If the composition of the Devon cream shows clearly that there is some considerable separation of the caseine, the milksugar follows very closely the proportions one would expect to find from the amount of water; for, taking the average of 4-0 of milk-sugar dissolved in 86-87 of water, we get in the present case Water. Sugar. Water. Sugar. which does not deviate very considerably from the numbers actually obtained-viz., 1-723. Devon cream is of the consistence of a soft paste, and is covered with a skin-like layer of partially dried caseous and fatty matter. This cream is produced by keeping the milk in large pans, at a gentle heat, for many hours. The temperature is always far under boiling point, yet probably sufficiently high to arrest fermentation. This application of a moderate heat during a lengthened time causes the fat to coalesce and rise more rapidly than the ordinary method. Such cream is preserved in some degree from the infection of the lactic ferment, and will keep perfectly sweet many days, even in warm weather, provided always that the layer on the top is not destroyed nor disturbed; as when once this is done, especially if the top portion be mixed thoroughly with the rest, lactic fermentation is very rapid. Ordinary, or raw cream, is either cream raised in the ordinary way, that is, by allowing the milk to rest undisturbed at the ordinary temperature; or it is separated by more modern and scientific processes, such as the action of cold and centrifugal machines. Cream, as thus produced, is a thickish, yellowish liquid, containing a variable amount of milk-fat, ranging from 12 to 50 per cent. As a rule the "solids not fat" hold in cream the same ratio to the water as in milk; and similarly the ratios between the caseine, albumen, and ash are but little disturbed, the caseine, as already remarked, being in slight excess. The results of thirty-six analyses of cream by various chemists are thus summarised by König The analysis of cream presents no difficulty, and is conducted on precisely the same principles as that of milk. A little trouble will be found in drying the cream in order to estimate the water, unless, for this purpose, quantities so small as a gramme are taken. This, spread out in a thin layer on a platinum dish, dries easily enough at the temperature of 100°. Should larger quantities for any reason be taken, it will then be necessary to treat the cream after partial drying with petroleum; extract the fat, and then dry the fat and the "solids not fat" separately-the fat at about 105°, the "solids not fat" at 100°; the loss is then considered as water. Cream can be also readily dried in a vacuum, as in the process given at p. 234. The author has met with artificial cream, made of albumen and ordinary cream, and coloured feebly with what was probably the colouring-matter of the carrot. With a view to detect this fraud, it will be advisable, in every case, to estimate the albumen, since the albumen of milk has a tolerably definite ratio to both the caseine and the water. Thus, in the analysis of milk on p. 278, before the cream was abstracted, the proportion of milk-fat to water was as 68 to 87.55, or 77 to 100 of water; while, in the cream, the fat was in the proportion of 57 to 100 of water; in other words, the values in each case fairly agreed. The ratio of the albumen, also, to the caseine, which in the milk before skimming was 1:4, in the cream was 1:58. In creams made up from white of eggs, &c., these relations by no means hold good; the albumen may predominate above the caseine, or be nearly equal to it in quantity. Great caution must, however, be taken in the using of certificates based solely on high albumen; for it may occasionally be a natural product, although it may well be doubted whether a cow secreting albumen instead of caseine, or in fourfold amount, is not either locally or generally diseased. SKIM-MILK. § 174. Skim-milk is simply milk which has been partially deprived of milk-fat. The processes in use are somewhat various. The old-fashioned method of allowing milk to stand, and then removing the cream from the surface by skimming, is giving place, in large establishments, to centrifugal apparatus, by which a far more perfect separation of the milk-fat is effected. The composition of skim-milk compared with the milk in its original state is well seen in the following analyses by W. Fleischmann : Thus, by the operation the proportion of "solids not fat" has been somewhat raised, and this is constantly observed, so that the Public Analysts Society's limit of 9 per cent. of "solids not fat" is a trifle too low for skim-milk; that is, a slightly watered milk, when skimmed and sold as skim-milk, might be found up to the standard. CONDENSED MILKS. § 175. A variety of "condensed milks" are found in commerce, of which the majority are simply milks dried in vacuo at a moderate temperature, then heated up to 100°, in order to destroy mould, and mixed with cane-sugar. There are also concentrated or condensed milks without any addition of sugar or other substance. The analysis of condensed milks differs in no respect from that of ordinary milk, save that it will be absolutely necessary to estimate the milk-sugar by copper, and then to calculate the cane-sugar either by difference or in the way given at p. 262. Unless the cane-sugar is estimated, it is not possible to calculate the amount of concentration to which the original milk has been subjected. This calculation is made by dividing the milk "solids not fat" by 9, or the amount of "solids not fat" present in ordinary milk. It is better to take this number than the higher estimate of 9.2 or 9.3;* for, in the majority of instances, it is certain that there is some decomposition and loss of the milk solids during the evaporation. The ash of the milk should also be carefully examined for alkaline carbonates. If these are present, then the probability is that an impure ash-containing cane-sugar has been employed, and if so, an exact conclusion as to the concentration of the milk cannot be arrived at. The following table gives some analyses of condensed milks, with their amount of concentration, the latter being determined by dividing the "solids not fat" column, as just stated, by 9: * In the original analyses by Mr. Hehner, quoted in the table, he appears to have divided by the higher number-viz., 9.3. * Dingler's Polytechnisch. Journal, bd. 198, § 168. + Pharm. Central. Halle, 1871, No. 35. + Analyst, vol. iv., 1879, p. 44. § American Chemist (2), vol. ii., page 25. || Milchzeitung, 1872, pp. 93 and 179. It is obvious that by the use of the last column, the proper quantity of water to add to the condensed milk, in order to produce ordinary cows' milk, is at once seen. Thus (taking the first milk in the table), since a sample of Anglo-Swiss milk was concentrated 2.96, a pound of such milk would, by the addition of water, have to be made up to 2.96, or very nearly 3 pounds. It will be a question for the analyst to consider whether, in view of the misstatements as to the concentration of the milk to be found on many labelled tins of condensed milks, such assertions are not in their nature misleading, and whether they do not, therefore, come under the Sale of Food and Drugs Act. KOUMISS. § 176. Koumiss is an alcoholic drink made by the fermentation of milk; it is prepared by the nomad population of Asia (especially by the Tartars) from the milk of the mare and that of the camel: it is also manufactured from cows' milk. The preparation of koumiss by the Tartars is very simple: ten parts of fresh warm milk, with a little sugar, are added to one part of milk which is already sour-that is, which contains lactic ferment-and the whole is allowed to rest for two or three hours with repeated stirring. The chemical changes taking place seem to be a partial decomposition of the sugar into lactic acid, the development of carbon dioxide and alcohol, and possibly certain changes in the albuminoids, changing them partly into peptones. The composition of koumiss, since it may be derived from such different sources, is variable. A few analyses are as follows:: In the koumiss from cows' milk, Fleischmann separated 166 per cent. of glycerine. |