Post Harvest Deterioration of Burnt Cane in Bundles

Recently attention has been focused on cane quality as a means of improving the overall performance of the South African sugar industry. Work by the SMRI pioneered the use of ethanol as an indicator and showed a loss of between 2 and 3% of the mass of sucrose in fresh cane for every 1 000 ppm ethanol on brix. Results obtained during the implementation of this procedure routinely during the 1991 season at Tongaat-Hulett mills were queried on the basis of high ethanol levels coupled with high purities. To answer these queries and gain more information on the losses associated with deterioration two trials were run at Mount Edgecombe mill during August/September and November/ December. Mass losses from large bundles were lower than previously measured on smaller bundles at 0,4% to 0,8% per day. The mass of sucrose lost was also much lower at approximately 1,0% for every 1 000 ppm ethanol formed. The e f fect on overall sucrose recovery was estimated to be a drop of between 0,1 and 0,2 units per 1 000 ppm ethanol. Introduction One of the major concerns in the industry has been the deterioration in the quality of the cane delivered to the mill due to excessive delays between cutting and crushing. Lionnet (1986) examined the results of deterioration and together with Pillay, (1987, 1988) developed the procedure of monitoring of ethanol levels in DAC extract as a means of estimating delays. In the most recent paper by de Robillard et al., (1990), the sucrose lost due to deterioration was determined to be between 2 and 3% of the mass of sucrose in fresh cane for every 1 000 ppm of ethanol on brix. The average level of ethanol in cane at Illovo, where the work was done, was found to be approximately 4 000 ppm on brix. Based on these findings a programme of monitoring ethanol levels in DAC extracts has been instituted at all the TongaatHulett mills, with the mass of pol lost being estimated according to de Robillard's results. While the programme has worked well in providing evidence of delays, doubt has been expressed about the accuracy of the pol loss factor. This has been brought about by high ethanol levels coupled with high purities on some deliveries which would indicate very high fresh cane purities. To answer these queries and to gain more information on the process and consequences of cane deterioration, two tests were carried out at Mount Edgecombe, one during the middle and one at the end of the season. These tests were planned to increase the data on which the estimates of deterioration loss are based. New aspects which were brought into the tests were the measurement of mass loss on full sized cane bundles and the estimation of the effects of deterioration on overall recovery in the mill. Method Both tests followed the same basic pattern. A field on Blackburn Estate was chosen, burnt and harvested as quickly By M. G. S COX and P. SAHADEO Tongaat-Hulett Sugar Ltd, La Lucia 220 as possible. The first two bundles were sent to the mill for crushing with the minimum delay and the rest of the cut cane was stored in chained bundles in the loading zone. Twenty-eight bundles of eight tons each were stored for the first trial and slightly less for the second. The bundles were then delivered to the mill, two at a time, at predetermined intervals over 21 days. The bundles were crushed consecutively to allow the SICB sample to be taken with confidence. In the first trial, the mass loss was determined on a triangular stack of ten 50 kg bundles which were weighed daily and restacked in the same positions. For the second trial a four ton bundle was stored on a trailer in the mill yard and weighed on the weighbridge at the same times as the test deliveries. The normal SICB sampling procedure was used and from this the DAC analysis was obtained plus a sample of DAC extract for ethanol analysis. Expressed juice samples were also obtained by pressing prepared cane samples in a hydraulic press. These were used for the gas chromatographic (GC) sugar and ash analyses needed in the recovery calculations. The pol of the expressed juice was measured to allow pol/sucrose ratios to be calculated and a comparative ethanol analysis was also done. Results and discussion The analyses from both tests are detailed in the Appendix (Tables 1 to 4). Mass loss The mass loss determination on the first trial showed a significant dif ference between mass loss of the bundles on the outside of the stack and those on the inside or on the ground. Figure 1 compares the average mass loss rates of the five outside bundles with those of the five inside bundles.