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very valuable, for the detection of the adulteration of butter with animal fats, namely, the method of Messrs. Angell and Hehner, based upon the amount in butter and other fats of the fixed fatty acids, and that to the description of which this article is devoted, founded upon the different melting points of butter and all the fats ordinarily employed in its sophistication.

We will now proceed to describe the method of Messrs. Angell and Hehner, above referred to.

Messrs. Angell and Hehner first attempted to estimate directly the amount of the volatile acids contained in butter. They saponified a weighed quantity (usually 3 grammes) in a porcelain basin with caustic potash, frequently stirring with a glass rod. The clear butter soap was transferred to a flask or retort, and decomposed by means of dilute sulphuric acid. This mixture, which contained sulphate of potash, glycerin, and the volatile acids in solution, and the insoluble fatty acids, as stearic, palmitic, and oleic acids, floating on the top, was distilled, and the acidity of the distillate estimated by means of a soda solution of known strength. They found from 4.79 to 7:48 per cent. of the volatile acids in the distillate. The practical difficulties of this method, as the violent bumping of the boiling liquid and the impossibility to obtain a distillate perfectly free from acid, led Messrs Angell and Hehner to adopt a somewhat different and more indirect method of the estimation of the volatile acids. acids are, as we have mentioned, soluble in water, whilst palmitic, 'The volatile stearic, and oleic acids are insoluble. All animal fats, except butter, are mixtures of the glycerides of the three latter acids. Their equivalents being very high and nearly equal, the theory predicted that they would yield, on saponification and decomposition of the soap with dilute acid, nearly equal amounts of insoluble acids. Thus, pure palmitin would yield 95 28 per cent. of palmitic acid; pure stearin, 95.73 per cent. of stearic acid; and lastly, olein 95.70 per cent. of oleic acid. All animal fats, being mixtures of these three glycerides, should, therefore, yield a percentage of fatty acids ranging from 95.28 per cent. to 95.73 per cent., or say, on an average, about 95.5 To prove this theory by experiment, 3 grammes of mutton fat were per cent. saponified in a porcelain basin with a concentrated solution of potash. The saponification was very easy and quick, the liquid boiling quietly. Stirring with a glass rod assists very greatly. The water as it evaporates should be replaced by distilled water, so as to keep the liquid at about from 150 to 200 cc. A perfectly clear soap was obtained, which was decomposed with dilute hydrochloric acid. were fused in the liquid and collected on a previously dried and The fatty acids weighed filter. Before pouring the fatty acids on to the filter, the paper must be well moistened, or some of the fatty acids may pass through it. They were washed with boiling water, dried at 100° C., and weighed. Obtained 95-63 per cent., which figure agrees with the theory.

'Butter, which contains besides palmitic, stearic, and oleic, also volatile or soluble acids, should consequently give a lower amount of insoluble acids, these being diminished in the ratio to the quantity of the soluble acids. A weighed quantity of butter fat was saponified, exactly as was the mutton fat just mentioned. Obtained 86-07 per cent. of insoluble acids, or 9.5 per cent. less than any other fat could have given.' Messrs. Angell and Hehner made numerous estimations of the amount of insoluble fatty acids in butter and other fats, and found the former to yield from 85.40 to 86.20 per cent., whilst the latter gave invariably a quantity approaching very closely the theoretical amount-namely, 95.5 per cent. The average of the results is 85.85 per cent. of fixed acids. The difference between the quantity of fatty acids found in butter and that found in other fats is therefore on an average 9.65 per cent. Mixtures will yield quantities lying between 85.85 and 955 per cent. An adulteration of 100 per cent., i.e. the substitution of any foreign fat for butter, would give a difference of 9.65 per cent.; an adulteration of 10 per cent., therefore, would give a difference of 0.965 per cent. Each tenth of a percentage of fatty acids above the average figure would consequently be equal to 1.036 per cent. of adulteration; but it would be unjustifiable to declare a sample of butter to be adulterated because the fatty acids lie three or four tenths of a percentage above the average figure.'

Messrs. Angell and Hehner have proved the accuracy of their method by mixing butter and foreign fats in known proportions, and estimating the amount of fixed fatty acids. The mixtures yielded invariably quantities closely approximating to the calculated amounts.

Mr. Turner, public analyst of Portsmouth, has suggested the employment of alcohol with a view to hasten the saponification of the fat; this it effects by rendering it soluble and so facilitating and quickening the action of the alkali upon it, the saponification being thereby effected in a few minutes.

