E.A. SUGAR JOURNAL, CONGRESS AND EXHIBITION NUMBER. 47
Humidity in Relation to Packing and Storage of Sugar.
(Paper by Mr, W. V. BLEWETT, Ceneral Manager, Kynochs, Ltd.) '
By the humidity of the atmosphere is meant, of I n Johannesburg, for comparison, for threc months
course, the moisture or water-vapour present in the of the year the humidity is over 70, from wllicli i t
air. The atmosphere is never free from moisture, ranges down to 42 in August.
and the quantity present is always varying. During The figures vary considerably from day to day,
the worst months of our summer we rightly blame and averages are,-therefore, to some extent mislcad-
ing. The rainfall, of course, affects the figures.
the humidity for the feeling of heaviness and dis-
The relative humidity a t Mauritius, taking again
comfort, which is so common. The warm air from
monthly averages, shows a t Pamplemousses for sevell
the Mozambique current contains often up to eight wonths over 75, with no month below 68-conditions
or nine grains of water in a cubic foot. At the pre-
much worse than a t Durban.
vailing temperature in Durban during the daytime A t Java, again, Ihe figures are during six months
in the summer, the air could hold up to 13 grains (at of the year, over 80 and for the other six montl~s
85 deg. I?. about), but, fortunately for us, the air about 75.
rarely, if ever, contains the full amount of moisture Before discussing how the humi4ity of the atmos-
possible. It has been shown of recent years that if
phere affects stored sugar, i t will perhaps be of
the air is saturated a t 85 deg. F. the temperature of interest to mention how the relative humidity is
the human body rises and fever sets in, but condi- estimated, as no 6oubt in future f a r more rccords
tions approaching these can exist only under abnor- of humidity will be kept than before. The most
mal conditions, e.g., in mines. If the air is saturated
accurate method 02 finding what moisture there is
i t cannot take up any more moisture, and nature's in the air, is to pass a known volume of air slowly
method of maintaining the normal temperature of
through tubes packed with a material such as phos-
the body, by perspiration, is interfered with. I t is
phorus pentoxide, or strong sulphuric acid, which
not the amount of moisture in the air which matters,
absorbs the water in the air. The increase in weight
but rather the ratio between the moisture present a t of the tubes gives the amount of water present ill
a certain temperature, and what the air could contain
the volume of air drawn through. This mcthod,
a t that temperature when saturated. I n Durban we
although very accurate in reliable hands, is cumber-
do not have many days with the relative humidity
some, and takes some hours and a trained man to do
over 80. If the temperature is 85 degrees, the atmos-
one estimation, hence simple instruments, called
phere can hold 13 grains of water in a cubic foot.
A relative humidity of 80 means that 80 per cent. hygrometers, have been devised, which give the r e .
quired information with little trouble. The simplest
of the 13 grains of moisture is present, i.e., 10lh
type of instrument is that in which a bundle of hairs
grains. On a cold, wet day, in London, wrapped in
mist or fog, the air could not hold more than say is connected to a spring which operates a needle.
2V2 grains, i.e., not half as much as we should have
The hairs shorten when clamp, and lengthen in a
in the air during the driest hot wind we are likely dry atmosphere, and the needle is thus movecl over
a scale showing directly the relative humidity. Such
to get a t the coast. The warmer the air, the more an instrument is very handy, but i t needs to be
moisture it can hold before i t becomes saturated,
checked occasionally. The more generally adopted
and, conversely, as the air is cooled, it can no longer
hold so much moisture as when warm, and a point type is the Wet and Dry Bulb Thermometer. Two
similar thermometers are fixed side by side, thc bulb
will be reached on continued cooling when the air
will have to deposit some of the moisture in the form of one being covered with muslin, one end of which
hangs in a small vessel of water. The water is sucked
of mist, dcw or rain.
