Hygroscopic water in sugarcane : final report 114

Abstract

At the 1989 Workshop on Cane Analysis conducted by the Sugar Research Council it emerged that the best technical method of cane analysis for the Australian industry was the direct cane analysis method (DCA) employing the wet disintegrator technique. This method involves comminuting a sample of prepared cane with a weighed amount of water and then analysing the resultant liquid extract. The analysis of cane is determined by calculation, making allowance for the degree of dilution by the added water. This calculation also makes allowance for some water in sugar cane which is not available for solution of the dissolved substances in juice. This water is commonly referred to as bound water or hygroscopic water.

The usual calculations with DCA involve the use of a value for hygroscopic water of 25 percent of the fibre percentage. The origin of this 25 percent figure cannot be determined but it is believed that it came about at the time of the method's development when it represented an approximate average of the data available at the time. Because early data showed a wide range of values reflecting possibly variations from one type of cane to the next and analytical errors, it was decided to attempt the rigorous determination of hygroscopic water in sugar cane with the benefit of today's better analytical instruments.

The author has found the same difficulties that were experienced by the earlier Horkers but an attempt has been made to show how much the variability in results can be attributed to the many causes. We think that the traditional 25 percent of fibre figure may be a little high for today's canes especially considering that the fibre as determined by traditional methods includes 1-2 percentage units of dirt. The hygroscopic water associated with dirt is much lower than that for true cane fibre. A more realistic value would probably lie between 15 and 20 percent of fibre.