CHAPTER XI.

FLOUR AND ITS ADULTERATIONS.

DEFINITION OF ADULTERATION.

Any other added farina than that indicated by the name under which it is

sold ; alum or any other added mineral substance. THE term flour may be applied to the meal or powder obtained by the grinding of almost any species of grain or seed, but we shall treat in the present article chiefly of those descriptions of grain and flour which are most in use in this country as articles of diet, as wheat, rye, oats, barley, maize, and rice.

Each of these flours consists of nitrogenous, non-nitrogenous and mineral elements or constituents; the nitrogenous embrace chietly glutin, or gliadin, fibrin, albumen, casein, cerealin, together with certain modifications of some of the foregoing; the non-nitrogenous are sugar, dextrin, but chiefly starch, fat, and cellulose; the mineral are for the most part alkaline phosphates and silicates, especially phosphate and silicate of potash.

We shall treat of each of the flours above enumerated under separate headings, and first of

WIEAT FLOUR.

There are several distinct species of wheat: that which is chiefly cultivated in this country is the Triticum vulgare; of this there are two varieties—T. æstivum, or summer wheat; and T. hybernum, or winter wheat: the former is sown in the spring, and the latter in the autumn. Of these varieties, again, there are several modifications, into the description of which it is, however, not necessary to enter on the present occasion.

Wheat seeds or grains, as brought to the market, and as supplied to the miller, are deprived of their paleæ, or husks.

The number of parts into which ground wheat is separated, and the amount of each yielded by given quantities, vary according to the characters of the wheat, and the processes adopted by different millers.

In wheats which are hard the integuments separate with difficulty, and therefore the flour produced from these usually contains a greater proportion of adherent bran than do those flours procured from wheats which are soft, and which part with their epidermic coverings more readily.

According to Mr. Hard, a miller of Dartford, in Kent, the following are the products, with the quantities obtained, of one quarter, or eight bushels of ground wheat :

• Produce of One Quarter of Wheat, weighing 504 lbs. Flour

892 lbs. Biscuit, or fine middlings

10 Toppings, or specks

8 Best pollard, Turkey pollard, or twenty-penny Fine pollard Bran and coarse pollard Loss sustained by evaporation, and waste in grinding, dressing, &c.

11

99

15 18 50

99

504 lbs.

COMPOSITION OF WHEAT FLOUR.

We have already enumerated all the more important constituents which enter into the composition of the grain of wheat, and of the flour made therefrom. The grain of wheat differs from that of the other cereals principally in the peculiar physical characters possessed by its chief nitrogenous constituents, and especially glutin, or gliadin; crude gluten being a mixture of this with fibrin, and possessing, as will be seen hereafter, in the moist state, strongly adhesive properties. These are found to be practically of great value in bread-making, causing the dough to retain more strongly the carbonic acid evolved during fermentation, whereby the bread is rendered porous and light; and this is one of the chief reasons why the flour of wheat is preferred for breadmaking to that of all other grains. We shall now describe in detail all the more important, and especially the nitrogenous, constituents of wheat flour. The particulars which will be given relative to these will apply in great part to the other cereals.

Crude gluten.-Crude gluten, as shown below, consists of several substances, and hence its properties partake to some extent of the characters of its constituents.' Although water exerts such an effect upon it in rendering it adhesive and tenacious, yet it is entirely insoluble in that menstruum. When freed from moisture it is tasteless, more or less transparent, and shiny. It is soluble in caustic potash and other alkalies, and is precipitated from its solution by most dilute acids. It is soluble in strong acetic acid. Digested in water containing from one to two thousands of hydrochloric acid, it gradually dissolves, furnishing a liquid which is lævorotatory, and in which the gluten comports itself with heat and reagents exactly as does albumen.

Glutin.— The above remarks apply to the crude gluten, but the pure glutin, gliadin, or vegetable gelatin, in its hydrated condition, fornus a liquid of the consistence of varnish, and which is susceptible of being drawn out into silky-looking threads. When obtained from its alcoholic solution, treated with ether and dried in vacuo, it forms a hard, britile, and opaque mass. When simply evaporated from its alcoholic solution, it resembles in its physical characters animal gelatin.

Glutin is soluble in dilute alcohol of from 40 to 80 per cent., but only with difficulty in absolute alcohol, from which it is deposited in the form of a white powder. It is only very slightly soluble in cold, but more freely in hot water, the solution yielding precipitates with gallotannic acid, basic acetate of lead, and several other metallic salts. With ferric sulphate, mixed with ammonia, it gives an orange-coloured or brownish precipitate, in which respect likewise it resembles animal gelatin. It dissolves, giving rise to a blue colour, in hydrochloric acid ; in nitric acid it also dissolves, but is again precipitated on the addition of water. It is entirely soluble in tartaric and acetic acids, but only partially so in phosphoric acid. It is also soluble in the fixed alkalies, less so in ammonia, and the alkaline solutions afford precipitates with metallic and some other salts. With mercurous nitrate it gives rise, in the moist state, to a bright red colour; with strong sulphuric acid and sugar, to a yellow colour, which after halfan-hour hanges violet.

The following is the composition of pure glutin, according to Ritthausen:Carbon

52:49 Hydrogen

6.97
Nitrogen

18.02
Oxygen
Sulphur
Ash

.

21:41
0.85
0.26

.