u p by the muslin, and evaporates off the bulb, thus
Conditions in Natal, from the point of view of the Iowering the temperature of the bulb-the wet bulb,
sugar industry, are by no means as bad as in other i.e., it shows a temperature lower than that shown by
sugar-growing areas, e.g., Mauritius and Java. Over the dry bulb thermometer. On a d r y day the
a number of years, taking the monthly averages, the evaporation is rapid and the difference in tempera-
relatiire humidity in Durban is 75 in February-this ture is greater than on a wet day. Obviously, if the
reduces to 70 by May, and averages 65 for June, air were saturated with moisture there could bc no
July and August, after which it increases steadily evaporation, and both bulbs would be at the same
to 75 in February. The period from September to temperature. The djffer,ence in temperature is,
May shows a humidity above 70. therefore, a guide to the humidity, and a reference
FOR RATIONS at lowest prices, write: Kaffrarian Steam Mill Co., Ltd., Box 349, DURBAN.
48 S.A. SUGAR JOURN-AL, CONGRESS AND EXHIBITION NUMBER.
Humldity in relation to Packing and Storage ~ P S u g a r . "This opportunity arrives as soon as the sugar
to the tables which are supplied with the instrument ccmes in contact with air containing over 70-75
enables the observes to calculate the' relative relative humidity."
humidity. (Prices of various hygrometei:~ vary from This statement of Geerligs agrees well with the
10s. to 40s. in England.) experiments mentioned above.
The effect. of humidity on stored sugar must be On the other hand, the authors (Tempany and dc
looked a t from two points of view :- Charmoy) of a recent Mauritius Bulletin on the
(1) To what extent is the weight likely to be Deterioration of White Sugar during Storage, state
affected. definitely that "White sugar has appreciably greater
hygroscopic power than lower grade sugars."
(2) To what extent is the deterioration in the At Umbogintwini, 15 samples of sugar were taken
sugar due to humidity. and dried till free from moisture, and then exposed
(1) Effect on Weight. to air which could be kept at a required humidity.
Under the new Weights and Measures Act it is In a few hours' exposure at 74 humidity nearly all
laid down that materials generally must, when sold, the sugars had regained their original moisture as
be the nett weight shown on the container. Ob- if there were a definite quantity of moisture which
viously, if the moist sugar is sent up to the Trans- each sugar could rapidly absorb at that humidity.
vaal during the dry season, there will b~:a tendency The drying, therefore, had no effect on the t e n d e n ~ y
to lose weight. I t would be difficult to state exactly of the sugars to absorb moisture when exposed to n
what weight f ould be lost-it will depend on so damp atmosphere.
many factors, e.g., the conditions of storage, but with Again, it was shown that the best mill whites, i.c.,
good mill white sugars the loss in weight would be those with 0.2 per cent. of water, or less, did not gain -
negligible. in weight beyond their original moisture, and thet
Since the subject of this paper was first suggested, treacle sugars rapidly absorbed moisture up to 2 or
tl-ere has not been sufficient time for experiments 3 per cent. below 75 humidity. (See Note A.)
to be carried out to show the loss in weight of pockets I t will be seen, therefore, that the loss in weight
of sugar in an atmosphere artificially maintained for on storing high-class white sugars in a climate which
months a t a low humidity. Several samples of sugar is drier than that of the Natal coast, will not be a
exposed in open dishes were tested to see what loss serious matter, and can be avoided provided correct
or gain in weight occurred. The sugars were mill conditions of storage in Natal are maintained before
whites and, treacles. The results showed that those sending to dry parts of the country. On the other
sugars which had a, low moisture cont'ent absorbed hand, treacle sugars, on being sent to a drier climate,
moisture more slowly than those with a larger amount ~villcertainly lose weight to an appreciable extent,
of moisture. especially if bags ore exposed in small numbers in
places where air is frecluently changed. (See Note B.)
Sugars with moistures of 0.2 per cent. and less,
when exposed a t humidities from 72-;'6, i.e., about (2) Deterioration of Sugar.
