Lynne Wong's PhD thesis

Qin and White (1991) dried well-washed and sieved bagasse at 60 °C in an atmospheric
oven for 8 hours and stored it in a desiccator. A weighed amount (8 g) of dry washed fibre
was transferred to the cylinder of the hydraulic press (see Fig 4.1) and a weighed mass (24
g to 48 g) of sucrose solution of known Brix was added. The fibre was then compressed
by the press causing liquid to appear through the open cylinder. When the hydraulic
pressure was released, the fibre stayed as a compressed plug and needed to be released by
digging with a small fork. The pressing and forking procedure was then repeated for the
required number of pressings. A sample of the final juice was taken with a syringe, filtered
and analysed in a refractometer. The same equation as that of Mangion and Player above
applies.
Qin and White (1991) found significant differences in Brix-free water values for rind fibre,
stalk fibre and stalk pith fractions in the test bagasse; they were 11.9, 18.3 and 22.1%
respectively when a 5° Brix sucrose solution was used as the contact solution.
4.3 VARIABLES THAT AFFECT BRIX-FREE WATER DETERMINATIONS
Factors which affect the Brix-free water values are numerous and have been investigated
by various research workers. They are enumerated in the following section.
4.3.1 Concentration of contacting solution
Qin and White (1991) found that the Brix-free water of cane fibre decreased as the
concentration of the contacting sucrose solution increased. Also the analytical errors
decreased because the concentration change became larger. This trend agreed with the
observations of Van der Pol et al. (1957) and Kelly and Rutherford (1957), although the
absolute values found by Qin and White for sieved bagasse were lower than their values
for cane fibres (with higher temperature fibre drying). The values obtained by Kelly and
Rutherford varied with the cane variety, with Brix-free water values up to 130% for one
cane variety.
4.3.2 Drying temperature of fibre
The morphological history of the fibre is reported to have considerable effect on the Brixfree
water value. Van der Pol et al. (1957) found a difference of five units in the Brix-free
water values for cane dried at 60 °C (over phosphorus pentoxide and under vacuum)
compared to the higher value obtained for the same fibre at 125 °C. Drying at 60 °C may
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