powders and chocolate mass, the determination of the silicic acid
content of the ash is sometimes a necessity, as this facilitates the
detection of any shells which may have been added.[166] The ash ~of
the cacao bean contains~ only between 0·25 and 1·0 percent of
silicic acid, while that of the shell shows on analysis as much as
9 percent; it must, however, be taken into consideration that an
unusually high value for silicic acid in the finished powder might
be caused by impurities in the chemical or other agents used to
effect the disintegration of the cacao. The signs of the presence
of an extraordinary quantity of silicic acid are, according to C.
R. Fresenius (Introduction to quantitative analysis)[167] a higher
percentage of the ash itself than usual, and the quantity of ash used
for the test should not be too small; it should further be remembered
that certain cacao preparations, such as, for instance, the Dutch cocoa
powders, contain large quantities of carbonic mineral matter, and
the special treatment explained by Fresenius when dealing with such
preparations separately should be applied.
4. ~Estimation of alkalis remaining in cocoa powders.~ The ash
obtained from 5 grammes of cocoa powder is washed out of the platinum
pan into an ordinary water glass or tumbler, distilled water only being
used for this purpose, afterwards finely crushed with a glass rod and
heated to boiling point. The liquid is then allowed to settle, filtered
and re-washed. At this stage 5 cubic centimetres of n/1 sulphurous acid
are added, the liquid again heated to boiling point and titrated with
2/n or n/4 alkaline lye. In this way the quantity of added carbonic
mineral matter is determined, in addition to the amount of carbonate
present in ordinary cocoa powders, which is formed from the organic
acid minerals when the ash is produced. Welmans has determined these
values in the commonest varieties of beans and placed the results
obtained at our disposal for the second edition of this book. These
results are as follows:
a) Unshelled roasted beans
===================+========+=========+=========+=========+
| Ariba | Ariba | Caracas | Caracas |
Per cent. | I | II | I | II |
===================+========+=========+=========+=========+
Ash | 4·198 | 4·02 | 7·52 | 4·376 |
Soluble in water | 1·698 | 1·66 | 1·34 | 1·676 |
Insoluble in water | 2·5 | 2·36 | 6·18 | 2·70 |
Alkali (considered | | | | |
as potash) | 0·6417 | 0·6417 | 0·596 | 0·9936 |
===================+===========+==========+=======
| Guayaquil | Trinidad | St.
Per cent. | | | Thomé
===================+===========+==========+=======
Ash | 5·12 | 3·6 | 3·92
Soluble in water | 2·11 | 1·565 | 1·604
Insoluble in water | 3·01 | 2·035 | 2·32
Alkali (considered | | |
as potash) | 0·84 | 1·125 | 0·67
b) Shelled, roasted beans:
====================+========+========+========+=========+=========+
| Puerto | Ariba | Ariba | Caracas | Caracas |
Per cent. |Cabello | I | II | I | II |
====================+========+========+========+=========+=========+
Ash | 3·62 | 3·701 | 3·49 | 3·845 | 3·62 |
Soluble in water | 1·72 | 1·423 | 1·315 | 1·76 | 1·62 |
Insoluble in water | 1·90 | 2·273 | 2·175 | 2·08 | 2·00 |
Alkali (potash) | 0·603 | 0·323 | 0·388 | 0·8725 | 0·4478 |
————————————————————+————————+————————+————————+————————-+————————-+
Alkali in powdered | | | | | |
cacao with 33⅓ | | | | | |
percent of fat | | | | | |
calculated | 0·808 | 0·436 | 0·52 | 1·169 | 0·600 |
Ash, calculated as | | | | | |
above | 4·822 | 4·959 | 4·676 | 5·152 | 4·85 |
====================+===========+==========+========
| Guayaquil | Trinidad | St.
Per cent. | | | Thomé
====================+===========+==========+========
Ash | 3·926 | 3·277 | 3·27
Soluble in water | 1·476 | 1·727 | 1·34
Insoluble in water | 2·45 | 1·55 | 1·93
Alkali (potash) | 0·402 | 0·4209 | 0·4048
————————————————————+——————————-+——————————+————————
Alkali in powdered | | |
cacao with 33⅓ | | |
percent of fat | | |
calculated | 0·54 | 0·594 | 0·542
Ash, calculated as | | |
above | 5·26 | 4·39 | 4·38
These tables show that:
1. The ash of cocoa powder (containing 33⅓ percent of fat) is never
more than 5·5 percent.
