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Sugarcane : Measuring Commercial Quality Jim Engelke, Eng elke, Depart Department ment of o f Agriculture Agri culture,, Kununurra. Kunun urra. There are a number of measurements that contribute to assessing the quality of sugarcane: • • • •

pol (su (sucr cros ose) e) per per cent cent in juic juice; e; brix (tot (total al solubl solublee solids solids)) per cent in juice; juice; pol (su (sucr crose ose)) per per cent cent in in cane; cane; brix br ix pe perr cen centt in in can cane; e;

• fibr fibree pe per ce cent; • com comme merc rcia iall cane cane sugar sugar (CC (CCS); S); and and • purity The process of determining sugarcane quality requires several measurements. measurements. The diagram below summarises the process.

The process of determining sugarcane quality requires several measurements. The diagram below summarises the process. Whole cane Shredded Squeezed

Juice (1st expressed juice)

Shredded cane

Brix in juice

Polarimeter reading

Schmidt Reference tables

Sample taken weighed, washed and dried and then reweighed

Pol (sucrose ) in juice (1st expressed juice)

Fibre per cent

Brix in cane = Brix in juice x 100 - (fibre % + 3) 100

Pol (sucrose ) in cane = Pol in juice x 100 - (fibre % + 5) 100

Commercial cane sugar (CCS) = Pol In Cane - 0.5 impurities in cane

Important Disclaimer The Chief Executive Officer of the Department of Agriculture and the State of Western Australia accept no liability whatso ever by reason whatsoever reas on of negligence negl igence or o r otherwi se arising arisi ng from the t he use or rel ease of this th is informati inf ormation on or any part par t of it. it .

For more information visit our web site www.agric.wa.gov.au

Pol (Sucrose) percent in juice Sucrose content is often referred to as per cent pol, with pol being derived from the name of the machine that measures the sucrose content, a polarimeter. A polarimeter works by sending polarised light through a known quantity of sugar juice (for example, a 100 mm or 200 mm column filled with juice) and measuring the rotation of the light after passing through the liquid. Standards have been developed by mixing known quantities of sucrose with water and measuring the light rotation. The resulting rotation figure can then be converted to a figure that estimates sucrose (or pol) per cent in juice. Either a set of conversion tables or a formula can be used to obtain the sucrose per cent in juice. To use the tables the brix, or total soluble solids, in juice must also be known. Brix is measured using a brix spindle, density meter or refractometer. Brix

Walker four roller mill that squeezes juice from the shredded cane

With the fibre percentage it is then possible to calculate percentage brix and sucrose in cane.

19.0

19.5

20.0

20.5

21.0

21.5

22.0

22.5

71

17.16

17.13

17.09

17.05

17.02

16.99

16.95

16.92

72 r e t g 73 e n i m d i r a 74 a e l r o 75 P 76

17.41

17.37

17.33

17.30

17.26

17.23

17.19

17.16

Brix and pol (sucrose) per cent in cane

17.65

17.61

17.58

17.54

17.50

17.47

17.43

17.40

17.89

17.85

17.82

17.78

17.74

17.71

17.67

17.63

There are two steps to calculating the brix and sucrose in cane.

18.13

18.09

18.06

18.02

17.98

17.95

17.91

17.87

18.37

18.34

18.30

18.26

18.22

18.19

18.15

18.11

Cane is squeezed through a series of rollers to extract the juice. The first pair of rollers squeezes a higher 77 18.61 18.58 18.54 18.50 18.46 18.66 18.39 18.35 proportion of the brix and pol than subsequent rollers. Sampling of juice is routinely performed at Table 1.1 Extract of the reference tables for converting polarimeter the first set of rollers. Therefore the first step is to correct the brix and pol measurements in first and bri x readings to a per cent su crose in juice. expressed juice to more accurately represent those of For example, a sample that has a brix reading of 21.0 and a the total juice in cane. polarimeter reading of 75 equates to 17.98 per cent sucrose in juice using the table above. Using the results of mill experiments carried out by Dr G. Kottmann, CSR formulas are used to calculate the brix and The formula to calculate per cent pol in juice is: pol in cane. Per cent pol (sucrose) in juice = The results of these experiments showed that: {-6.517 + (25.3 x PR*) – 0.0118 x (PR x PR) + (2.937 x brix)–– 0.207 x (brix x brix)} / 100 a. For every 100 parts soluble solids (brix) in the first roller juice there are approximately 97 parts in the whole juice *PR = polarimeter reading of cane. Calculating pol in juice is the first step in calculating per cent pol in cane. Therefore multiplying the brix reading in first expressed juice (1EJ) by 0.97 is a better estimate of brix Fibre in cane in the total juice of cane. To calculate the sucrose in cane or CCS a figure for fibre is also needed.

