Part 97

Water, Casein, Fat, Sugar, Ash, Per cent. Per cent. Per cent. Per cent. Per cent. Cheddar 34.38 26.38 32.71 2.95 3.58 Cheshire 32.59 32.51 26.06 4.53 4.31 Stilton 30.35 28.85 35.39 1.59 3.83 Brie 50.35 17.18 25.12 1.94 5.41 Neufchatel 44.47 14.60 33.70 4.24 2.99 Roquefort 31.20 27.63 33.16 2.00 6.01 Edam 36.28 24.06 30.26 4.60 4.90 Swiss 35.80 24.44 37.40 2.36

Full cream, 38.60 25.35 30.25 2.03 4.07 (mean of 143 analyses)

It is evident that the composition of the cheese will vary with the milk from which it is made and the manipulation to which it is subjected. A good American green cheese made from milk of the composition noted below will have the composition which is appended.

TABLE SHOWING MEAN COMPOSITION OF MILK AND CHEESE MADE THEREFROM. Milk. Cheese. Per cent. water 87.38 36.70 ” ” fat 3.73 34.18 ” ” proteids 3.13 23.44 ” ” sugar, ash etc. 5.76 5.68

From the above it is seen that in full milk cheese the ratio of fat to casein is 1.46: 1, and to solids not fat 1.17: 1. This is a point of some importance in judging the purity of a cheese. When the full milk of a mixed herd is used the percentage of fat in a cheese will always be considerably higher than that of casein.

=511. Manipulation of the Milk.=—When sweet milk is received at the cheese factory, a starter of sour milk is added to it in order to hasten its ripening. When it is thought that the proper degree of acidity has been secured, it is subjected to a rennet test. In this test 160 cubic centimeters of the milk are heated to 30° and mixed with five cubic centimeters of the rennet solution made by diluting five cubic centimeters of the rennet of commerce with fifty cubic centimeters of water. The number of seconds required for the milk to curdle is noted. The observation is facilitated by distributing throughout the milk a few fine fragments of charcoal. The contents of the vessel are given a circular motion and, at the moment of setting, the movement of the black particles is suddenly arrested. If coloring matter be added to the milk, it should be done before it becomes sour. The quantity of rennet required is determined by the nature of the cheese which it is desired to make. For a cheese to be rapidly cured, enough rennet should be added to produce coagulation in from fifteen to twenty minutes, and when slow curing is practiced in from thirty to forty-five minutes. When the mass is solid so that it can be cut with a knife, the temperature is raised to 37°, and it is tested on a hot iron until it forms threads an eighth of an inch in length. This test is made by applying an iron heated nearly to redness to the curd. When the curd is in proper condition threads from a few millimeters to two centimeters in length are formed, when the iron is withdrawn. The longer threads indicate, but only to a limited extent, a higher degree of acidity. This test is usually made about two and one-half hours from the time of coagulation. The whey is then drawn off through a strainer and the curd is placed on racks with linen bottoms in order that the residual whey may escape, the curd being stirred meanwhile. In from fifteen to twenty minutes it can be cut into blocks eight or ten inches square and turned over. This is repeated several times in order to facilitate the escape of the whey. When the curd assumes a stringy condition, it is run through a mill and cut into small bits and is ready for salting, being cooled to 27° before the salt is added. From two to three pounds of salt are used for each 100 pounds of curd. The curd is then placed in the molds and pressed into the desired form. The cheeses thus prepared are placed on shelves in the ripening room and the rinds greased. They should be turned and rubbed every day during the ripening, which takes place at a temperature of from 15° to 18°.

=512. Official Methods of Analysis.=—The methods of cheese analysis recommended by the Association of Official Agricultural Chemists are provisional and are not binding on its members. They are as follows:

Preparation of Sample.—Where the cheese can be cut, a narrow wedge reaching from the edge to the center will more nearly represent the average composition than any other sample. This should be chopped quite fine, with care to avoid evaporation of water, and the several portions for analysis taken from the mixed mass. When the sample is obtained with a cheese trier, a plug perpendicular to the surface one-third of the distance from the edge to the center of the cheese more nearly represents the average composition than any other. The plug should either reach entirely or half way through the cheese. For inspection purposes the rind may be rejected, but for investigations where the absolute quantity of fat in the cheese is required the rind should be included in the sample. It is well, when admissible, to secure two or three plugs on different sides of the cheese, and, after splitting them lengthwise with a sharp knife, use portions of each for the different determinations.

Determination of Water.—From five to ten grams of cheese are placed in thin slices in a weighed platinum or porcelain dish which contains a small quantity of freshly ignited asbestos to absorb the fat. The dish is heated in a water oven for ten hours and weighed; the loss in weight is considered as water. If preferred, the dish may be placed in a desiccator over concentrated sulfuric acid and dried to constant weight. In some cases this may require as much as two months. The acid should be renewed when the cheese has become nearly dry.

Determination of Ether Extract.—Grind from five to ten grams of cheese in a small mortar with about twice its weight of anhydrous copper sulfate. The grinding should continue until the cheese is finely pulverized and evenly distributed throughout the mass, which will have a uniform light blue color. This mixture is transferred to a glass tube having a strong filter paper, supported by a piece of muslin, tied over one end. Put a little anhydrous copper sulfate into the tube next to the filter before introducing the mixture containing the cheese. On top of the mixture place a tuft of ignited asbestos, and place the tube in a continuous extraction apparatus and treat with anhydrous ether for fifteen hours. Dry the fat obtained at 100° to constant weight.

Determination of Nitrogen.—The nitrogen is determined by the kjeldahl method, using about two grams of cheese, and multiplying the percentage of nitrogen found by 6.25 for proteid compounds.

