Lynne Wong's PhD thesis
Lynne Wong's PhD thesis Lynne Wong's PhD thesis
CHAPTER 4. BRIX-FREE WATER IN CANE FIBRES As mentioned in Chapter 2 (Section 2.2), natural fibres have associated water, which is separate from the water in the juice and which cannot be removed by mechanical means. This water is generally termed Brix-free water or hydrated water in South Africa, and adsorption water or hygroscopic water in Australia. Brix-free water is present in varying amounts for a particular substance depending on the vapour pressure of water in the atmosphere and the temperature. Prinsen Geerligs (1897) and Steuerwald (1912) studied the change in concentration of solutes dissolved in water brought about by the addition of fibre to the solution. Previous determinations of Brix-free water in cane reported by Steuerwald (1912), Foster (1962, 1963) and Richardson (1970) gave values ranging from 10% to 50% on fibre. 4.1 THE SIGNIFICANCE OF BRIX-FREE WATER IN CANE The existence of Brix-free water in cane and its unavailability for the dissolution of sucrose affect milling control and direct cane (or bagasse) analyses. Brix-free water in extraneous matter, and particularly in dry trash, when present with cane, can inflate the press juice analytes. 4.1.1 Effect of Brix-free water in cane on milling control Brix-free water is characterised as water strongly adsorbed onto the cane fibre and unavailable for the solution of the soluble components present in sugar cane. As a result, it is incorrect to assume that the mass of juice that can be extracted from cane can be obtained by deducting the mass of fibre as found by drying, from the mass of the cane sample from which the juice is extracted. The mass of fibre plus Brix-free water should be subtracted: Mass of juice = mass of cane - mass of fibre - mass of Brix-free water This juice is termed undiluted (or normal) juice and is the juice expressed by the mills or retained in the bagasse corrected for Brix-free water. For purposes of calculation, it has the Brix of the primary juice. The concept of Brix-free water expressed as a percentage of
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. 111
- Page 111 and 112: various components such as stalk fi
- Page 113 and 114: in the presence of dry leaves, if c
- Page 115 and 116: Table 2.17. Moisture content in sug
- Page 117 and 118: CHAPTER 3. SEPARATION OF THE SUGAR
- Page 119 and 120: Table 3.1. It can be seen that the
- Page 121 and 122: Table 3.2. Fibrous physical composi
- Page 123 and 124: R 579 R 570 M 1557/70 M 1400/86 74
- Page 125 and 126: loosen the fibre. The woody core is
- Page 127 and 128: agitate the mixture in the pot, and
- Page 129 and 130: Figure 3.7. Custom-built fibre-pith
- Page 131 and 132: The extraction of fibres starting f
- Page 133 and 134: pre-treatment in a Jeffco cutter-gr
- Page 135 and 136: Figure 3.19. Stalk cake washed free
- Page 137 and 138: not have many dry leaves attached t
- Page 139 and 140: Table 3.5. Masses of cane samples a
- Page 141 and 142: Table 3.7. Masses of cane samples a
- Page 143 and 144: Table 3.9. Masses of cane component
- Page 145 and 146: 3 57.6 126.3 23.7 97.2 31.1 53.8 11
- Page 147 and 148: Table 3.12. Material loss (%) from
- Page 149 and 150: 3.5.3 Fibre/pith ratios in cane com
- Page 151 and 152: Table 3.15. Effect of extraneous ma
- Page 153 and 154: Snow (1974) investigated the season
- Page 155 and 156: from Figure 2.9 that the change in
- Page 157 and 158: Table 3.18. Fibre % cane results by
- Page 159 and 160: 110
- Page 161: (a). Dry leaf (b). Green leaf (c).
- Page 165 and 166: Steuerwald (1912) applied sucrose s
- Page 167 and 168: solution/fibre ratio was lowered fr
- Page 169 and 170: leave some residual moisture on the
- Page 171 and 172: instead of 150 g of 10° Brix sucro
- Page 173 and 174: Table 4.2. Determination of Brix-fr
- Page 175 and 176: Table 4.3. Comparison of Brix-free
- Page 177 and 178: Table 4.4. Results of the determina
- Page 179 and 180: In order to test for homogeneity of
- Page 181 and 182: Table 4.7. Results of the repeat de
- Page 183 and 184: The experiment was repeated with th
- Page 185 and 186: e any residual moisture in the samp
- Page 187 and 188: By means of the same technique, Won
- Page 189 and 190: was still hot. Since the filter was
- Page 191 and 192: value determined could be corrected
- Page 193 and 194: Qin and White’s finding was confi
- Page 195 and 196: A sample size of 3.5 g with 75 g co
- Page 197 and 198: Figure 4.4. Fibre samples drying in
- Page 199 and 200: - One large fibre sample (rind) of
- Page 201 and 202: Table 4.18. Brix-free water values/
- Page 203 and 204: Table 4.20. Brix-free water values/
- Page 205 and 206: 4.7.3 Statistical analysis It is es
- Page 207 and 208: Table 4.23. Analysis of variance (B
- Page 209 and 210: pointing out that at 52 weeks old,
- Page 211 and 212: The crop of R 570 sampled in 2001 w
dry fibre, or a factor, is used in assessing the accuracy of the various variables used in<br />
milling control, to correct the Brix of primary juice to that of juice in cane and so bridge<br />
the gap in the mass balance.<br />
To calculate the Brix of the undiluted juice from the Brix of the first expressed juice, a ‘dry<br />
milling factor’ can be used. This is obtained by periodically operating the mills briefly<br />
without imbibition water, determining the Brix of the first expressed juice and of the mixed<br />
juice so obtained. For example, if they are 20.0 and 19.4 respectively, the dry milling<br />
factor is 19.4 divided by 20.0 = 0.97. It is then assumed that this factor is the relationship<br />
between the first expressed juice and the undiluted juice when imbibition water is used,<br />
and under these conditions, mixed juice is of much lower density. For example, if the Brix<br />
of the first expressed juice is 19.21 in regular milling, the undiluted juice Brix will be<br />
19.21 times 0.97 = 18.63 (Chen and Chou, 1993).<br />
4.1.2 Effect of Brix-free water in cane on direct cane (or bagasse) analyses<br />
Because of the unavailability of the Brix-free water for the solution of the soluble<br />
components present in sugar cane, methods utilising the wet disintegrator technique, e.g.<br />
pol or Brix in cane (or bagasse), produce higher pol or Brix results than would be observed<br />
if all the water present in cane fibre were available for solution of soluble substances.<br />
Hence, in the direct cane analysis of cane (or bagasse) by liquid extraction, practised in<br />
Mauritius, South Africa and all over the world, the concept of Brix-free water should be<br />
taken into consideration in calculations.<br />
4.1.3 Effect of Brix-free water in dry trash on cane quality<br />
It emerges from Chapter 2 (Section 2.2.3) that when the moisture content of dry trash in<br />
particular is below a certain critical value (Brix-free water content), the press juice<br />
obtained in contact with dry trash has a higher concentration in sucrose, Brix and pol. It<br />
was surmised that this occurs because the trash absorbs water in preference to juice during<br />
pressing to satisfy its Brix-free water capacity. This implies that if cane quality is assessed<br />
by the above parameters, the results will be over-estimated.<br />
111
Change language