This is a point of great importance, inasmuch as it directly influences the result of the analysis of cacao goods. This is especially the case when dealing with cocoa powders, as the test is liable to vary considerably according to the amount of moisture contained in the preparation and the degree of fineness of the powder. In the case of cocoa powders, the sample should be taken repeatedly from a large supply, and from all parts of the material to ensure getting an average sample. The samples taken should be of uniform volume and should, before proceeding to apply the test, be closely mixed together, being, if possible, first passed through a fine sieve. The material ready for the following experiments should then be placed in tin, or better still, glass receptacles with well-fitting corks or stoppers. Paper wrappings or cardboard-boxes are not to be recommended, as the powder is apt to become drier or moister according to the state of the atmosphere to which the packets are exposed.
The most suitable quantity for experimental purposes is, in the case of both chocolate and cocoa powder, as well as butter and covering material, 100 kilogrammes. When determining the amount of foreign fat in cacao preparations, however, as well as estimating the ash content of powder, up to 250 kilogrammes of sample material can be used. In Germany the regulations of the Commercial Agencies of the government public food chemists obtain when sampling and analysing cacao preparations.[162]
b) Chemical Analyses.
The analyses of all cacao preparations from a chemical point of view are conducted, almost without exception, with the object of determining the values for moisture—mineral matter (estimation of the amount of the carbonic acid alkalis and the silicic acid)—fat (estimation of foreign fat)—theobromine and coffeine—sugar—starch (foreign starches)—albuminous matter and raw fibre. The last regulation may also be extended to the estimation of the quantity of shell present.
Estimation of moisture.
1. Estimation of moisture. 5 grammes of material (i. e. fine-crushed chocolate mass) are left to dry (if possible in a double-walled glycerine drying chamber) for about 6 hours at a temperature of 105 Deg. C., the loss of weight of the material being estimated as moisture. The drying should not be continued longer than 6 hours, as fatty material is liable after the expiration of this time to recover some of its weight, owing to the oxygen of the air entering into chemical combination with the fat which rises to the surface or detaches itself from the material. When analysing chocolate, great care should be taken to prevent the mass from melting down and running together at one point. If this occurs, the following treatment must be adopted: A shallow watch-glass is filled with about 10 grammes of sand, well washed and dried, a very fine sand such as so-called sea-sand being preferable to others, the glass then transferred to the drying closet, cooled, and finally 5 grammes of the fine-crushed chocolate added. The mixture is then deposited for a period of 6 hours in the drying chamber, at a temperature of 105 Deg. as indicated above and the weight of the sand deducted when finally calculating the value of the moisture.
If as low a quantity as 5 percent of gelatine has been added to the chocolate, as much as 10 percent of water can be added without in any way affecting the appearance of the material, although such a proceeding is exceedingly detrimental to the taste and durability of the preparation. Such chocolates usually have a dull surface and, if stored in a warm place, are apt to break up and become paler in colour; this result can, however, be prevented by an extra addition of fat. Too high a[163] fat content points in any case of additions of gelatine. P. Onfroy[164] determines the addition of gelatine by boiling 5 grammes of chocolate chips in 50 cubic centimetres of water, adding 5 cubic centimetres of a solution containing 10 percent of lead acetate, and then filtering the whole. If gelatine is present in the chocolate, the liquid, on a few drops of saturated picric acid being added, leaves a yellow, amorphous sediment. If the addition of gelatine is very trifling, the gelatine is held in check or neutralised by the tannic acid. The defatting is then effected by ether and the chocolate stirred up with 100 cubic centimetres of hot water. 5-10 cubic centimetres of a solution of lye containing 10 percent of alkali and about 10 cubic centimetres of the above-mentioned lead acetate solution are added. The compound of gelatine and tannic acid is soluble in the hydrate of the alkali, and is afterwards re-deposited by the action of the lead acetate, so that it can easily be detected by means of picric acid in the neutralised filtrate. As picric acid is incapable of effecting the deposition of the theobromine, the deposition observed can only be caused by the presence of gelatine.
Like gelatine and glue, the addition of a quantity of adraganth has the power of binding the moisture and saving the fat. A method of estimating the quality of this vegetable gum, of which at the most 2 percent should be present, has recently been described by Welmans; this method is explained on page ... in the microscopic section.
Estimation of ash
2. Estimation of ash[165]: 5 grammes of material are heated in a platinum vessel, pan or flat tray, the latter or other similar shallow receptacle being the most suitable, holding from 25 to 30 cubic centimetres. Care should be taken when heating that the extremity of the Bunsen flame only touches the bottom of the vessel. The resulting gases are then ignited, and the completely charred mass pressed or stirred to a powder by means of a platinum wire or rod hammered flat at the end; the pan should be frequently made to revolve and its contents continually stirred during heating, care being taken, too, to hold it slanting the whole time. The pan should be held in this way over a moderate flame until the ash assumes almost a white colour. As soon as this occurs, the pan should be cooled down and the ash uniformly saturated with a concentrated watery solution of carbonate of ammonia, whereon the vessel is placed in the drying chamber and dried at a temperature of 100 Deg. C. The contents of the pan are then heated again very cautiously over the Bunsen flame, care being taken that the bottom of the vessel is only allowed to become red-hot very gradually and to remain so for a very short time; the pan is then covered up and transferred to the dessicator to be cooled, and, on the completion of this process, its weight determined.