Recovery of Sugar From Dried Stems of Sweet Sorghum [Sorghum Bicolor (L.) Moench].

Sweet sorghum [Sorghum bicolor (L.) Moench] is a useful source of both sugar and cellulose for ethanol production.  However, most efforts on the production and utilization of sugar have relied on techniques developed for sugarcane (Saccharum spp.).  The objective of this research was to determine the quantity of sugar that would be recoverable from dried stems of various sorghum types.  The sweet sorghum cultivar ‘Topper’ and a high biomass, low sugar containing hybrid ‘70327’ were grown in replicated plots at Hays KS.  At harvest, individual plants within each plot were harvested and stem diameter was determined.  Plants were placed into 3 groups based upon stem diameters of less than 1.9cm, between 1.9 and 2.5 cm, and greater than 2.5 cm.  Each group was then subdivided into 2 samples.  One sample was immediately chopped with a silage cutter, a wet sample was taken and weighed and then the juice was pressed out, quantity of juice measured, and a Brix reading was taken.  The remaining wet cake was weighed and then dried and weighed for dry matter determination.  The other sample was allowed to dry naturally in the field and then stored for 6 months.  To extract sugar from the dried sample, 200 ml of water (100C) was added to 20 g of ground stover, mixed for 5 minutes, the supernatant filtered, measured, and a Brix reading taken.  Results showed that for the sweet sorghum, larger stems produced more sugar per gram dry matter.  For the non-sweet hybrid, stem size did not affect sugar production on a dry matter basis.  Sugar recovered from dried stems 6 months after harvest averaged 80% as much, on a dry matter basis, as that recovered from freshly harvested stems for both genotypes at all stem sizes.