2. The maximum amount of alkali (calculated as potash) is 1·2 percent.
3. The ash soluble in water is always less than that insoluble in
water. A reverse proportion shows a larger amount of alkali, that is,
alkali has been added.
In addition to the importance of determining the amount of alkali in
cocoa powder, it is very desirable that analytical chemists should
agree as to the methods to be adopted, since the determinations of
alkali seldom agree and may differ as much as 0·3 percent.[168] The
method of calculating the results should also be defined, that is to
say, an agreement should be arrived at as to whether the alkali should
be expressed as K_{2}O, K_{2}CO_{3} or Na_{2}CO_{3}.[169]
Cacao which has been rendered miscible by means of ammonia, sometimes
contains a small amount of ammonia, probably in combination with an
organic acid. To detect it, the Cocoa powder should be distilled with
water, which gives an alkaline distillate, as the ammonia salt would
be decomposed at the temperature of boiling water. The ammonia can be
volumetrically determined in the distillate with sulphuric acid.[170]
5. ~Determination of the Fatty Contents.~ In this operation 5
grammes of the finest powdered bean i. e. the finest cocoa powder
(in the case of chocolate, which must be finely flaked, 10 grammes)
should be mixed with an equal quantity of evenly grained quartz sand
in a warmed mortar, and then transferred per filter to a Soxhlet’s
apparatus, wherein it can be extracted with ether for from 10 to 12
hours at a stretch. The previously weighed carboy, which now contains
the fatty contents in solution, is placed on a water bath, and the
ether extracted as far as possible, after which the fatty residue
remaining is dried by first introducing the vessel in a water oven
and afterwards allowing it to stand for 2 hours in a dessicator. The
increase of weight in the flask is due to ether extract, consisting
almost exclusively of fat. It is true that small proportions of
theobromine will have been simultaneously dissolved (perhaps about 0·1
g.) but no special significance need be attached to them. If it should
seem advisable to avoid even this slight drawback, petroleum ether with
a boiling point of 50° C. should be employed instead of the ordinary
variety.
Welmans[171] has further described a quick and practical method for
determining fat in cacao and its preparations, which is not only
of value as a check on the extraction method, but also serves as a
determination of the constituents soluble in water. It is carried out
as follows:
5 grammes of Cocoa powder or cacao mass, which need not be very fine,
or 10 grammes of chocolate are stirred for some minutes in a separator
or cylinder with 100 ccm of ether (saturated with water) until coherent
particles are no more visible, that is to say, until the factory degree
of fineness has been attained. In two minutes all will have gone to
powder even if the chocolate has not been rubbed down but is in pieces;
100 ccm of water (saturated with ether) are then added, and the mixture
agitated until a complete emulsion takes place. With powdered cacao,
especially those kinds rich in fat, that occurs in ½ to 1 minute,
and with chocolate in 2 minutes. It is then allowed to rest until
the emulsion separates, which at the ordinary temperature of 15-20°
C. usually occurs in 6-12 hours in the case of chocolate, and 12-24
hours with cacao. The greater part of the water separates first and,
usually, amounts to 90-98 ccm with chocolate and 70-86 ccm with cocoa.
The powdery portion of the cocoa or chocolate floats on the surface of
the aqueous layer at the bottom of the ether layer. Only husk, sand,
particles of cacao beans, added starch, etc. accumulate at the bottom
of the separator and are to be removed with the aqueous layer, which
in the case of chocolate contains the sugar, but usually no trace of
fat. The ether layer, which freely separates from the emulsion in the
time mentioned, is quite clear and from 25 to 50 ccm can generally be
pipetted off and an aliquot part poured into a measuring cylinder or
graduated tube, or into a 25 or 50 ccm flask. If the ether solution
of fat is not sufficient in quantity, the separation can be effected
after removing the aqueous liquid by twirling round the separator.
The turbidity soon disappears and the non-fatty particles quickly
sink to the bottom. The ether solution of fat can also be examined
aräometrically, as with milk fat, by Soxhlet’s aräometric method,
after forcing it by means of an india rubber ball, into a pipette
or burette, but the constants to be used in that case have not been
ascertained. After the ether has been distilled off, in the normal
manner, the weight obtained must be calculated for 100 ccm and a small
correction made. For example, if 50 ccm of the ether solution of fat
give a residue of 0·8 gramme, then 100 ccm represents 1·6 gramme. But
this 1·6 gramme has not been obtained from 100 ccm of the original
(water saturated) ether, but from 100-x ccm, x representing the number
of cubic centimetres corresponding to 1·6 gramme of cacao butter and,
as the specific gravity of cacao butter is nearly = 1; the equation
becomes (100-1·6): 100 = 1·6: x; x = 160/98·4 = 1·627 gramme; so that
the 5 grammes of substance would contain 1·627 gramme of fat or 32·54
percent.