About 30 or 40 cc. of spirits of wine are added to the butter in a small glazed porcelain dish, and heated over the water-bath to near the boiling point. About 5 grammes of solid caustic potash are then added, and from time to time a few drops of water to facilitate its solution, the liquid being stirred all the time. In this manner the butter becomes rapidly saponified. The clear, yellowish solution is then freed from all alcohol over the water-bath, and the soap decomposed as already described. Care should be taken to remove all the alcohol, as a small quantity of the fatty acids might be held dissolved should any alcohol remain, and so lead to an erroneous result.

CHAPTER XX.

CHEESE AND ITS ADULTERATIONS.

DEFINITION OF ADULTERATION.

Any foreign substance, animal, vegetable, or mineral, excepting salt and

annatto.

CHEESE consists chiefly of the curd of milk, ripened by keeping, with more or less of the butter and a variable quantity of water.

a

THE MANUFACTURE OF CHEESE.

a

6

The curd is usually precipitated from milk by means of a solution of rennet, which is prepared from the dried stomach of the calf and sometimes the pig.

It may be precipitated by means of acids, but these are rarely if ever employed in this country in the making of cheese ; also by several other substances, as pure curd, old cheese, the natural fluids of the stomach, the first extract of malt and sour leaven. Professor Johnston particularly recommends trials to be made of the pure prepared curd. 'If,' he remarks, ' we are able to rescue the manufacture of rennet out of the mysterious and empirical hands of the skilled dairymaid, and by the use of a simple, abundant, easily prepared, and pure rennet, can command at once a ready coagulation of the milk, and a curd naturally sweet, or of a flavour which we had foreseen and commended, we should have made a considerable step towards the perfection of the art of cheese-making.'

Pure curd may be prepared in the following manner :- Heat a quantity of milk which has stood for five or six hours; let it cool, and separate the cream completely. Add now to the milk a little vinegar, and heat it gently. The whole will coagulate, and the curd will separate. Pour off the whey, and wash the curd well by kneading it with repeated portions of water. When pressed and dried, the casein will be sufficiently pure for ordinary purposes. It may be made still more pure by dissolving it in a weak solution of carbonate of soda, allowing the solution to stand for twelve hours in a shallow vessel, separating any cream that may rise to the surface, again throwing down the curd by vinegar, washing it frequently, and occasionally

a

boiling it with pure water. By repeating the process three or four times it may be obtained almost entirely free from the fatty and saline matters of the milk.'—* Transactions of the Highland Agricultural Society.'

The following is the modus operandi of rennet: it promotes the conversion of the sugar of milk into lactic acid, which, acting like other acids, occasions the precipitation of the curd, although, as already mentioned in the article on • Milk,' rennet seems to possess the property of precipitating casein independent of the formation of any acid.

It has been objected to rennet that by it a readily fermentable and decomposable substance is introduced into the cheese, frequently causing it to pass into a state of decomposition.

It has been also objected that the stomachs from which it is prepared are often in a dirty and more or less decayed condition, and that the strength of the rennet made is very uncertain.

In order to obviate these latter objections the preparation of a solution of rennet, of standard and ascertained strength, has been suggested ; salt, etre, and other additions being made to ensure its preservation. Such a solution would appear to possess several advantages.

The proportions of casein and butter in cheese vary with the kind of milk from which the cheese is made ; thus skim milk cheese is much poorer in butter than that made from cream or whole milk.

Cheshire cheese is of course made from whole milk; Stilton from cream ; while cream cheese consists of the fresh curd of whole milk.

The salting of cheese may be effected in several ways; the salt may be added direct to the fresh curd, and this is the method usually practised in Scotland; or the newly made cheese may be immersed in a solution of brine; or the surface may be rubbed with dry salt—these methods are practised in Cheshire; or, lastly, the salt may be added to the milk previous to the precipitation of the curd. By this method the curd is very equally salted, but the quantity of salt required is very large, the greater part of it being retained in the whey.

The curd, before being compressed, is cut into small pieces so as to allow the whey to drain off; it is then placed, after being salted, in the moulds, a heavy weight being put upon it, but in some cases it is subjected to the progressive action of a screw press.

It is kept for some time in a cool place until it has undergone a kind of fermentation, whereby it acquires the peculiar flavour and the properties of cheese.

The changes which take place during the ripening process have not yet, we believe, been satisfactorily determined; but some interesting particulars will be found recorded in Pelouze and Frémy's Traité de Chimie'—their accuracy may in some particulars be doubted, and assuredly they need confirmation. It appears, however, certain that leucin, butyric, caproic, caprylic, capric, lactic, and valerianic acids, together with ammonia, are generated, the acids combining with the

G G

alkali to form salts. It is stated that as much as 21 per cent. of these ammonia salts have been found. The ammonia is doubtless derived from the decomposition of a portion of the casein.

THE COMPOSITION OF CHEESE.

The following analyses exhibit the percentage composition of most of the principal kinds of cheese met with in the market. The first series is recently made by the author, the second is by Payen :