A good deal has been written recently by workers
the average humidity in Durban during the summer,
in various parts of the world on the deterioration of
did not gain in weight. (with one exception). White
sugar during storage. In Natal, Professor van der
sugars with moisture over .2 per cent. increased
By1 has already published bulletins on the subject,
steadily in weight at humidities from 72-76, but a t a
but this paper does not deal (except in passing)
humidity of 60-65 there was, with these sugars,
with the micro-organisms, which he and other
no longer any increase in ~veight below 60 there was
a definite loss in weight. These figures are of in- workers have studied. I t is, however, difficult to
separate the consideration of humidity in its effect
terest as qhowing that in high grade -white sugars,
on sucrose, from that of the micro-organisms con-
the increase in weight on storage is slight, a n d if
cerned. Geerligs, in his well-known book on Cane
kept below 70 per' cent. humidity would be practically
Sugar Manufacture, states that it has been agreed
nil. By far the most rapid increase of weight was
in Java that deterioration is due chiefly to moisture.
with a treacle sugar containing 3.8 per cent. mois-
Sugars that had been manufactured under various
ture when received.
conditions were tested by being exposed during the
These results should be compared with those ob- wet season, and it was shown that the presence of
tained by Geerligs and others. Geerligs in his text impurities, the size of the grain and the difference
book states :- in methods of clarification had no effect. The dis-
"We thus find that although pure sugar does not ii~fectionof bags was tried, but was not altogether
absorb moisture, raw sugar is hygroscopic, and how- satisfactory. (Further work on the effect of dis-
e l e r well dried will absorb moisture as soon as it infectants will be found in Prof. van der Byl's
finds an opportunity to do so." hnlletins on South African sugars.)
FISONS' FERT$LISERS, "The Best in the World."-Sole Dlistributors: Kaffrarian Steam Mill Co., Ltd., Box 349, DURBAN.
AND EXHIBITION NUMBER.
9.A. $'CIGAR J O U ~ ~ N ACONGR~~SS
Humidity in relation t o Packing and Storage of Sugar. double walls with an air space between the walls,
As already stated, Geerligs concluded that pure should be used. He adds: "At the same time, the
sugar is not hygroscopic, whereas sugar coated with aclmittance of air should be prevented during tm-
molasses can absorb a considerable amount of mois- favourable weather conditions." To take the latter
ture, and therefore deteriorate. As sucrose must point first, relative humidities are taken daily a t
re-act with water before it can form reducing sugars, Umbogintwini, and the figures for the first three
only when moisture is present can the micro. months of this year may be taken as typical. It will
organims have any effect. be found that during January there were eight days
The recent bulletin on storage conditions in when the humidity was 80 per cent. and over. On
Mauritius deals somewhat fully with the effect of most of these days it was raining, but one often gets
humidity as distinct from that of micro-organisms. a high humidity when there is no rain. I t would
The authors sum up their conclusions as follows:- seem obvious that on these moist days the store
"The cause of cieterioration of white sugars in should be kept tightly closed against the outside
Mauritius is primarily the absorption of moisture atmosphere. There were 19 days when the humidity
from the atmosphere. If such sugar can be protected was 70 and over, end only four days on which the
from absorbing moisture from the air, it will not humidity was 60 or less. For February/March tlicre
deteriorate, but will keep indefinitely. The fact were :-
that organisms capable of causing destruction of Humidity 80 and over . . 5 and 6 days.
sucrose invariably exist in such sugars, is a matter 70 and over . , 1 ,, 17 ,,
of smaller importance, since it is impossible to pro- 60 and less . . 8 ,, 6 ,,
duce commercially absolute sterile sugars under If we may assume that high grade white sugars
existing conditions, and if the moisture content does do not appreciably absorb water below 65 per cent.
not exceed the danger point, they cannot develop. hnmidity, there would be on an average about two
"The question, therefore, of minimising loss of this days a week during these three wettest months of
description consists essentially in protecting sugars, the year when the store could be safely o]lcncd.