The remaining aqueous solution contains the whole of the constituents
of cacao or chocolate which are soluble in water. It is measured into a
graduated cylinder and its volume ascertained. Then, after the entire
amount has been evaporated to dryness, the residue is calculated on
a percentage basis. The following procedure, however, is preferable.
10 ccm of the liquid are evaporated and the residue well dried in a
vacuum before it is weighed. Multiplying the ascertained weight by
10, we obtain the amount of cacao or chocolate soluble in water and
present in 5 and 10 grammes of either substance respectively. The
amount of ~sugar~ in the aqueous extract can be determined in the
following manner. 50 ccm of the extract are heated in a water bath and
thus separated from ether; afterwards 2 ccm of lead acetate are added
and the whole immediately transferred to a special kind of filter
paper. The solution is now polarised in the usual way and the number
of grammes of sugar thus ascertained converted into ccm by division
(1·55 being the unit) and then the result subtracted from 100, which
gives the volume of water present in 100 ccm of sugar solution, and
so by further division until the percentage of sugar in chocolate is
finally obtained. If the polarisation yields more sugar than the weight
of the total residue, it is an indication that dextrine is present as
an adulteration. The quantitative determination of dextrine, which
is sometimes added to cocoa powder as well as to chocolate, for like
gelatine and tragacanth it holds water together and so ensures a saving
of fat, is best carried out in P. Welman’s polarising method.[172]
As the amount of fat obtained from 5 grammes of a cacao preparation
does not suffice for tests of purity, a larger quantity must be
extracted in order to carry out the following investigations. This has
reference to
1. The determination of the melting point; 2. The determination
of the iodine value (Welman)[173]; 3. The determination of the
saponification value; 4. The determination of the acid value; 5. The
determination of the Reichert-Meissl value; 6. Polen’s value[174]; 7.
Cohn’s investigation[175]; 8. Melting point of the fatty acids; 9.
Refraction of the fatty acids; 10. Iodine value of the fatty acids;
11. Determination of the refractive index at 40° C. in Zeiss’ butter
refractometer.
The following process is usually adopted in the determination of the
melting point of cacao fat:
The melted fat is sucked up a glass capillary tube, the internal
diameter of which does not exceed 2 mm (fluctuating between 1·8 mm
and that measurement) to somewhat above the part of the tube which is
graduated into tenths, and then so much of the capillary tube cut off
as suffices to make the fat column there half the height of the bulb of
the mercury thermometer used in the experiment.
As fresh molten fat has a very variable melting point, it is absolutely
essential that the fat in this experiment be allowed to cool about a
week in some dark chamber, and, because only after the expiration of
this period can the melting point be designated as a constant, not to
proceed with the further determination until this necessary stage has
been reached.
To carry out this determination the capillary tube is attached to the
bulb of the mercury thermometer by means of a rubber ring in such a
manner that the column of fat occurs directly in the middle.
The whole apparatus is now hung in a test tube of 2½ cm internal
diameter, which is just so far filled with water that this can only
penetrate to the fat in the capillary tube which is open at both ends
from the under side. To regulate the flow of heat, this test tube is
further introduced into a beaker also filled with water, which is
heated first. As soon as the fat is melted, the water penetrates to the
capillary tube and pushes along the fat column.
The reading is now taken at once the degree registered, the thermometer
showing the melting point of the fat.
We need not here launch on an exact description of the above mentioned
determination, but will only stay to point out the oft-mentioned book
of R. Benedikt’s, entitled “Analyses of Kinds of Fat and Wax”, as
enlarged and issued by F. Ulzer after the death of the author (Berlin
edition, J. Springer).
Should a doubt arise in comparing the results given by these six
tests, which may happen with some kinds of ordinary cacao butter, the
employment of Björklund’s empirical ether test[176] or Filsinger’s
alcohol-ether test is to be recommended, which latter is carried out as
follows.[177]
3 grammes of cacao butter are dissolved in 6 grammes of ether at 10° C.
Should the resulting solution be clear, this is an indication that no
wax is present. The solution is then introduced in its test tube into
water at 0° C. and the length of the time which transpires before it
begins to become cloudy or to deposit flocculent matter, observed, also
the temperature when the solution again becomes clear.