Method for Determining Fibre Percentage at the Sugar Mill Over a period of 24 hours samples are collected immediately after the cane has passed through the shredder. These samples are combined, and a 500 gram sub sample taken. • Sub sample is put through a cutter grinder. • The ground sample is then placed into a fibre machine where it is washed to remove brix (soluble solids) and fine dirt. • The sample is then dried using hot air and weighed. The final weight divided by the initial weight provides a fibre percentage. Example: Original weight of 500 grams, final weight of 75 grams. Fibre percentage = (final weight / original weight) x 100 = (75 / 500) x 100 = 15 %

Sugarcane harvesting in the Ord.

b. For every 100 parts of pol in first roller juice there are approximately 95 parts in the whole juice of cane. Therefore multiplying the pol in first expressed juice by 0.95 gives an estimate of the pol in the total juice in cane. The second step is to account for the fibre percentage of the cane. This is necessary as higher levels of fibre make it more difficult to extract the juice in cane, whereas lower levels of fibre make it easier for the rollers to squeeze out larger proportion of the total juice.

To obtain the values for brix and pol in cane a fibre per cent is required. The fibre per cent is then deducted from a value of 100 (representing all components of cane) then divided by 100. In the case of fibre per cent equal to 15 = 100-15 / 100 = 0.85 Therefore in the case where cane fibre is equal to 15 per cent, the corrected brix and pol (sucrose) in cane values are then multiplied by 0.85.

Aerial view of Ord Sugar Mill owned by Chei l Jedan g, a Korean based company.

Commercial cane sugar (CCS) Commercial cane sugar (CCS) is calculated knowing both brix in cane and pol in cane. CCS was originally known as POCS or pure obtainable cane sugar. CCS provides an estimate of the percentage of recoverable sucrose from cane. Assump tions that are made when calculating CCS include: 25% of the impurities in cane are removed in clarification and the remaining 75% is in molasses. For every 60 parts impurities going to the molasses 40 parts of sugar are also removed. As a result high impurity cane reduces the potential for raw sugar production. Impurities in cane = brix in cane – pol in cane

Ord sugar mill laboratory where cane quality is determined.

Therefore with a fibre equal to 15 per cent we get:

CCS = pol in cane - 0.75 (impurities in cane x 40/60)

Brix per cent in cane = (brix in juice x 0.97) x 0.85 Pol (sucrose) per cent in cane = (pol in juice x 0.95) x 0.85

Which can be reworked into a simpler equation as follows:

The formulas are expanded in the following calculations.

CCS = pol in cane – 0.5 impurities in cane

Brix per cent in cane

Therefore from the example;

Brix in cane = brix in 1 e J x (100 – (% fibre + 3))/100

CCS = 14.38 - (0.5 x 2.84)

Therefore with brix in juice of 21.0 and fibre of 15% it is possible to calculate brix in cane. Brix in cane = 21.0 x (100 – (15 + 3))/100 = 17.22

= 12.96

Purity of cane Cane purity is a measure of the level of sucrose present in cane relative to the total level of soluble solids.

Pol (sucrose) per cent in cane

Purity is generally expressed in percentage terms.

Pol in cane = pol in 1 e J x (100 – (% fibre + 5)/100

Purity of cane = (pol in cane/brix in cane) x 100

Therefore with our brix reading of 21.0, the pol in juice calculated to be 17.95 and fibre of 15% it is possible to calculate pol in cane.

Purity of cane = 14.38/17.22 x 100 = 83.5 %

Pol in cane = 17.98% x (100 – (15 + 5))/100 = 14.38%

741/02 - 200 - 6/2002

ISSN 0726-934X

© Chief Executive Officer of the Department of Agriculture 2002. This material may be reprinted provided that the article and the author(s) are acknowledged. Published by the Department of Agriculture Western Australia, Locked Bag No.4, Bentley Delivery Centre, WA 6983

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