On the Adulteration of Food, Principally with a View to its Detection by the Microscope.
(Abstract of a Paper read before the Manchester Literary and Philosophical Society.)
By WALTER MORRIS.
Adulteration was defined as being the fraudulent addition to any substance of another, for the sake of increased sale or profit. There are several modes of accomplishing this end; the first, and the most common, is by addition of some article to increase the bulk or weight, as when starch is added to mustard, and cheaper flours to wheaten flour; the second by improving the appearance and apparent quality, so as to sell an inferior article at the price of a better, as in the case of the artificial coloring of pickles made of stale vegetables to resemble fresh. One of the commonest apologies for these practices is that the public prefer the adulterated article to the pure; that, for instance, pure mustard "will not sell." This allegation is, however, hardly a fair one, as the pure article is never offered; and, doubtless, if the pure article were used as freely as the ordinary mixture, it would be found unexpectedly pungent. But the fallacy of such apologies has been exposed by the example of pickles, which under this plea used to be invariably colored with an artificial and frequently poisonous pigment. The public eye was thus educated to expect them of a bright green; yet, since some manufacturers have exposed the fraud and sent out pure pickles, the public have completely turned round, and avoid any which show an unnatural color.
The adulteration of bread and flour with alum, to make them look whiter and of a superior quality, has to some extent diminished; but that substance is often replaced by the still worse sulphate of copper, or blue vitriol, which was recently detected in sixteen out of twenty loaves tested. In this case the public has been led to suppose that the quality of bread is shown by its whiteness, whereas by taking out the bran a most valuable part of the grain, viz., its azotised or flesh-forming portion, is lost. Less dangerous admixtures are those of cheaper flours, such as barley, rice, and "cones" (the latter made from a species of wheat called revet), and even beans.
The adulteration of coffee with chicory, though so well understood, exists, especially in poorer neighborhoods, to an extent hardly credible. Out of forty-seven samples, eigtheen were found pure, the lowest price of which was 1s. 4d. per lb.; of the rest, most were half, and some where wholly composed of chicory, which, being worth about 6d. per lb., was thus sold at 1s. and 1s. 4d. The difference can be readily detected by the microscope, the cells of chicory being much larger, and the cell walls much thinner than those of coffee.
Even chicory itself is much adulterated; out of fifty-seven samples only about one-half were pure, the adulterants being roasted wheat, acorns, beans, carrots and sawdust.
Tea is less subject to adulteration than many articles of food; such abominations as the celebrated Maloo mixture, consisting of old used leaves re-dried, willow leaves and twigs, and even iron filings, have been quickly detected and refused by the trade. The "facing," however, of green tea with poisonous coloring matter is both absurd and harmful: and it will probably be continued so long as the public are content to accept such a palpable imposture as "genuine green."
It is a matter of opinion whether cocoa as ordinarily sold is to be considered an adulterated or a manufactured article. It is seldom sold pure and alone; being usually mixed with starch and sugar—the term "pure cocoa" is therefore, in most cases, intended to mislead. Some kinds have lard or suet admixed, and to others red ochre is added to bring up the color, rendered pale by an excessive quantity of starch. The relative quantities of these component parts in any sample of cocoa may be readily ascertained by the microscope; that of starch may be roughly seen by shaking up some of the cocoa with water in a test-tube or tall bottle, breaking up the lumps, and then allowing all to settle; when the starch will sink to the bottom and form a white layer beneath the cocoa. On warming the water, the fat will of course float to the top, and the sugar will be dissolved. The sugar crystals and fat are also shown by re-drying the solution on a glass slide.
Sugar is mixed with inferior kinds of the same article, but not (as popularly believed) with sand; the chief impurities in raw sugar are cane fibre, accidental dirt, and the sugar mite or acarus. The latter exists in most raw sugars (out of 72 samples 69 contained mites); but more abundantly in the moderately brown kinds than in the darker. The insect is barely visible to the naked eye. To obtain specimens, the sample should be dissolved in tepid water and well stirred, then allowed to stand a few minutes, and the acari will be found as minute particles floating on the top. The process of refining entirely removes these and the other impurities named.
Mustard is invariably adulterated with flour, which forms one-half or three-fourths of the article usually sold. It may be readily detected by the microscope, mustard itself containing no starch whatsoever. Turmeric is often added to bring up the color after this whole-sale admixture, and cayenne to give it strength.
Pepper may now be obtained pure of respectable dealers; but as regards the cheaper kinds, and in poor neighborhoods, it is largely adulterated with meal or starch, gypsum, and dirt of any kind, to give bulk and weight. The starchy substance may be detected by the microscope, the earthy ones will be left as ash after burning, and their character may be ascertained by the polariscope. The particles of pepper itself are easily recognized by the characteristic stellate cells in the outer skin, and the hard angular ones of the inner part of the seed.
Many examples of the above and other kinds of adulteration, mounted for the microscope, were exhibited at the same time, for comparison with pure specimens.—Lond. Chem. News, October 27, 1871.