Bioethanol fermentation of clarified sweet sorghum (Sorghum bicolor (L.) Moench) syrups sealed and stored under vegetable oil

Sweet sorghum represents a readily available renewable carbohydrate feedstock for biofuel production. Generally, the sweet sorghum growing season and window for processing is short and it is often desirable to store a sugar-rich material for future processing. Therefore, we investigated the possibility of storing three different sweet sorghum sugar syrups under a layer of soybean oil; then we investigated subsequent yeast bioethanol fermentation. A layer of oil on the surface of the syrup reduced sugar loss in 30 and 40 degrees Bx syrups, but the loss was still 21-36 %. Storage of 50 degrees Bx syrup resulted in an 11-18 % loss of sugars with or without a surface layer of oil. Elevated levels of lactic and acetic acids, caused by bacterial contamination, almost completely inhibited yeast fermentation; however, when ethanol-producing microorganisms were part of the contamination, stored syrups produced a bioethanol at a yield of 83-91 %, compared to theoretical.