Detection of Aldehyde Reductase.-Schardinger Method.*-To 20 cc. of the milk add 1 cc. of a reagent consisting of 5 cc. of a saturated alcoholic solution of methylene blue, 5 cc. of 40% formaldehyde, and 190 cc. of water. Place in a water-bath kept at 45-50° C., and note the time required for decolorization. Lythgoe found that decolorization with raw milk took place in 5 minutes, while with milk pasteurized at 63° for 35 minutes, kept not longer than 2 days, it did not take place in 20 minutes.

FERMENTED MILK.

Yogurt is a Bulgarian product, prepared with a starter known as Maya, which, because of the longevity of the natives who subsist to a large degrce on it, has come to be regarded as a kind of elixir of life. The souring of the milk is caused by Bacillus Bulgaricus which, like domestic yeast and butter starters, is perpetuated by primitive methods, although other bacteria take part in the changes. Cultures of the bacillus in tablet and liquid form are now on the American market with which the beverage commonly known as buttermilk is prepared either by the dairyman or the housewife from milk or skim milk.

The characteristic constituent is lactic acid, both the dextro and levorotary forms, produced at the expense of a portion of the lactose.

Other acid products, similar to yogurt, are Leben of Egypt, Gïoddu of Sicily (Cieddu of Sardinia), Dadhi of India, and Tätté of Scandinavia.

Kumiss is indigenous to Central Asia and the Steppes region of Russia where it is prepared from mare's, camel's, and ass's milk. The alcoholic fermentation is caused by a peculiar yeast that acts directly on the lactose, although bacteria also play a part. With us kumiss is a preparation of cow's milk used chiefly as a therapeutic food, the alcohol being commonly generated by ordinary yeast acting on added glucose or sucrose. In addition to alcohol some lactic acid is also formed from the lactose, the proteins are more or less peptonized or otherwise acted on, butyric acid is liberated, and esters are formed. Dr. L. L. Van Slyke has kindly communicated the following as an average analysis of kumiss made from cow's milk:

Alcoholic beverages similar to kumiss are Kefir prepared in the Caucasus from cow's, sheep's, or goat's milk, using so-called "Kefir grains"

Zeits. Unters. Nahr. Genussm., 5, 1902, p. 1113.

which bear much the same relation to the product as yeast cakes do to bread, and Mazun made in Armenia from sheep's, goat's, or buffalo's milk. Ginzberg * has studied the chemical changes which take place in the preparation of both kumiss and kefir, as well as their imitations.

Analysis of Fermented Milks.-The sampling requires special care owing to the more or less curdled or granular condition. Lumps of curd may be rubbed through a sieve while lumps of fat, such as occur in buttermilk, may be strained out, weighed, and separately analyzed. In special cases the whole sample may be neutralized with ammonia, taking account of volumes.

Total Solids, Total Protein, Casein, Albumin, Other Nitrogenous Constituents, Lactose, and Ash are determined by the methods described under milk with such minor modifications as the nature of the substance may require. For example the casein, already partially or completely precipitated, requires only a small addition of acetic acid, if any. Again since lactose is present in only small amount, a correspondingly larger quantity of this milk may be polarized.

Fat is best extracted by the Röse-Gottlieb method after neutralizing the free acid. Obviously ether extraction of the acid material whether or not evaporated to dryness would yield fat contaminated with lactic acid. Centrifugal methods should be employed only when checked against the standard method.

Total Acids are titrated directly using phenolphthalein as indicator. Volatile Acids and Alcohol are distilled together and the former titrated; the slightly alkaline liquid is then redistilled and the alcohol determined.

CONDENSED MILK.

Canned condensed milk has become a very important article of food, its use having increased greatly during recent years. The universally accepted meaning of the term "condensed milk" in the United States is milk both condensed and preserved with cane sugar, being what is commonly known in England as "preserved milk." The unsweetened variety is termed "evaporated milk" and sold as such.

Condensed Milk, or more properly sweetened condensed milk, is prepared by adding cane sugar to whole milk, usually with previous pasteurization, and evaporating in a special form of vacuum pan to a thick consistency. A considerable quantity is sold to large consumers in bulk,

* Biochem. Zeits., 30, 1910, pp. 1, 25.

in which form it keeps indefinitely by reason of the large percentage of sugar, but for domestic use it is commonly packed in hermetically sealed cans.