Determination of Ash.—The dry residue from the water determination may be used for the ash determination. If the cheese be rich in fat, the asbestos will be saturated therewith. This may be carefully ignited and the fat allowed to burn, the asbestos acting as a wick. No extra heat should be applied during this operation, as there is danger of spurting. When the flame has died out, the burning may be completed in a muffle at low redness. When desired, the salt may be determined in the ash in the manner specified under butter (=498=).

Determination of Other Constituents.—The sum of the percentages of the different constituents, determined as above, subtracted from 100 will give the amount of organic acids, milk sugar etc., in the cheese.

=513. Process of Mueller.=—The process of Müller, as modified by Kruger, is conducted as follows: About ten grams of a good average sample of cheese are rubbed in a porcelain mortar with a mixture of three parts of alcohol and one part of ether. After the mixed liquids have been in contact with the cheese five or ten minutes they are poured upon a weighed filter of from fifteen to sixteen centimeters diameter, and this process is repeated from one to three times, after which the contents of the mortar are brought upon the filter. The filtrate is received in a weighed flask, the alcohol ether driven off by evaporation and the residue dried. Since it is difficult to get all the particles of cheese free from the mortar, it is advisable to perform the above process in a weighed dish which can afterwards be washed thoroughly with ether and alcohol and dried and the amount of matter remaining thereon accounted for. The residue remaining in the flask after drying is treated several times with pure warm ether, and the residue also remaining upon the filter mentioned above is completely extracted with ether. The dried residue obtained in this way from the filter plus the residue in the flask which received the filtrate, plus the amount left upon the dish in which the cheese was originally rubbed up, constitute the total dry matter of the cheese freed of fat. All the material soluble in ether should be collected together, dried and weighed as fat.

By this process the cheesy mass is converted into a fine powder which can be easily and completely freed from fat by ether, and can be dried without becoming a gummy or horny mass.

For the estimation of the nitrogen, about three grams of the well grated cheese are used and the nitrogen determined by moist combustion with sulfuric acid.

For the estimation of ash, about five grams are carbonized, extracted with water, and the ash determined as described below.

Char from two to three grams of the substance and burn to whiteness at the lowest possible red heat. If a white ash cannot be obtained in this manner, exhaust the charred mass with water, collect the insoluble residue on a filter, burn, add this ash to the residue from the evaporation of the aqueous extract and heat the whole to a low redness till the ash is white.

=514. Separation of Fat from Cheese.=—It is often desirable to secure a considerable quantity of the cheese fat for physical and chemical examination without the necessity of effecting a complete quantitive separation. In this laboratory this is accomplished by the method of Henzold. The cheese, in quantities of about 300 grams, is cut into fragments about the size of a pea and treated with 700 cubic centimeters of potash lye, which has previously been brought to a temperature of about 20°. The strength of the lye should be such that about fifty grams of the caustic potash are contained in each liter of the solution.

The treatment is conveniently conducted in a wide neck flask and the solution of the casein is promoted by vigorous shaking. After from five to ten minutes, it will be found that the casein is dissolved and the fat is found swimming upon the surface of the solution in the form of lumps. The lumps of fat are collected in as large a mass as possible by a gentle shaking to and fro. Cold water is poured into the flask until the fat is driven up into the neck, whence it is removed by means of a spoon.

The fat obtained in this way is washed a few times with as little cold water as possible in order to remove the residue of potash lye which it may contain. Experience shows that the fat by this treatment is not perceptibly attacked by the potash lye. In a short time, by this procedure, the fat is practically all separated and is then easily prepared for chemical analysis by filtering and drying in the manner already described (=283=). The fat may also be separated, but with less convenience, by partially drying the sample, reducing it to a finely divided state and applying any of the usual solvents. The solvent is removed from the extract by evaporation and the residual fat is filtered and prepared for examination as usual.

=515. Filled Cheese.=—The skim milk coming from the separators is unfortunately too often used for cheese making. The abstracted fat is replaced with a cheaper one, usually lard. These spurious cheeses are found in nearly every market and are generally sold as genuine. The purchasers only discover the fraud when the cheese is consumed. Many of the States have forbidden by statute the manufacture and sale of this fraudulent article. Imported cheeses may also be regarded with suspicion, inasmuch as the method of preparing filled cheese is well known and extensively practiced abroad. A mere determination of the percentage of fat in the sample is not an index of the purity of the cheese. It is necessary to extract the fat by one of the methods already described and, after drying and filtering, to submit the suspected fat to a microscopic and chemical examination. A low content of volatile fat acid and the occurrence of crystalline forms foreign to butter will furnish the data for a competent judgment.

When the reichert-meissl number falls below twenty-five the sample may be regarded with suspicion. The detection of the characteristic crystals of lard or tallow is reliable corroborating evidence (=308=).

It is stated by Kühn that the margarin factory of Mohr, at Bahrenfeld-Altona, has made for many years a perfect emulsion of fat with skim milk. This product has been much used in the manufacture of filled cheese which is often found upon the German market.

=516. Separation of the Nitrogenous Bodies in Cheese.=—The general methods of separation already described for proteid bodies (=417-425=) are also applicable to the different nitrogenous bodies present in cheese, representing the residue of these bodies as originally occurring in the milk, and also the products which are formed therefrom during the period of ripening. For practical dietary and analytical purposes, these bodies may be considered in three groups:

(a) The useless (from a nutrient point of view) nitrogenous bodies, including ammonia, nitric acid, the phenylamido-propionic acids, tyrosin, leucin and other amid bodies.

(b) The albumoses and peptones, products of fermentation soluble in boiling water.

(c) The caseins and albuminates, insoluble in boiling water.