Chapter I · DAIRY PRODUCTS

MILK

Milk is adulterated by watering, removing the cream or by adding some foreign substance. Formaldehyde, boric acid or salicylic acid may be added to preserve the milk. Annatto, caramel or some coal-tar dye is added, sometimes to improve the color of the milk, and at other times to cover up traces of watering. Gelatin and starch are added for the same purpose, though they are not frequently used.

ARTIFICIAL COLORING MATTER

Annatto

Add acid sodium carbonate to a sample of the milk until it shows a slight alkaline reaction. Immerse a piece of filter-paper and leave it in for 12 or 15 hours. If annatto is present, there will be a reddish-yellow stain on the paper.

Caramel

Leach’s Method.—Warm 150 cc. of the sample and add 5 cc. of acetic acid, then continue heating it nearly to the boiling point, stirring while it is being heated. Separate the curd by gathering it with the stirring rod or by pouring through a sieve. Press out all the whey from the curd and macerate the latter for several hours (10 to 12 hours) in 50 cc. of ether. It is best to do this in a tightly corked flask, shaking it frequently. If the milk was uncolored or colored with annatto the curd when thus treated will be white. If the curd is a dull brown color caramel was probably used to color the milk. Confirm its presence by shaking a portion of the curd with concentrated hydrochloric acid (sp. gr. 1.20) and gently heating. If the acid solution turns blue while the curd does not change its color, caramel was used to color the milk. (Remember that the ether-extracted curd must be brown.)

Coal Tar Colors

Lythgoe’s Method.—Mix in a porcelain vessel about 15 cc. each of the sample of milk and hydrochloric acid (sp. gr. 1.20) and break up the curd into coarse lumps by shaking gently. If an azo-color was used to color the milk this curd will be pink, but the curd of normal milk will be white or yellowish.

Starch

The presence of starch in milk may be detected by heating a small quantity of the milk to boiling. When it has cooled add a drop of iodin in potassium iodid, and if starch is present there will be a blue coloration.

Gelatin

A. W. Stokes’ Method.—Dissolve 1 part by weight of mercury in 2 parts of nitric acid (sp. gr. 1.42). Add 24 times this volume of water. Mix equal volumes (about 10 cc.) of this reagent and the milk or cream, shake well and add 20 cc. of water. Shake again and, after standing 5 minutes, filter. When a great quantity of gelatin is present the filtrate will be opalescent instead of perfectly clear. To a little of this filtrate in a test tube add the same volume of a saturated aqueous solution of picric acid. If much gelatin is present a yellow precipitate is produced, smaller amounts produce a cloudiness. If the filtrate is perfectly clear gelatin is absent and picric acid may be added without producing any noticeable effect.

PRESERVATIVES

Formaldehyde

Hehner’s Sulfuric Acid Test.—Put 10 cc. of the suspected milk in a wide test tube and pour carefully down the side of the inclined tube about 5 cc. commercial sulfuric acid so that it forms a separate layer at the bottom. A violet coloration at the union of the two liquids indicates the presence of formaldehyde. If the commercial acid is not available, the pure acid may be used, but a few drops of ferric chloride must be added. Sometimes the charring effect of the acid makes it advisable to use the following test:

Hydrochloric Acid Test.—2 cc. of 10 per cent ferric chloride is added to one liter of commercial hydrochloric acid sp. gr. 1.2 (or any quantity in this proportion). To 10 cc. of this mixture add 10 cc. of the milk to be tested. Heat the mixture slowly nearly to the boiling point, in an evaporating dish, but agitating it all the while to prevent the curd collecting in one mass. If formaldehyde is present, there will be a violet coloration. It is said that by this test as small a quantity of formaldehyde as 1 part in 250,000 parts of milk can be detected. It is not so sensitive in sour milk.

Boric Acid

Turmeric Paper Test.—Incinerate some of the milk, and acidulate the ash with a very few drops of dilute hydrochloric acid and afterwards dissolve it in a few drops of water. Place a strip of turmeric paper in this solution for a few minutes, then remove and dry it. If boric acid either free or combined is present, the turmeric paper will be turned to a cherry-red color.

