Flour and Bread
The adulterations to which flour and bread are exposed usually consist in adding damaged or an inferior grade of flour to wheaten flour, or in disguising the presence of a poor quality of flour by the addition of mineral substances, such as: plaster, chalk, lime, alum, and sulphate of copper.
Good flour has a white color, possessing a slightly yellow tinge, but is entirely free from red, grey or black specks. It is soft to the touch and adheres to the fingers, acquiring, when compressed in the hand, a soft cushion-like form. If mixed with water, it forms an elastic, homogeneous, but slightly coherent dough, which can be extended out in thin layers.
Flour of an inferior quality possess a dull white color, and does not assume the cushion-like condition mentioned above, when pressed in the hand, but escapes between the fingers: the dough formed is of a poorer quality.
Flour which has been damaged by moisture has a dull or reddish-white hue, and possesses a mouldy, or even a noxious, odor, as well as a bitter and nauseous taste which produces a marked acid sensation in the throat. Occasionally the presence of moisture causes the growth of fungi, the introduction of which in the digestive organs would cause serious results.
The constituents of pure flour are:
Gluten.
Starch, in the proportion of 50 to 75 per cent.
Dextrine, in the proportion of several per cent.
Glucose, in the proportion of several per cent.
Salts, remaining in the ash obtained by the calcination of the flour, in a proportion not exceeding 2 per cent.
Water, of which it loses 12 to 15 per cent., at the heat of a water-bath, and 15 to 20 per cent., at a temperature of 160°.
Bran, (ligneous and fatty matter,) in a very small proportion, when the flour has been properly bolted.
In the process of bread-making, the gluten undergoes fermentation by the action of the leaven and liberates carbonic acid, which causes the dough to become porous and swell up, or, as it is termed, to rise. Bread contains the same substances as flour, but gluten and starch are present in a state that does not admit of their separation by mechanical means, and glucose, if present at all, exists in a smaller quantity: the proportion of dextrine and water is, on the other hand, considerably increased. The bread of the Paris city bakeries contains 40 per cent. of water—the crumb, which forms 5/6 of the weight of the bread, containing 45 per cent.; the crust, which constitutes the remaining 1/6, containing 15 per cent. In army bread 43 per cent. of water are contained—the crumb, which constitutes 4/5 of the weight of the bread, holding 50 per cent.; the crust which forms the remaining 1/5, containing 15 per cent.
The addition of common salt naturally increases the proportion of ash left upon calcining bread.
Water is contained in stale bread in the same quantity as in fresh bread; but exists in a modified molecular condition: upon heating stale bread, it acquires the properties of fresh bread.
The following substances are used in the adulteration of wheaten flour:P
Potato-starch.
Meals of various grains (rice, barley, corn, oats and rye).
Vegetable meals, (beans, horse-beans, kidney-beans, peas, vetch, lentils, etc.).
Darnel meal.
Buckwheat flour.
Linseed-meal.
Mineral substances (plaster, chalk, lime, alum, and sulphate of copper).
In order to detect these substances, the gluten, the starch, and the ash are separately examined.
A. Examination of the Gluten
In order to separate the gluten, two parts of the flour to be examined and one part of water are mixed into a paste, and this is placed in a fine linen sack, in which it is kneaded under a stream of water so long as the washings have a turbid appearance: these are preserved. The gluten obtained from good wheaten flour possesses a light-yellow color; emits a stale odor; and spreads out, when placed in a saucer. In case the flour has been too strongly heated in the grinding, or otherwise badly prepared, the gluten is granulous, difficult to collect in the hand, and somewhat resembles flint-stone in appearance.
Gluten prepared from a mixture of equal parts of wheat and rye is adhesive, blackish, without homogeneousness, spreads out more readily than pure wheaten gluten, separates easily and adheres somewhat to the fingers.
Gluten obtained from a mixture of wheat and barley is non-adhesive, of a dirty reddish-brown color, and appears to be formed of intertwined vermicular filaments.
Gluten formed from a mixture of equal parts of wheat and oats has a blackish-yellow color and exhibits, at the surface, numerous small white specks.
The gluten from a mixture of wheat and corn has a yellowish color, is non-adhesive, but firm, and does not readily spread.
Gluten prepared from a mixture of wheat and leguminous flour is neither cohesive nor elastic, and, if the proportion of the latter present be considerable, can be separated and passed through a sieve, like starch.
