Lynne Wong's PhD thesis

Figure 4.4. Fibre samples drying in the Gallenkamp vacuum oven.
Take note of the dish containing silica gel placed below the sample bottles.
A sugar refractometer was used to measure the refractive index of the sucrose solutions
and to convert the readings to dissolved solids (g) in 100 g solution (Brix).
4.6.3 Method for Brix-free water determination in cane fibres
About 3.5 g of the fibre sample was weighed out in three pre-weighed glass bottles of 250
mL nominal size with the stopper on. One served as the sample blank and the other two as
duplicate tests. The bottles without the stoppers were then put in an air-oven at 65 °C for
one hour. During the drying period, the samples were stirred from time to time
(particularly with fine samples such as pith) after which they were dried in a vacuum oven
at 65 °C for 16 hours under 875 mbar vacuum. The bottles were then removed from the
vacuum oven, well stoppered, cooled and weighed to determine the mass of the samples.
To one bottle, about 75 g distilled water was quickly added, followed by the addition of
75 g, 10° Brix sucrose solution to the other two bottles. The mass of the distilled water
and sucrose solution added was accurately determined by re-weighing the bottles.
The bottles were shaken every 10 minutes for one and a half hours to reach equilibrium.
The solutions were then filtered through Whatman 91 filter paper in a funnel which was
covered to prevent evaporation. The first few mL of the filtrate was rejected. The use of a
glass rod with button end helped to squeeze out the solution for filtration (see Fig 4.5).
The Brix of the filtrates together with the original 10° Brix sucrose solution were
determined. For each portion of the filtrate poured into the refractometer, three Brix
readings were taken and an average recorded. Three such averages were recorded after
145