as far as possible, from conditions likely to lead Whether or not this is practicable is a matter for
to moisture absorption. 1
I 1 this connection, the storekeeper to settle. It should be pointed out
the construction of warehouses where sugar is in- that Zhe humidity a t Umbogintwini is less than in
tended to be stored is a matter of the greatest Durban (being higher and further from the sca).
importance." From our knowledge of humidity and atmospheric
I t should be borne in mind that nearly all conditions it should be easy to lay down principles
Mauritius sugar is treated with steam in the centri- that should be observed during storage :-
fugal, and may be regarded as nearly sterile as is (1) The store sl~ouldbe built of such materials
possible in practice when it leaves the centrifugals. and in such a way that it is not liable to sudden
In trying to account for the deterioration of changes of temperature. With solid walls and roof,
various sugars, the authors suggest the difference in or with an insulating air space round walls and roof,
the size of the grain, or in the mineral content of the store is not liable to sudden cooling. I t will be
the sugar, herein differing from Geerligs. Their 01,vious that if a store and the air inside it cool
description of the deterioration which takes place quickly at night-time after a warm day, a point may
agrees with their explanation as to the cause of be reached when t h e air can no longer hold its
the deterioration, viz., humidity. I t is noticeable moisture, and the latter will be deposited, and thcn
first by the sweating of the bags of sugar, the sugar later absorbed by the sugar.
itself becoming more and more sticky. This action (2) The floor should be of non-conducting
is invariably from the outside; generally it is con- material, built over an air space, and thus insulated,
fined to the lowest layer of bags, especially to the This tends to prevent moisture being deposited on
side of the bag ir, contact with the floor, or with the floor. Obviousiy, flooring likely to cool rapidly
the dunnage. In localities with a high rainfall, bags will cool the air next to it and cause moisture to bc
which were exposed to air blowing direct from doors deposited. Tempsny and de Charmoy, in Mauritius,
or windows showed deterioration on the exposed ends stated that in a stcre where a floor had been built
or sides. They follow up this statement by a over two large pits there was no deterioration what-
description of a store where no deterioration took ever in six months, although the amount of humidity
place in six months. in that district is niuch higher than at Durban. 111
The question of the construction of stores for this case there was a dead space under the floor of
maintaining the best conditions for the storage of five or six feet. They showed tha't when a layer of
sugar has been raised by various authors, e.g., Prof. insulating material was placed between the sugar
van der Byl, in his Bulletin on the Deterioration of bags and the floor (the matcrial used was volcalzic:
South African Sugars, who suggests storehouses with ashes in half-inch pieces), the sweating of the sugar
FOR RATIONS at lowest prices, write: Kaffr,
arian Steam Mill Co., Ltd., Box 349, DURBAN.
1Yumlditv in relation t o Packing and Storage 0 P S ~ g l l r . Note A.-To test the statement that pure sugars
-was greatly reduced ; and that in a case where sugar are more hygroscopic than raw sugars, three sugars,
was placed on boiler tubes it deteriorated rapidly a No. 1refined, a good mill white, and a treacle sugar,
where in contact with the metal. were taken and exposed in dishes to an atmosphere
These facts are all in accordance with the state- at 90 relative humidity for 48 hours. All three in-
ment that humidity is the prime factor in causing creased in weight, but where the white sugars in-
the deterioration of sugar. creased from 0.1 per cent. to 0.8 per cent., the treacle
(3) Doors and wiildows are only to be opened on sugar absorbed twice as much (from 0.5 to 2.1).
dry days. On days when it is raining, or when the After a further 48 hours, the two white sugars con-
humidity is high, all openings should be tightly tained 2.2 per cent. water, and the treacle sugar 4.2
closed. per. cent.