The gluten obtained from a mixture of equal parts of wheat and buckwheat flour is very homogeneous, and is as easily prepared as the gluten from pure wheaten flour. It possesses when moist a dark-grey color; which changes to a deep black upon drying. The proportion of gluten in flour is exceedingly variable: good flour contains from 10 to 11 per cent. of dry gluten; poor flour from 8 to 9 per cent. of moist gluten, equal to about one-third of its weight of the dry compound.
B. Examination of the Starch
The washings of the flour are allowed to stand for some time in a conical-shaped vessel. As soon as the amylaceous matter has entirely settled to the bottom of the vessel, the greater portion of the water is decanted, and the residual mass brought upon a small filter and allowed to dry. The residue is then examined for potato and rice starch.
Potato starch. The grains of potato starch are much larger than those of wheaten starch. If a portion of the residue mentioned above is crushed in an agate mortar, the granules of potato starch present are ruptured, and their contents liberated; the wheaten starch remaining unaltered. The mass is then taken up with water, and the fluid filtered. If potato starch be present, the filtrate will acquire a blue color upon addition of an aqueous solution of iodine; otherwise, a yellow or violet-rose coloration is produced. It is necessary to avoid crushing the residue for too long a time, as the granules of wheaten starch would also become ruptured by prolonged comminution.
Besides the difference presented by potato starch in the size of the granules in comparison to those of wheaten starch, the former swell to ten or fifteen times the volume of the latter, when treated with a solution of potassa: wheaten starch granules are not affected by the treatment, if the solution used does not contain more than 2 per cent. of the salt. The results obtained by the above operation should be confirmed by a microscopic examination.
A portion of the residue is moistened with solution of iodine, then carefully dried, and placed on the slide of a microscope. The mass is next moistened with a solution containing 2 per cent. of potassa, and examined. The addition of iodine causes the potato starch granules to acquire a blue color, and renders their shape and volume more easily perceptible; thus allowing the two varieties of starch to be readily distinguished. Fig. 13 represents the relative size of the granules as observed under the microscope.Q
The presence of potato starch in bread is also detected by crushing a small portion of the sample under examination on the glass, and then adding a few drops of the alkaline solution.
Rice and Corn.—If rice or corn meal have been mixed with the flour, angular and translucent fragments (Fig. 14) are observed in the microscopic examination. Corn meal acquires a yellow color, if treated with dilute potassa solution.
Miscellaneous Tests
Linseed and rye meals.—If linseed meal is moistened with an aqueous solution containing 14 per cent. of potassa and examined under the microscope, numerous minute characteristic granules, smaller than the grains of potato-starch, are observed. These possess a vitreous appearance, sometimes a reddish color, and usually form in squares or very regular rectangles. The test is equally applicable to bread. The detection of linseed and rye meals is simultaneously effected by exhausting the suspected flour with ether, then filtering the solution and allowing it to evaporate. If the flour contains rye, the oil left by the evaporation, when heated with a solution of mercury in concentrated nitric acid, is converted into a solid substance having a fine red color; but it remains unaltered, if entirely due to linseed. In case the oil becomes solidified, the mercury salt present should be removed by washing with water, the residue taken up with boiling alcohol of 36° B. and the solution filtered: upon evaporating the alcoholic filtrate, a residue is obtained consisting of the linseed oil present.
Buckwheat.—Flour adulterated with buckwheat is less soft to the touch, does not pack as easily, and passes more readily through a sieve than pure wheaten flour. It presents, here and there, blackish particles, due to the perisperm of the grain, and has a dirty-white color. As previously remarked, the gluten obtained from a mixture of buckwheat and wheaten flour possesses a grey or even a black color. The starch furnished by buckwheat flour exhibits polyhedral agglomerations, analogous to those presented by corn.
Darnel.—The use of darnel in the adulteration of wheaten flour may give rise to serious sanitary results. To effect its detection, the flour to be examined is digested with alcohol of 35° B.: if the flour be pure, the alcohol remains limpid: it acquires a straw-yellow tint, due to traces of bran present, but—although a peculiar resin may be dissolved—the solution does not possess a disagreeable taste. When, on the contrary, darnel is present, the alcohol assumes a green tint, which gradually deepens, and possesses a bitter and nauseous taste; the residue, left by the evaporation of the tincture to dryness, has a greenish-yellow color, and a still more disagreeable flavor than the alcoholic solution.
