can be extracted from stored chopped biomass than from stored whole stalks biomass. If the juice cannot be extracted quickly after the harvest, the biomass can be stored as whole stalks to avoid rapid sugar deterioration, especially for sweet sorghum.