By placing hygrometers in the vicinity of the store The same sugars (this time in sugar pockets) were
it is a simple matter to avoid unnecessarily exposing exposed to a dry atmosphere for 10 days, the relative
the sugar to atmospheric moisture. humidity being 57. The three sugars lost in weight,
Further, by means of a fan, the air in the store the white sugars losing .04 per cent. moisture, while
could be rapidly changed when the atmosphere out- the treacle sugar lost .3 per cent., i.e., from .5 per
side was dry. Merely opening a store to the dry cent. down to .2 per cent. by the end of 10 days. (It
air is not sufficient without thorough ventilation. should be mentioned that this treacle sugar had been
(4) I t is probable that if the above suggestions previously dried down to .5 per cent.)
were given effect to, it would not be necessary to go Note B.-With regard to the effect of the material
further, and artificially dry the air in the store. On used in packing: Geerligs took sugar already con.
the other hand, where stores, badly constructed, are taining 0.7 per cent. water and stored in or dinar^
already in use, it would be an expensive matter to bags alongside of bags lined with waxed paper. IEe
re-build; in such cases the advisability of drying states that moisture was absorbed in both cases at
the air should be considered. Air can be dried in the same rate-and also when the bags were lined
various ways :- with paper dipped in rubber solution. He concludes
that it is impossbile to modify the packing so that
(a) By cooling it so that it can no longer hold
the absorption of moisture could be prevented. This
the moisture originally present, which is then de-
posited. On re-warming the air it can then take up conclusion is so unexpected that it would seem to
nted confirmation. Natal sugars were, therefore,
more moisture, and so dry the material with which
it is in contact, One method of doing this is to pass stored at a humidity of 70 (average), in various
coverings: the normal bagging material, paper bags,
air through a to~verdown which very cold water
waxed paper bags, and in rubber linings, but thz
runs. This method of drying the air requires a
~esults were not sufficiently concordant to enable on:
to say whether they confirmed Geerligs' statemenl
(b) A more common method is to heat up the air, or not, and the experiments will have to be repeated.
by which means its capacity for holding nloisture is
increased, and here, again, it can remove moisture DISCUSSION.
from materials coiltailling water.
(c) A third method, which is applicable to stores The Chairman, in thanking Mr. Blewitt for his
ill which the air is only occasionally changed, is to paper, referred to Mr. Blewitt's remarkg concerning
use a drying agent. One that is used ill various in- the warm air from the Mozambique Channel, and
dustries is calcium chloride. Air can be drawn over stated that the practical experierice of everyone con-
trays of calcium chloride into a store, and when it nected with the storage of sugar in Durban was that
has taken up as nlcch moisture as is practicable, the at all costs the easterly minds should be avoided, and
moisture is driven off the calcium chloride by heat it was therefore obvious that it was the east winds
and the latter can be again used. 'Without any we have to fear more, so far as the storage of sugar
alterations to a store, trays of calcium chloride can was concerned. The westerly wind did not appear
be placed in it. In a few days the lumps of chloride to affect sugar adversely. The question of the
will have disappeaied aild the trays will become full storage of sugar will have to be faced in the near
of liquid-the chloride having absorbed a large por- future; the present methods were haphazard. Dur-
tion of the moisture in the store, especially if the air ing the last season sugar had been stored in approxi-
is circulated. Provided a store can be kept tight, mately twenty stores in Durban, not half of which
. and the air but occasionally changed, this method has were in any way suited for the purpose.
many points in its favour. I t has already been tried Mr. J. IJ Malcom expressed his pleasur: a1 having
recently in a sugar store in Durban, and those in beard Mr. Blewitt's paper, and statctl t l l ~ ts o ~ l o
charge seem very pleased with the results. J ears ago, when the Government Lzxed sugar they
FISONS' FERTILISERS, "The Best in the .World. "-Sole Dlis tributors: Kaffrarian. Steam Mill Co., Ltd., Box 349, DURBAN.
