OBSERVATIONS OF THE HARVESTING, TRANSPORTING AND TRIAL CRUSHING OF SWEET SORGHUM IN A SUGAR MILL

SWEET sorghum has previously been evaluated as having the potential to contribute fermentable sugars to a bioenergy industry producing ethanol. Sweet sorghum grown and processed complementarily with sugarcane can potentially increase efficiency of production by utilising existing infrastructure to harvest, transport and extract fermentable sweet sorghum sugars. This paper reports observations of a trial of sweet sorghum harvest, transport and crushing at Mossman Central Mill at the conclusion of the 2002 sugarcane crushing season. A 15 hectare sweet sorghum plant crop was harvested with a cane harvester in two separate batches: 1. with the harvester?s extractor fans operating; and 2. with the harvester?s extractor fans turned off. Each batch was transported and crushed with existing sugarcane infrastructure. The first ratoon of sweet sorghum was harvested with a forage harvester. The bulk density of forage harvested sweet sorghum is approximately 400 kg/m3 compared with approximately 300 kg/m3 for sugarcane and 200 kg/m3 for sweet sorghum harvested with a cane harvester. The higher bulk density material is cheaper to transport, placing limits on the geographical area in which cane harvested sweet sorghum could be sourced. A deterioration analysis showed a slight reduction in juice extraction percentage and no reduction in brix of extracted juice of cane harvested sweet sorghum. Brix declined rapidly in forage harvested sweet sorghum over the first 42 hours after harvest. Juice extraction percentage exhibited a similar trend to cane-harvested sweet sorghum. There are significant cut-to-crush limitations of forage harvested sweet sorghum due to the rapid decline in brix of extracted juice. Comparisons of both batches of sweet sorghum were made with sugarcane crushed at the same mill settings for moisture, brix and fibre of fibrated material prior to entering No. 1 mill and after the final mill. Brix extraction percentage was lower for both batches of sweet sorghum than sugarcane. Fibre levels of sweet sorghum are higher and final moisture for sweet sorghum is comparable with sugarcane.