If the solution becomes turbid before ten minutes have elapsed the
cacao butter is not quite pure. Pure cacao butter becomes turbid in
from 10 to 15 minutes at 0° C. and clear again at from 19-20° C.;
an admixture of 5 percent of tallow renders the solution turbid at
19-20° C. in 8 minutes and it becomes clear again at 22° C.; 15
percent of tallow give a turbid solution in from 4-5 minutes at 0° C. that
becomes clear again at 22·5-28·5 ° C. Filsinger[178] has suggested
a modification of Björklund’s test. In his method 2 grammes of the
fat are dissolved in a graduated tube in a mixture of 4 parts of
ether (S. G. 0·725)) and 1 part of alcohol (S. G. 0·810). Pure cacao
butter should remain clear after some lapse of time, whereas foreign
fats and more especially tallow preparations cause a separation. But
Lewkowitsch[179] maintains that this test is not be relied on, as
genuine kinds of cacao butter will crystallise out from the ether
alcohol solution at 9° C. and some at 12° C.
Yet we are nevertheless of the opinion that liquid fats are of no great
moment at the present time, for they always involve a considerable
lowering of the melting point and so greatly impair the fracture of
the chocolate. Fats such as tallow, or the like, must be used, and
these are detected both by their flavour and by Björklund’s test.
Adulteration is therefore very rarely met with in the German chocolate
industry, thanks to these facts and the rigid self-control practised
by the Association of German Chocolate Manufactures and the sharp
supervision exercised by the inspectors of articles of consumption in
that country. The only regularly occurring adulterations are connected
with the preparation of Cocoa powder and consist in substitutions of
finely ground cacao husk; the detection of which still remains most
difficult and uncertain; and even here it is rather the Dutch firms
which are culpable; and generally speaking it is a trick of smaller
manufacturers, who consider such an admixture as quite the normal
procedure.
6. ~Determination of Theobromine and Caffeine.~ Methods for
the ascertainment of the quantity of theobromine are so numerous
that it would be impossible here to enter into the detail of their
advantages and disadvantages. Of the different processes adopted in
the determination of the cacao diureide perhaps only Eminger’s is
worthy of consideration at present, and this is described fully in the
following paragraphs, as best corresponding to our present knowledge of
the subject and its requirements, and most deserving recommendation to
chemists and food analysts on account of its reliability.
For the practical testing of cacao preparations the splitting up of
the diureide has no special advantage and so we can at once proceed
to treat of the compound particle, though rather inclined to maintain
that the diureide has very little importance on the whole, for it
establishes no basis from which we can judge of the quality of the
various products.
The procedure in Eminger’s process is as follows:
10 grammes of powdered bean of cacao preparation are placed in a
weighed glass flask, then stirred up with 100 grammes of petroleum
ether and allowed to settle. The petroleum ether is next carefully
poured off, without disturbing the sediment, and the treatment repeated
several times. After the last decantation, the residue is well drained,
then dried in the flask and weighed. The difference in weight of the
residue and the former figure represents the amount of fat. An aliquot
portion of the residue (about 5 grammes) is then boiled with 100
grammes of a 3-4 percent strong sulphuric acid in a flask connected
with a reflux condenser, until cacao red is given as a resultant, a
task which occupies three quarters of an hour. The contents of the
flask are then poured into a beaker, and neutralised, whilst hot,
with barium hydroxide. The whole is then mixed with sand in a basin
and evaporated to dryness; afterwards the dry residue is introduced
into a Soxhlet apparatus on a paper cone, and there extracted for
5 hours with 150 grammes of chloroform. The latter is carefully
distilled off and the residue dried for a period of one hour at 100°
C. As previously stated, the separation of the two diureides is not
necessary and in commercial analyses it is sufficient to state the
amount of each separate substance after the removal of fat by means of
some suitable solvent. But should the splitting up be desired, then
Eminger’s method should be adopted, which depends on the solubility of
caffeine in carbon tetrachloride.[180] With that object, the mixture
of fat, theobromine and caffeine is treated in the flask with 100
grammes of carbon tetrachloride and repeatedly agitated for one hour.
After filtration, the carbon tetrachloride, which now contains fat and
caffeine, is distilled off. The theobromine left undissolved in the
flask and the filter used to filter the carbon tetrachloride solution
are then extracted with boiling water, the solution is filtered and
evaporated to dryness, the residue representing theobromine. The
separation of caffeine and theobromine can also be effected by cautious
treatment with caustic soda, so dissolving the theobromine and leaving
the caffeine untouched in its entirety.[181] (Cf. Riederer.)