F.A. SUGAR, JOURNAIJ, CONGRESS llND EXHIBITION NUMBER. 51
were desiroas of arriving a t the amo~mtof loss in ago complaints were received that treacle sugar was
the slorsge of sugar, and the losscs as represented arriving in Johannesburg with a loss in weight.
to the Governnlent were not correct. Sugars that had been in the store for some moiztl~s
Mr. Malcolmn stated that his company took half were then tested,- and were something likc ten to
a ton of sugar from four mills; the moisture contents fifteen pounds over weight.
were taken of that sugar and also the sucrose. The
test lasted six months, and during that period some Mr. Alfred Townsend also spoke on tlze qt~cstion
of the sugar lost very little sucrose and did not gain of the storage of sugar, stating that some tinzc ago
very much weight. Some of it gained in weight with, they had occasioiz
at tlze mill 11e was coiz~iectecl
and lost in sucrose, the reason being that the moisture to store sugar in large quantities, aizd they thcrcfore
in sugar was high and above what is considered a built a store aizd ventilated it well. The result was
safe point. That point, of course, is disputed even disastrous. On the seconci occasion, a t Sea Cow
to-day. There are people who think that sugar with Lake, he and his brother had to store sugar, ancl they
a moisture content of .2 is safe, but he did not adopted the opposite may and had a sealccl store
think it was safe; it has to be a bit drier if it is with tlze result that they had dry sngar. By kcc1,ing
for consumption. ZIe had had refinery sngar in the the atmosphere away from the store no troublc was
store for over a year which had not increased to any experienced so far as sweating mas concerned. Thc
appreciable extent in moisture. Not many months sugars iiz both iizstailces mere iclentical.
Fungi and Bacteria in Sugar and Sugar Came.
(Paper by P. A. VAN DER BIJL, D.Sc,, Professor of Plant Pathology, Stellenboech University,
late Government Mycologist, Durban,)
The sugar industry has during its development The root disease of cane caused by the fungus
passed through various phases. I 1 its early ,history
1 himaiztia stellifem-the stcllate crystal fui~gus-is
man's taste was deemed sufficiently delicate to decide prevalent in Natal and Zululaizd aizd may be rcspoa-
the degree of ripeness or the nature of the cane, but sjble for a poor stsncl of cane and a consequent lcs:;
with the application of science to industries it soon yield per acre.
appeared that chemical tests provided a far more This disease is recognisable to the naked eye by
delicate and certain means for ascertaining the tlze basal leaves of the cane being matted together,
qualities of cane and for controlling milling opera- and if the stool is uprooted, white fungoid tlircads
tions so as to minimise loss. are seen on and between the roots and on old cane
The cane grower and miller have also benefited material decaying ;n the soil. Many of the roots of
from the.application of botanical science to the sugar the stool will also be dead.
industry; on the one side, through the efforts made The fungus responsible for this disease is of the
at increasing the yield of sugar by studying methods nature of a weak parasite, and the amount of damage
of cultivaiion and by selecting and breecling for ~
caused by it is largely depencient on ~ v e a t h ccon-
high sugar contentand other desirable properties, ditions and the nature of cultivation the cane is
and on the other by investigations seeking to control receiving. I
losses occasioned to cane and cane products by those
lniscroscopic plants known as fungi and bacteria. Given good cultivation and nzoderately favourable
' weather conditions, the cane outgro\vs the fungus,
Like the majority of cultivated plaats, sugar cane but under dry conditions and poor cultivatioii tlze
is also subject to a number of diseases of which some cane js handicapped, on the one hand by the poor
zre caused by fungi, others by bacteria, and others cultivation-young buds fincl i t clifficult to fore*
again by constitutional derangements in the normal their may through the lzarcl soil, ancl in their strugglc
!ctivities of the plant, and unfavourable conditions may be killed by the fungus,or other agencies; ancl
of growth. on the othei*hand, by the scaiity amount of moistiirc
We will first briefly refer to some of the diseases s t its disposal. The fungus has also partly killcd
of canc caused by fungi and known to occur in Natal the roots of tlze cane, which is hence not in a position
and Zululand. (No bacterial disease has thus far to get the full benefit from such moisture as may be
been recorded in cane from Natal and Zululand.) still present in the soil.
FOR RATIONS at lowest prices, write: Kaffrarian Steam Mill Co., Ltd., Box 349, DURBAN.