Legumens.—Leguminous meals cannot be added otherwise than in small proportions to wheaten flour, owing to the rapidity with which they change the properties of the latter, and communicate to it their characteristic odor—noticeable upon treating the flour with a little boiling water. Their presence is also easily detected by the distinctive properties of the vegetable itself, and by the appearance of the amylaceous residue in the microscopic examination. In order to decide as to the presence of legumens, the washings containing the starchy matter of the flour, after the particles of gluten present have been separated by passing the fluid through a silk sieve, are divided into two portions. One portion is allowed to undergo fermentation, at a temperature of 18° to 20°: in case leguminous substances are not present, lactic fermentation occurs and the odor of sour milk is alone perceptible; if, on the other hand, legumens are contained in the fluid, rancid fermentation takes place, and an odor is emitted resembling that of decayed cheese. The remaining portion of the washings, after being decanted from the residue of amylaceous matter, is filtered and evaporated until a yellowish translucent pellicle appears upon its surface. The fluid is then again filtered from the coagulated albumen common to all flours, and the leguminous substances present coagulated by the addition, drop by drop, of acetic acid.
The leguminous deposit produced appears white and flaky; when examined under the microscope, it presents lamilla emarginated at the border; it is odorless and tasteless; when dried, it assumes a horny appearance; it is insoluble, both in water and alcohol, and does not become gelatinous when treated with boiling water; it is readily soluble in potassa and other alkaline solutions, from which it is precipitated upon addition of nitric, hydrochloric, acetic, oxalic, and citric acids; upon protracted boiling in water, it loses its property of being soluble in ammonia. The above tests having been applied, the residue containing the starch is next examined. For this purpose, a small portion is moistened with a little water, a few drops of iodine solution added, and the mixture placed on the side of the microscope: the bluish grains contained in the polyhedral and cellular envelope (Fig. 15) are easily recognized. The mixture on the glass may also be treated with an aqueous solution of potassa (containing 10 per cent. of the salt), or with dilute hydrochloric acid: these reagents dissolve the starch present, leaving the reticulated tissue intact. Should this examination fail to give a definite result, the remaining portion of the amylaceous residue is subjected to a sort of levigation, and the part most slowly deposited separated. In this portion the reticulated tissues of the leguminous substances present are contained, and, as they are comparatively free from foreign matters, their identification is a matter of comparative ease. In case the presence of reticulated tissue is indicated, it is still necessary to apply confirmatory chemical tests.
Meals prepared from beans, horse-beans, and lentils, contain a tannin which imparts a green or black color to salts of iron. The coloration is rendered very sensitive if a rather considerable quantity of the flour to be examined is passed through a silk sieve, and the remaining bran treated with a solution of sulphate of iron (ferrico-ferrous sulphate): the reaction immediately occurs, even if the sample contains but 10 per cent. of bean meal. The meals of horse-beans and of vetches acquire a red color, when exposed to the successive action of nitric acid and of ammonia vapors. In order to apply this test, the suspected flour is placed upon the edge of a capsule containing nitric acid, the latter heated, and, as a yellow coloration appears, the acid removed and replaced by ammonia. The capsule is then set aside: if the flour is adulterated with either of the above vegetables, reddish spots, which are easily perceptible by aid of a magnifying glass, are soon produced.
In case bread is to be examined, it is exhausted with water, the fluid passed through a sieve, the upper layer decanted, then evaporated, and the residue taken up with alcohol. The tincture so obtained is evaporated, and the second residuum treated with nitric acid and ammonia, as directed above. When meals prepared from beans, vetches, or lentils are heated on a water-bath with hydrochloric acid, diluted with three to four times its volume of water, a cellular tissue, possessing the color of wine-dregs, remains behind; flours of wheat, peas, and kidney-beans leave a colorless residue, when subjected to the same treatment.
Finally; the grains of the starch (fecula) of legumens possess a volume about equal to that of potato granules, and exhibit either a longitudinal furrow in the direction of their longer axis, or a double furrow arranged in a star-like form.
c. Examination of the Ash
Leguminous substances, and more particularly mineral salts, are detected by the examination of the ash left upon the incineration of the flour.
Detection of Legumens.—Pure wheaten flour furnishes an ash consisting of about 2 per cent. of its weight; whereas meals of legumens leave from 3 to 4 per cent. of their weight in ash. This difference is, however, too slight to furnish conclusive results; the analysis of the ash is also necessary. The ash of wheaten flour is non-deliquescent, dry, semi-fused, and chiefly consists of phosphates of potassa, soda, magnesia and lime, of sulphates, and of silica. The solution obtained by treating the ash with water has an alkaline reaction. The phosphates of the alkalies, present in the ash of wheat, exist in the state of pyrophosphates, and, as chlorides are absent, the addition of nitrate of silver to the aqueous solution of the ash produces a white precipitate, consisting entirely of pyrophosphate of silver, which is not affected by exposure to the light.