Another way of making this test.—U. S. Dep. of Agr., Div. of Chem., Bul. 65, p. 110: Make strongly alkaline with lime water, 25 grams of the milk, and evaporate to dryness on the water bath. Destroy the organic matter by igniting the residue. Dilute with 15 cc. of water and acidify with hydrochloric acid. Then add 1 cc. of the concentrated acid. Dip a piece of delicate turmeric paper in the solution; and if borax or boric acid is present, it will have a characteristic red color when dry. Ammonia changes it to a dark blue green, but the acid will restore the color.

(Turmeric paper may be prepared by dipping pieces of smooth, thin filter paper in a solution of powdered turmeric in alcohol.)

Salicylic Acid

(This is not often used as a preservative of milk.)

Leach suggests the following method for its detection.—Dissolve one gram of mercury in 2 grams of nitric acid (sp. gr. 1.42) and then add to the solution the same volume of water. Add 1 cc. of this reagent to 50 cc. of the milk to be tested, and shake and filter. The perfectly clear filtrate is shaken with ether and the ether extract evaporated to dryness. Then add a drop of ferric chlorid solution, and a violet color will be produced if salicylic acid is present.

BUTTER

Butter is often colored with annatto, saffron, turmeric, marigold or coal-tar colors. By a certain process, stale or old butter is sometimes worked over and made to appear fresh for a time. This is sold under the name of “process” or “renovated” butter. Foreign fats like cottonseed oil, sesame oil, or oleomargarine may be substituted for or added to pure butter.

COLORING MATTER

Martin’s Test.—Add 2 parts of carbon bisulfid, a little at a time and with frequent shaking, to 15 parts of alcohol. Shake 25 cc. of this solution with 5 grams of the butter, and let stand for some time. The carbon bisulfid dissolves out the fatty matter and settles to the bottom. The alcohol remains on top and will dissolve out any artificial colors that may be present. If only a little coloring matter is present use more of the butter.

Annatto

Evaporate a portion of the extract to dryness and add sulfuric acid to the residue. If annatto is present a greenish-blue color forms. Should a pink tint result the presence of a coal-tar color is to be suspected.

Coal-Tar Colors

These colors will dye wool or silk if pieces of the fiber are boiled in the diluted alcoholic extract, which has first been acidified with hydrochloric acid. The normal butter coloring matter will not dissolve when thus treated.

Geisler’s Method.—To a few drops of the clarified fat on a porcelain surface, add a very little fullers’ earth. If a pink to violet-red coloration is produced in a short time the presence of an azo-color is indicated.

Saffron

When saffron is present, nitric acid colors the alcoholic extract green, and hydrochloric acid colors it red.

Turmeric

Add ammonia to the alcoholic extract, and if it turns brown it indicates the presence of turmeric.

Marigold

Add silver nitrate to the extract, and if it turns black the presence of marigold is indicated.

Process or Renovated Butter

Heat a little of the suspected butter in a spoon or dish, and if it is process butter it will sputter, but not foam much. Make the test also with some butter known to be pure and fresh.

Hess and Doolittle Test.—Melt some of the butter (say 40 grams) at about 50° C. If the butter is pure and fresh the melted fat will clear up almost as soon as it is melted, while the fat of process butter remains turbid for quite a while. After most of the curd has settled, decant as much as possible of the fat. Pour the remainder on a wet filter. Add a few drops of acetic acid to the water that runs through from the filter, and boil. If it was ordinary butter this filtrate will become milky, but if process butter a flocculent precipitate will form.

Oleomargarine

Immerse a test tube, containing some of the filtered fat, in boiling water for 2 minutes. Make a mixture of 1 part glacial acetic acid, 6 parts ether, and 4 parts alcohol. Add to 20 cc. of this mixture in a 50 cc. test tube, 1 cc. of the heated fat which may be transferred by means of a hot pipette. Stopper the tube and shake it well. Immerse in water at 15° or 16° C. Pure butter when thus treated remains clear for quite a while. There will be only a very little deposit after standing an hour, but oleomargarine gives a deposit almost immediately, and in a few minutes there will be a copious precipitate.

When the oleomargarine in butter is in about the proportion of 1 : 10, it will not separate much short of 15 minutes.

Cottonseed Oil

The presence of this oil may be detected by Halpen’s test, which is given under lard, page 60.