7. ~Determination of Starch.~ This can only be of importance in
rarer instances, as the starch naturally present in raw cacao generally
varies between 9 and 10 percent, and there is no chemical method of
separating foreign matter from cacao starch. But should the necessity
arise, a determination can be carried out as follows.
In order to render the starch more easily gelatinisable, the fat is
first removed by treating 5 grammes of cocoa powder or 10 grammes of a
cacao preparation with ether and then with an 80% solution of alcohol
to separate any sugar, theobromine and cacao red. The residue is then
mixed with water and subjected to a steam pressure of from three
to four atmospheres, which converts the starch into a soluble body
known as amylo-dextrine. This operation is generally carried out in
an autoclave or strong copper vessel[182] provided with an air-tight
and removable cover, the open flask, containing the sample to be
gelatinised (1 part of cacao and 20 parts of water) being placed in the
vessel half immersed in water.
After screwing on the lid, the temperature of the interior of the
vessel is raised to 133-144° C. corresponding to a pressure of 4
atmospheres, and maintained at that pressure for three or four hours
in order to allow the action to proceed on the mass for gelatinisation
of the starch. The flask is then removed from the apparatus and the
contents allowed to settle for a few minutes; the liquid is filtered
hot, the filtrate amounting to about 250 or 300 ccm after the filter
has been washed a few times with hot water. Only the cell fibre remains
on the filter, whilst the starch is dissolved in the filtrate. This is
now heated with 20 ccm of hydrochloric acid in a flask connected with
a reflux condenser, whereby the starch is converted into dextrose. The
sugar solution is neutralised with sodium carbonate, clarified with
basic lead acetate, any excess of the latter being removed with sodium
sulphate, finally filtered, and the whole made up to 500 ccm. The
sugar is determined in this solution by titration with alkaline copper
sulphate solution and from the number of cubic centimetres required
for the precipitation of the red cuprous oxide, the quantity of sugar
can be ascertained. As 99 parts of starch are equal to 108 parts of
dextrose or grape sugar, the following calculation must be made.
dextrose starch {dextrose}
= { }:x.
108:99 { found }
In the determination of sugar with copper sulphate it is more
advantageous to follow up F. Allihin’s[183] method, in which the
cuprous oxide is reduced by hydrogen gas to metallic copper, weighed
as such, and so the sugar calculated, or the cuprous oxide can be
collected on an asbestos filter and weighed in that condition. The
cuprous oxide must be previously washed with hot water, alcohol and
ether, which must be completely removed by subsequent drying in the
air bath, since an error of even 1 milligramme would seriously affect
the final result. Then again, the amount of sugar may be determined by
polarisation, a process which has also its own particular advantages.
The chemical determination of starch is only in a limited degree
effectual in a recognition of an admixture of foreign starch in cacao
preparations. If more than 10-15 percent of starch, as calculated on
the crude bean, has been found, it must certainly be assumed that there
is an admixture of foreign starch, but chemistry affords no assistance
by which foreign starch may be separated from the genuine starch of
the cacao bean. For that purpose the foreign starch must be observed
under the microscope, which not only serves to detect its presence
but affords a means of estimating the amount present to an approximate
degree, and its characteristics. Great care should be exercised, or the
result may be easily exaggerated. Standard preparations, i. e. which
have a known percentage of starch constituent, prove very serviceable
when comparing.
If Welman’s agitation method has been used for determining the fat,
the starch will be found in the sediment. The amount of foreign starch
can also be determined by Posetto’s[184] method, which depends on the
intensity and permanency of the iodine reaction. In the latter test 2
grammes of the powdered or finely divided cacao preparation are boiled
with 20 ccm water in a test tube for 2 minutes, cooled, and without
disturbing the liquid, 20 ccm of water and 5 ccm of iodine solution
(5 grammes of iodide and 10 grammes of potassium iodide in 100 ccm
of water) are added. The liquid from genuine cacao, according to the
variety used, turns brownish or light blue, changing in a short time
(12 minutes at the most) to brown and red. On the other hand, chocolate
or a cacao preparation adulterated with not more than 10% wheaten or
potato starch, chestnut, maize or commercial dextrine, will give a
blue coloration lasting for 24 hours. It must be noted that the result
in Posetto’s test is influenced by the amount of alkali, so that with
disintegrated cacao, for instance, a considerable quantity of iodine
has to be added before the blue coloration takes place, and this more
especially if the potassium carbonate employed contained caustic
alkali. Such preparations finally become coloured, but generally show a
mixed colour (blue and yellow): green to greenish brown.