Case Study: Commercialization of Sweet Sorghum Juice Clarification for Large-Scale Syrup Manufacture

The precipitation and burning of insoluble starch granules from sweet sorghum juice on heating coils prevented the large-scale manufacture of syrup at a new industrial plant in Missouri, USA. To remove insoluble starch granules, a series of small and large-scale experiments were conducted at the plant on raw juice extracted by roller milling from two commercial sweet sorghum cultivars Honey Drip and M81E. Both starch concentration and granule size contributed to processing problems. Leaving de-aerated raw juice in settling tanks before clarification settled out a considerable amount of small to medium sized starch granules, but did not remove enough starch. Hot clarification of juice performed better than cold clarification in removing starch and turbid particles. During the USDA hot clarification process (heat to 80 °C; lime to pH 6.5 with milk of lime [360 g/L]; 5 ppm polyanionic flocculant) in the plant, some starch was solubilized. Small to large size starch granules were removed in the clarification mud which improved as settling time progressed. At least 1 h of settling is recommended in the plant. Late in the processing season, scum formed on the surface of the juice that did not contain any starch granules, but did contain microscopic bubbles making the scum less dense than juice and unprecipitable. This highlights sweet sorghum quality differences across the processing season that still need to be addressed along with cultivar differences. Overall, the introduction of juice de-aeration, settling, and clarification steps enabled the large-scale manufacture of syrup and helped to mitigate quality and processing differences due to cultivar and environmental effects and thus assured continual supply to customers.