Lynne Wong's PhD thesis

dry fibre, or a factor, is used in assessing the accuracy of the various variables used in
milling control, to correct the Brix of primary juice to that of juice in cane and so bridge
the gap in the mass balance.
To calculate the Brix of the undiluted juice from the Brix of the first expressed juice, a ‘dry
milling factor’ can be used. This is obtained by periodically operating the mills briefly
without imbibition water, determining the Brix of the first expressed juice and of the mixed
juice so obtained. For example, if they are 20.0 and 19.4 respectively, the dry milling
factor is 19.4 divided by 20.0 = 0.97. It is then assumed that this factor is the relationship
between the first expressed juice and the undiluted juice when imbibition water is used,
and under these conditions, mixed juice is of much lower density. For example, if the Brix
of the first expressed juice is 19.21 in regular milling, the undiluted juice Brix will be
19.21 times 0.97 = 18.63 (Chen and Chou, 1993).
4.1.2 Effect of Brix-free water in cane on direct cane (or bagasse) analyses
Because of the unavailability of the Brix-free water for the solution of the soluble
components present in sugar cane, methods utilising the wet disintegrator technique, e.g.
pol or Brix in cane (or bagasse), produce higher pol or Brix results than would be observed
if all the water present in cane fibre were available for solution of soluble substances.
Hence, in the direct cane analysis of cane (or bagasse) by liquid extraction, practised in
Mauritius, South Africa and all over the world, the concept of Brix-free water should be
taken into consideration in calculations.
4.1.3 Effect of Brix-free water in dry trash on cane quality
It emerges from Chapter 2 (Section 2.2.3) that when the moisture content of dry trash in
particular is below a certain critical value (Brix-free water content), the press juice
obtained in contact with dry trash has a higher concentration in sucrose, Brix and pol. It
was surmised that this occurs because the trash absorbs water in preference to juice during
pressing to satisfy its Brix-free water capacity. This implies that if cane quality is assessed
by the above parameters, the results will be over-estimated.
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