The ash of leguminous meals is deliquescent and soluble in water, forming a strongly alkaline solution, which contains both chlorides and neutral phosphates. The latter give a clear yellow precipitate with nitrate of silver. Upon adding a solution of this salt to the aqueous solution of the ash, a pale yellow precipitate, which turns violet if exposed to the light, is therefore produced.
Detection of mineral substances.—The principal mineral substances, that are fraudulently added to flour, are ground calcined bones, sand, lime, plaster, alum, and sulphate of copper. The two last named salts are almost invariably added in small quantities; alum renders the flour white, even when used in the proportion of one per cent.; sulphate of copper is added to impart a good appearance to bread made from a damaged flour.
a. Ground bones (carbonate and phosphate of lime).—The washings of the gluten are placed in a conical vessel, and, after some time has elapsed, the clear supernatant fluid is removed by means of a syphon, a conical shaped deposit remaining on the bottom of the vessel: two hours later, the fresh layer of fluid that has formed is removed with a pipette. As soon as the residue becomes nearly solid, it is detached from the vessel, placed upon a fragment of plaster, and allowed to dry. The bones, being heavier than the amylaceous substances, are to be found in the apex of the cone formed by the residue. This is detached, and incinerated: in case the ash obtained contains phosphate and carbonate of lime, the addition of hydrochloric acid will cause effervescence, and, upon adding ammonia to the acid solution, a white precipitate will be formed. If the solution is then filtered and oxalate of ammonia added to the filtrate, a precipitate will be produced which, when heated to redness, leaves a residue of caustic lime possessing an alkaline reaction.
b. Sand.—As this substance possesses a much greater specific gravity than the usual constituents of flour, it is only necessary, in order to accomplish its separation, to repeatedly stir the flour with water, and remove the deposit at first formed, which, if consisting of sand, will be insoluble in acids, and will grate, when placed between the teeth.
c. Carbonates of lime and magnesia; vegetable ashes.—Carbonic acid is always evolved, upon treating flour with hydrochloric acid. If the base present be calcium, upon adding oxalate of ammonia to the filtered solution—which has previously been neutralized with ammonia—a white precipitate, possessing the properties mentioned above, will be formed; in case the base is magnesia, the addition of oxalate of ammonia will fail to cause a precipitate, but upon adding solution of phosphate of ammonia to the fluid a granular precipitate of phosphate of ammonia and magnesia is produced; if, finally, the flour contains vegetable ashes—i. e. carbonates of the alkalies—bichloride of platinum will produce in the acid solution a yellow precipitate: the addition of vegetable ashes, moreover, would render the ash of the flour deliquescent and very strongly alkaline.
d. Lime.—In presence of lime, carbonic acid produces a white precipitate, when conducted into the filtered aqueous extract of the flour.
e. Plaster.—The flour is boiled with water acidulated with hydrochloric acid, the fluid filtered, and lime detected in the filtrate by means of ammonia and oxalate of ammonia. The presence of sulphuric acid is indicated by the formation of a precipitate insoluble in acids, upon addition of solution of chloride of barium. Upon calcining the flour without access of air, sulphate of lime is converted into the corresponding sulphide: the residue of the calcination, when treated with hydrochloric acid, evolves sulphuretted hydrogen, and the lime present in the filtered acid solution is likewise precipitated by the addition of ammonia and oxalate of ammonia.
f. Alum.—A portion of the flour to be examined is treated with water, the fluid filtered, and the filtrate divided in two portions: in one, sulphuric acid is detected by means of chloride of barium; in the other, alumina by adding a solution of potassa, which gives with its salts a white gelatinous precipitate, soluble in an excess of the reagent.R
g. Sulphate of copper.—About 200 grammes of the bread under examination are incinerated; the ash treated with nitric acid; the mixture evaporated until it acquires a sticky consistence, and the mass then taken up with water. The aqueous solution is next filtered; an excess of ammonia and several drops of solution of carbonate of ammonia added; the fluid again filtered, the filtrate slightly acidulated with nitric acid, and divided into two parts. It is then ascertained if sulphuretted hydrogen produces in one portion of the solution a brown precipitate of sulphide of copper, and if solution of ferrocyanide of potassium produces in the other a reddish-brown precipitate of ferrocyanide of copper.S