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. THE MANUFACTURE OF CHEESE. 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. 6 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 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, saltpetre, 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: Water Fat Casein Ash 30.39 53.99 61.87 40.07 26.53 41.41 32.05 30.31 21.68 35.07 4.79 7:09 98.60 95.74 98.96 99.80 94.15 It thus appears that the composition of cheese is very variable, the variation affecting the whole of its constituents. Of course these differences are explained to a large extent by corresponding differences in the kind and mode of preparation of the cheese, but for cheeses of the same name and character greater uniformity will be found to exist. Thus, for the purpose of determining whether a cheese be pure or not it must first be classified, and it must then be determined whether it is a cream, whole milk, or skim-milk cheese, and whether it is a hard cheese, or soft, like cream cheese. These natural differences in the composition of cheese render it somewhat difficult to deal with the question of its adulteration. Johnston has analysed the ash of two samples of cheese: 1. of hand cheese; and 2, of Swiss cheese. It will be seen that the principal portion of the ash of cheese is made up of chloride of sodium, but it also contains notable quantities of phosphoric acid in combination with lime, potash, and sõda, especially the former. ANALYSIS OF CHEESE. In making an analysis of cheese it is usually only necessary to determine the water, fat, casein, ash, and salt; in some cases, however, it may be desirable to ascertain the amount of sugar and ammonia present. Estimation of water.-2 or 3 grammes of cheese should be cut into very fine slices, and dried on the water-bath in a platinum dish until they cease to lose weight. Estimation of fat.-Next the fat may be estimated in the dried cheese, which should be first transferred to a small flask, by exhaustion with boiling ether. The quantity of fat may be ascertained either by the evaporation of the ethereal solution, or by noting the loss of weight of the dried cheese. It is necessary that the cheese should be thoroughly dry, or the ether will not act upon it. If in any case the cheese be not dry, it should be first moistened with a few drops of strong alcohol, after which the ether will dissolve the fat without difficulty. Estimation of casein. This is estimated with sufficient accuracy by igniting the residue insoluble in ether, and deducting from it the weight of the ash. Another method would be by determining the amount of nitrogen by the ordinary combustion process. Estimation of sugar.-The only cheese which contains any appreciable quantity of sugar is cream and other soft cheeses, and this may be extracted from the residue after the removal of the fat by means of ether, by treating first with strong alcohol and then with boiling water. Estimation of ash.-This may be obtained either by incinerating a quantity of the cheese itself, or in the manner above referred to. If it be desired to estimate the amount of salt in the ash, the usual estimation of chlorine by means of a solution of nitrate of silver is to be made.. Estimation of ammonia.-About 50 grammes of cheese are thoroughly exhausted by means of repeated additions of boiling water. After filtration the solution, which contains, besides the sugar and chloride of sodium, the ammonia salts of the volatile acids, is transferred to a retort, and rendered alkaline by means of caustic potash, It is then distilled, and in the distillate the alkalinity is estimated by a standard solution of either hydrochloric or sulphuric acid. The volatile acids may be obtained, together with hydrochloric acid, by boiling a portion of the watery solution obtained, as above described, with dilute sulphuric acid. THE ADULTERATIONS OF CHEESE. Colouring with annatto.-We have referred in the article on annatto to the practice of colouring cheese with annatto-a practice which we have shown to be useless, to entail some unnecessary expense, and, in consequence of the adulteration of annatto with injurious substances, to be attended in some cases with risk to health. Other colouring matters are, however, sometimes employed for the same purpose as annatto; namely, mangold flowers, saffron, and the juice of red carrots; but most of the paler-coloured and all the highcoloured cheeses derive the whole of their colour from annatto. Stilton and Cheddar cheese are never coloured in any way. It may be objected to the whole of these substances that their employment serves no useful purpose. Flavouring with herbs.-Various articles are likewise added to cheese to flavour it, and to impart a green or diversified colour. "In some dairies, the leaves of sage, parsley, and other herbs, are infused into cheese to give it a green colour. In other dairies part of the curd, when ready for the press, is exposed in a sieve to the air, in order that it may become oxygenated, and may render the cheese into which it is mixed with newly prepared curd, of a diversified colour, and of a disposition to run speedily into putridity. In a few dairies rapid putridity is induced by an intermixture of beaten potatoes. In Ross-shire, cheeses are for several days buried within seamark, in order that they may acquire a blue colour and a peculiar taste; and in France, a considerable quantity of cheese receives an offensive smell, resembling that of a pigstye, from the intermixture of fenugreek.-Rural Cyclopædia. Adulteration with potatoes.-Cheese is made from potatoes in Thuringia and Saxony, in this manner:-'After having collected a quantity of potatoes of good quality, giving the preference to a large white kind, they are boiled in a cauldron, and after becoming cool, they are peeled and reduced to a pulp, either by means of a grater or mortar. To five pounds of this pulp, which ought to be as equal as possible, is added one pound of sour milk, and the necessary quantity of salt. The whole is kneaded together, and the mixture covered up |