Lynne Wong's PhD thesis

2.2 THE PHENOMENON OF BRIX-FREE WATER IN DRY LEAF AND ITS
IMPACT ON CANE JUICE QUALITY
On examination of Tables 2.2 – 2.4, it is evident that while green leaves and cane tops
invariably lowered the Brix, pol and sucrose content in mixed juice, the effect of adding
dry leaves would sometimes raise the analytes (marked in bold in Table 2.2), in particular
when their moisture content was below a certain critical value, of about 20% (Table 2.5).
This increase in analytes by dry leaf addition can be explained by the phenomenon of Brixfree
water in dry leaf.
Similar results have been reported by Hemaida et al. (1977) while investigating the effects
of EM addition on cane. They found that with up to 7.5% green leaves, no effect on the
extraction of both mixed juice and sugar was detected, whereas dry trash (7.5%) markedly
increased Brix, sucrose % and glucose % mixed juice by 0.94, 0.37 and 0.80 units
respectively. They attributed these increases to the higher rate of absorption of water than
of sugar by the dry leaves.
The existence of Brix-free water in leafy trash is rarely reported, while that in cane
fibre/bagasse is well known. It is referred to as "Brix-free water" or "hydrated water" in
South Africa and "adsorption water" or "hygroscopic water" in Australia. It is defined as
the water strongly adsorbed onto the cane fibre and, therefore unavailable for dissolving
the soluble components in sugar cane. It cannot be separated from the natural cane fibre
by mechanical means, but only by elevated temperatures; and it is assumed to be 25% on
dry fibre (Anon., 1984).
Prinsen Geerligs (1904) first determined Brix-free water in fibre by contacting dried
washed fibre with a salt solution, allowing it to equilibrate, and then determining the
increase in the concentration of the salt solution. Steuerwald (1912) applied sucrose
solutions instead of salt solutions, and used two methods to measure Brix-free water: a
contact method and a press method.
Experiments were thus conducted to better discern the Brix-free water in dry leaves and its
impact on cane juice quality.
This section examines the effects of dry and green leafy trash on juice extraction, predicts
sugar recovery from the quality of the cane and first expressed juice and determines the
value of Brix-free water in dry cane leaves.
53