THE USE OP A DIELECTRIC MOISTURE METER IN THE SUGAR INDUSTRI 
Introduction, 
The introduction of bulk storage and shipnent of raw sugars 
posed new problems for the sugar technologist. One is the evaluation 
of the keeping qualities of the different sugars, coming from different 
factories, just before unloading in the bulk store. The risk of sugar 
deterioration on storage is very much minimized if sugars with high 
Dilution Indicators are not mixed with others of better keeping qualities. 
The calculation of the Dilution Indicator, or any other safety 
factor for that matter, could not be done on the spot before. The main 
reason was the absence of a quick reliable method for determination 
of moisture in sugars. 
This paper deals with calibration and evaluation of the 
"Kappa" dielectric moisture meter as a rapid and reliable instrument 
for the determination of moisture in raw sugar. It also suggests a 
quick graphical method for the determination of the Dilution Indicator 
of a sugar on the spot. 
Moisture in Sugars. 
The moisture in sugar is mainly incorporated in the molasses 
film surrounding the crystals. This film is composed of a solution of 
sucrose, reducing sugars and some salts. 
The keeping quality of a sugar is primarily a function of its 
moisture content. Hence all the factors suggested to indicate the 
keeping quality of a sugar are based on the percentage moisture in the 
sugar related to some other factor e.g. its solid non-sucrose content 
or the relative humidity of the atmosphere. 
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The three factors 'which are used in the sugar industry are:-
(a) The Safety Factor. 
This has been introduced by the Colonial Sugar Refining 
Company of Australia. It measures the relationship between moisture 
and the non-sucrose content of the sugar i.e. 
Percent Water _ 3afety Pactor. 
100 - Polarization 
(b) The Dilution Indicator. 
This is a modification of the Safety Factor. It measures the 
relationship between moisture and solids not sucrose. It is derived 
from the following equation:-
a. , 100 x Percent Water Dilution Indicator = 
100 - Pol - Percent Water 
(c) The Equilibrium Relative Humidity. 
This relates the moisture content of the sugar as sampled to the 
moisture content of the sugar when at equilibrium with an atmosphere 
of definite relative humidity. This relation gives the Equilibrium 
Relative Humidity of the sugar as termed by Powers. It is considered 
as a measure of the vapour pressure of the surface film and hence 
its osmotic pressure which has probably a major influence upon 
micro-organisms It has also been reported that when a number 
of different raw sugars at different Equilibrium Relative Humidities 
are mixed in the same store, they will interchange moisture in the 
effort to attain equilibrium. Hence with two extremes, one may well 
dry so much that the resulting crystallisation of sucrose in the 
molasses film will cause cementation, whilst the other may absorb 
water and become more vulnerable to microbiological attack 
All the above mentioned factors are ambitious attempts to 
define the density of the molasses film in which no micro-organisms 
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can survive and hence lead to deterioration of the sugars. Control 
of cementation or concretion seems to depend on the uniformity of 
the sugar moisture content and the relative humidity of the atmosphere. 
The accurate determination of the moisture in sugar frequently 
presents great difficulty, and the proper procedure has not yet been 
definitely established. This is because it has been reported that 
moist sugars resist drying with great obstinacy. Raw sugars were also 
( 2 )  
found to be hygroscopic . 
At atmospheric pressure, moisture can be removed only by 
prolonged heating at high temperature. But high temperatures frequently 
exert a destructive effect on the solid sugars. The destructive action 
of a temperature of 100°C is a particularly important consideration in 
the case of fructose and to a less extent in the case of glucose and 
sucrose. Consequently drying methods which combine mild temperature 
and high vacuum are adopted. 
The other disadvantage of the drying methods is the lengthy 
procedure and the long time taken before the results can be found out. 
Wise and Munro^ of I.C.T.A. have already investigated the 
possibility of using the Kappa dielectric moisture meter to measure 
the moisture content of raw sugars• Their work produced premising 
results. Trott and Barrow^ of Barbados substantiated and extended 
Wise's and Munro's work. Prom the results of these -vrorkers it can be 
concluded that the Kappa dielectric moisture meter is capable of 
producing rapid and reproducible results; an attempt to arrive at more 
accurate results by modification of the calibration technique for 
the Kappa meter is described in this paper. 
The "Kappa" Moisture Meter. 
This meter utilizes radio frequencies to measure the change in 
(5) permittivity with moisture content. ' 
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The advantages of the Kappa over other moisture meters are:-
(a) It measures capacitance instead of conductance and hence the 
range of moisture content to -which it is sensitive is wider than 
conductance meters. 
(b) Because it utilizes high frequencies (10 Mc/s), it is more 
sensitive to very low moisture contents than lower frequency meters. 
(c) The high frequencies used help to reduce the erratic effects of 
the ohmic resistence produced by the electrolytes in the molasses 
film of raw sugar crystals. 
(d) The meter is robustly built and easily manipulated. This makes 
it a suitable instrument for routine work in the factory or the 
bulk store. 
(e) The determination of moisture in the sugar sample takes only a 
few minutes by the Kappa meter, once it has been properly calibrated. 
Calibration of the Meter for Raw Sugars. 
The meter measures the permittivity of the whole sample, and 
not that of its moisture content only. Thus the measurement of 
permittivity can be made to serve as a measure of moisture content 
only if the relationship between permittivity measurement and moisture 
content is known. Since this relationship follows no known law, it has 
to be determined experimentally and a calibration curve should be drawn 
for the material in hand. This is rendered easy by the fact that a 
small change of moisture content induces a measurable change of 
permittivity, on the meter dial. The accuracy of the results obtained 
depend mainly on reproducibility of the samples used. The factors 
affecting the meter reading are as follows:-
(a) Uniformity and size of the grains 
(b) The packing degree of the sample 
(c) The ash content of the sample 
(d) The temperature of the sample. 
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To obtain maximum reproducibility of the results, a standard 
procedure was adopted. 
The introduction of the sample to the meter cell followed a 
definite pattern. A sample of 200 grams was poured into the cell; it 
was shaken, then compressed with a well-fitting plunger. This step 
was taken to minimize the packing error as well as to standardise the 
bulk density of the material. 
To annul the error that may be produced because of temperature 
changes, an air conditioned room was used. 
The sugar samples used, were collected from five different 
factories in the out-of-crop season. More samples were bought from 
different groceries. The samples included different types of sugars, 
e.g. export greys, washed greys, local yellows and some refined sugars. 
The errors which arise due to lack of uniformity of grain size 
were not corrected for; they are reported as small ^. 
To reduce the errors produced by large variation in ash content, 
o 
sugars falling within different ranges of one degree pol e.g. 96-97 
were plotted on separate curves. 
In order to draw the calibration curve of the sugar moisture 
content against the sugar Kappa reading, Percent moisture of the sugar 
has to be determined accurately. A vacuum oven operated at 50 mm. Hg. 
and 70°C was used. A triplicate of five gram samples placed in open 
ground cover bottles were left in the oven overnight. The mean percent 
moisture of the three samples was taken as the average percent moisture 
in the sugar. 
Polarization of the sugar was accurately determined, following 
the details recommended by I.C.U.M.S.A. Temperature corrections 
were applied using Brown1 s formula^ 
The experimental data given by those sugar samples acquired from 
factories and groceries, was not enough to give the full shape of the 
Calibration Curves. Very dry sugars and very wet sugars were needed.