It would appear that the albuminous substances entering into the composition of crude glutin have really nearly the same percentage composition as the other albuminoids. "Gündsberg states that glutin, or gliadin, is not a simple proximate principle, for cold water extracts from it a brown substance containing nitrogen and sulphur, while the residue, treated with boiling water, yields a solution which on cooling furnishes a substance free from sulphur, which has nearly the same composition as animal gelatin, and which Gündsberg regards as the true glutin, or vegetable gelatin.

Fibrin.—This is the portion of crude glutin of wheat and other cereals which is insoluble in alcohol. In its moist state it forms a greyish-white elastic mass, but when dry a horny substance, which recovers its former characters by maceration in cold water. It is soluble in acetic, hydrochloric, and phosphoric acids; also in the alkalies, including ammonia, and is precipitated from these solutions on neutralisation. Acording to Scherer, fibrin contains 15.8 per cent. of nitrogen. Later analyses correspond in the main with the foregoing, but in three analyses made by Dumas and Cahours the nitrogen varied as follows:-15-8, 16:0, and 16.4.

It undergoes gradual alteration in contact with moisture, is transformed during germination, giving rise in the case of wheat and other cereals to the formation of diastase.

Casein,-frequently called legumin, is found abundantly in the seeds of the leguminosæ, and in small amount in wheat and other cereals. When dried from its alcoholic solution it is of a greyish-white colour, and readily reducible to the state of powder. It is soluble in boiling alcohol and in cold dilute acetic acid, but it becomes insoluble under certain circumstances, as when precipitated by ammonia from its solution in acetic acid, when boiled for a short time with water, or even when left in contact with it or with dilute alcohol.

Albumen.—The albumen deposited by heat from vegetable solutions is usually in the crude state, and is contaminated by colouring matter and other substances. For its purification the precipitate must be washed with water, and then with boiling alcohol and ether. Its solution coagulates at from 61° to 63° C., and at a little higher temperature is converted into a solid mass. If the solution is very dilute, the albumen is deposited in flocculi. Albumen thus coagulated is white, opaque, and elastic; when dried it is of a yellow colour, brittle, and translucent. After having been dried, it absorbs water when immersed in it, and assumes its original characters, and if dried at a temperature below the point of coagulation, it likewise re-acquires its solubility to any extent in water.

It is insoluble in alcohol and ether, and hence it is precipitated by strong alcohol added to its aqueous solution, the precipitate, if the alcohol is added in small quantity, being soluble in water. When alcohol is added to a somewhat dilute solution of albumen, the liquid after a while forms a gelatinous mass, which is liquefied by heat. Coagulated albumen may be made to dissolve in alcohol by the addition of an alkali. Nearly all acids precipitate albumen from its solution, especially nitric acid. Strong nitric acid with heat dissolves coagulated albumen, forming a blue or violet solution. Tribasic phosphoric acid, acetic, tartaric, and most other organic acids, do not form precipitates in moderately concentrated solutions, but when added to highly concentrated solutions the liquid solidifies to a jelly, which becomes liquid like gelatine when heated. In solutions of albumen to which common salt has been added, the albumen is precipitable by phosphoric, acetic, and other acids, or the albumen may be precipitated from the same acid solutions by means of salt, the precipitation being facilitated by the action of heat.

Albumen is soluble in weak solutions of alkalies, but a strong solution of potash, added in considerable quantity to a solution of albumen, forms a gelatinous mass. Alkaline carbonates prevent its coagulation by heat.

It has the same atomic composition as the other albuminoids, and contains, according to the best authorities, 15°8 per cent. of nitrogen.

Cerealin.-A nitrogenous substance approximating closely in its properties to diastase. It is contained in ihe membrane immediately surrounding the seed, called epispermium. It has the property of converting starch into dextrin, sugar, and lactic acid. This power is strikingly exemplified by adding an infusion of bran to a thick decoction of starch, which is quickly transformed as described above, the decoction becoming thin, limpid, and sweet, when kept at a temperature of from 40° to 50° C.

To obtain cerealin in a separate state, bran is treated with repeated quantities of dilute alcohol, it being pressed after each addition of the spirit. In this manner the whole of the sugar and dextrin are removed, the cerealin being left behind. The bran is next treated with water; this dissolves out the cerealin, and the aqueous solution being evaporated at 40° C., the cerealin is obtained in a pure state, it being soluble in water, but insoluble in alcohol and ether.

A solution containing cerealin coagulates at 75° C., and is precipitated on the addition of alcohol and by dilute acids. Alkalies prevent its action on starch. Once coagulated, it is no longer soluble in acids and alkalies, but it is still capable of slowly acting upon starch. Up to a temperature of 70° C. it retains its power of transforming starch, but not beyond that temperature, whereas diastase retains its power up to 90° C.

It would appear from the investigation of Mouriès that bran contains other substances besides cerealin which possess the power of converting starch, for he states that bran freed from cerealin, especially the perispermium, is more active than cerealin itself, and possesses the power of decomposing starch even at 100° C.

Starch. The only other constituent of flour which it will be necessary to notice is the starch, which forms nearly two-thirds of its weight. It belongs to the class of carbohydrates, which includes sugar, into which during digestion it is converted, the sugar being conveyed by absorption into the circulation, and broken up during respiration into carbonic acid and water, heat being developed during the

process.

The following analyses exhibit the precise percentage composition of different descriptions of wheat and wheat flour :