Composition.-Various standards committees agree in placing 28% of milk solids and 8% of fat as the minimum limits. As Hunziker has noted manufacturers are not likely to allow their products to drop below 28% of milk solids as that percentage is essential for holding the sugar in suspension without which the product would not be readily marketable. Not infrequently, however, the percentage of fat falls below 8% indicating that skim milk or an abnormally poor product was used. As at no time during the process the heating is carried on at a high temperature, the evaporation may be continued until the percentage of milk solids is raised to considerably over 30% without danger of curdling.

Upward of 350 samples, representing 110 brands, were analyzed in full by the Massachusetts State Board of Health in the course of eight years. As some of the samples were obviously prepared from partially or wholly skimmed milk, maximum, minimum, and average figures have no significance in judging the composition of the genuine product, but the selected analyses of a few typical brands given in the following table are instructive:

High fat, low milk sugar...
Low fat, high milk sugar,
low proteins.
Normal constituents
throughout

Condensed from skimmed
milk

Condensed from centrifugally skimmed milk.

79.17

20.83 31.32 47.85 68.70 32.30 30.27 38.43

7.95 12.00 1.80 4.60 10.70 11.46 1.73 5.63

9.57
6.38

11.97

69.30 30.70
74.29 25.71 32.37 41.92

8.46 10.65 1.29 4.56 69.30 30.70 29.15 40.15 11.89 12.15 3.06 2.05 I. II 69.06 30.94 25.88 43.18 11.55 11.78 0.09 2.46 Trace

Evaporated Milk, or unsweetened condensed milk, formerly erroneously branded evaporated cream, differs from the sweetened variety in that it does not contain added sugar and therefore must be marketed in sterilized form if not required for immediate use.

Formerly 28% of milk solids containing at least 27.5% of fat was required but careful investigations by Patrick, Hunziker, and others showed that it was impracticable to comply with this standard in all regions and at all seasons, without the milk curdling. At present 25.5% of solids and

7.8% of fat (the latter percentage being of the evaporated milk and not of the milk solids) are recognized as the minimum limits regardless of conditions.

Mohan states that swells, flat sours, and sweet curdling are due to understerilization, while other forms of curdling are due to the action of heat on milk with high solids and acidity, and the hard granules sometimes found at the bottom of cans, chiefly to calcium phosphate precipitated by over evaporation.

Composition. The following typical analyses made at the Massachusetts State Board of Health are selected from about 30 representing 8 brands:

High in fat

Low in proteins.

7.02 9.60 I.23 Normal constituents throughout. 28.16 69.24 9.85 8.66 8.10 1.55 Condensed from skimmed milk.. 35.17 64.83 13.90 15.37

36.00 64.00 10.65
31.25 86.75 13.40

11.63

4.20

1.70

A summary of analyses of 12 brands found on sale in the State of

Maine during the year 1916 follow:†

McGill gives in the table on page 178 the averages of results obtained during the years 1910 and 1915 on 16 brands collected in Canada:

Adulteration.-Aside from such foreign substances as may be present in the original milk without the knowledge of the manufacturer, such as preservatives and colors, the only common form of adulteration is the use of skim milk, although homogenized foreign fats are sometimes used to make up for the deficiency. Watering, as it entails greater labor in evaporation, would not be practiced by the manufacturer. If the milk furnished him is watered the defect is corrected by evaporation.

* Jour. Soc. Chem. Ind., 34, 1915, p. 109.

† Maine Agr. Exp. Sta., Off. Ins., p. 76.

Lab. Inl. Rev. Dept. Canada, Buls. 208 and 305.

Preparation of the Sample.-Mix the sample thoroughly, best by transferring the entire contents of the can to a large evaporating dish and working it thoroughly with a pestle till homogeneous throughout. Weigh 40 grams of the mixed sample, preferably in a tared weighing-tray for sugar analysis, transfer by washing to a graduated 100-cc. sugar flask, and make up to the mark with water.

Another method is to weigh the can and contents together, remove the contents to a liter flask with tepid water, dry the can, and subtract its weight from that previously obtained. As the weight of the contents varies this method involves more calculation.

Determination of Total Solids.-Gravimetric Method.-Dilute an aliquot part of the mixed solution further with an equal amount of water and pipette 5 cc. of the diluted mixture, corresponding to 1 gram of the sample, into a tared platinum dish, such as is used for ordinary milk, and rinse the pipette into the dish by means of a wash-bottle. Evaporate, dry at the temperature of boiling water and weigh as in the case of milk (p. 119).

The character of the residue should be noted. It should not, excepting in the case of a skimmed milk, be caked down hard and glossy on the

* Conn. Agric. Exp. Sta. Rep. 1904, p. 133.