Popular Science Monthly/Volume 24/April 1884/The Chemistry of Cookery XI
|THE CHEMISTRY OF COOKERY.|
THERE is one more constituent of animal food that demands attention before leaving this part of the subject. This is the fat. We all know that there is a considerable difference between raw fat and cooked fat; but what is the rationale of this difference? Is it anything beyond the obvious fusion or semi-fusion of the solid?
These are very natural and simple questions, but in no work on chemistry or technology can I find any answer to them, or even any attempt at an answer. I will therefore do the best I can toward solving the problem in my own way.
All the cookable and eatable fats fall into the class of "fixed oils," so named by chemists to distinguish them from the "volatile oils," otherwise described as "essential oils." The distinction between these two classes is simple enough. The volatile oils (mostly of vegetable origin) may be distilled or simply evaporated away like water or alcohol, and leave no residue. The fixed oils similarly treated are dissociated more or less completely.
Otherwise expressed, the boiling-point of the volatile oils is below their dissociation-point. The fixed oils are those which are dissociated at a temperature below their boiling-point.
My object in thus expressing this difference will be understood upon a little reflection. These volatile oils, when heated, being distilled without change are uncookable; while the fixed oils if similarly heated suffer various degrees of change as their temperature is raised, and may be completely decomposed by steady application of heat in a closed vessel without the aid of any other chemical agent than the heat itself. This "destructive distillation" converts them into solid carbon and hydrocarbon gases, similar to those we obtain by the destructive distillation of coal.
If we watch the changes occurring as the heat advances to this complete dissociation-point, we may observe a gradation of minor or partial dissociation proceeding gradually onward, resembling that which I have already described as occurring when sugar is similarly treated (see No. XIII of this series).
But in ordinary cooking we do not go so far as to carbonize the fat itself, though we do brown or partially carbonize the membrane which envelops the fat. What, then, is the nature of this minor dissociation, if such occurs?
Before giving my answer to this question, I must explain the chemical constitution of fat. It is a compound of a very weak base with very weak acids. The basic substance is glycerine, the acids (not sour at all, but so named because they combine with bases as the actually sour acids do) are stearic acid, palmitic acid, oleic acid, etc., and bear the general name of fatty acids. They are solid or liquid, according to temperature. When solid, they are pearly, crystalline substances ; when fused, they are oily liquids.
To simplify, I will take one of these as a type, and that the one which is the chief constituent of animal fats, viz., stearic acid. I have a lump of it before me. Newly broken through, it might at a distance be mistaken for a piece of Carrara marble. It is granular like the marble, but not so hard, and, when rubbed with the hand, differs from the marble in betraying its origin by a small degree of unctuousness, but can scarcely be described as greasy.
I find by experiment that this may be mixed with glycerine without combination taking place; that when heated with glycerine just to its fusing-point, and the two are agitated together, the combination is by no means complete. Instead of obtaining a soft, smooth fat, I obtain a granular fat, small stearic crystals with glycerine among them. It is a mixture of stearic acid and glycerine, not a chemical compound; it is stearic acid and glycerine, but not a stearate of glycerine.
A similar separation is what I suppose to occur in the cooking of animal fat. I find that mutton-fat, beef-fat, or other fat when raw, is perfectly smooth, as tested by rubbing a small quantity, free from membrane, between the finger and thumb, or by a still more delicate test of rubbing it between the tip of the tongue and the palate. But dripping, whether of beef, or mutton, or poultry, is granular, as anybody who has ever eaten bread and dripping knows well enough, and the manufacturers of "butterine," or "bosch," know too well, as the destruction or prevention of this granulation is one of the difficulties of their art.
My theory of the cookery of fat is simply that heat, when continued long enough, or raised sufficiently high, effects an incipient dissociation of the fatty acids from the glycerine, and thus assists the digestive organs by presenting the base and the acids in a condition better fitted (or advanced by one stage) for the new combinations demanded by assimilation. Some physiologists have lately asserted that the fat of our food is not assimilated at all not laid down again as fat, but is used directly as fuel for the maintenance of animal heat. If this is correct, the advantage of the preliminary dissociation is more decided, for the combustible portion of the fat is its fatty acids; the glycerine is an impediment to combustion, so much so that the modern candle-maker removes it, and thereby greatly improves the combustibility of his candles.
It may be that the glycerine of the fat we eat is assimilated like sugar, while the fatty acids act directly as fuel. This view may reconcile some of the conflicting facts (such as the existence of fat in the carnivora) that stand in the way of the theory of the uses of fat food above referred to, according to which fat is not fattening, and those who would "Bant" should eat fat freely to maintain animal heat, while very abstemious in the consumption of sugar and farinaceous food.
The difference between tallow and dripping is instructive. Their origin is the same; both are melted fats—beef or mutton fats—and both contain the same fatty acids and glycerine, but there is a visible and tangible difference in their molecular condition. Tallow is smooth and homogeneous, dripping decidedly granular.
I attribute this difference to the fact that, in rendering tallow, the heat is maintained no longer than is necessary to effect the fusion; while, in the ordinary production of dripping, the fat is exposed in the dripping-pan to a long continuance of heat, besides being highly heated when used in basting. Therefore the dissociation is carried further in the case of the dripping, and the result becomes sensible. I have observed that home-rendered lard, that obtained in English farm-houses, where the "scratchings" (i.e., the membranous parts) are frizzled, is more granular than the lard we now obtain in such abundance from Chicago and other wholesale hog-regions. I have not witnessed the lard-rendering at Chicago, but have little doubt that economy of fuel is practiced in conducting it, and therefore less dissociation would be effected than in the domestic retail process.
Some of the early manufacturers of "bosch" purified their fat by the process recommended and practiced by the French Academicians MM. Dubrunfaut and Fua (see "Comptes Rendus," vol. lxxi) during the siege of Paris, when they and others read papers on the manufacture of "siege-butter" without the aid of the dairy. This consisted in frying the refuse fat from slaughter-houses until the membranous matter and other impurities were carbonized, and thus could be strained away. I wrote about it in 1871, and consequently received some samples of artificial butter thus made in the midlands. It was pure fat, perfectly wholesome, but, although colored to imitate butter, had the granular character of dripping. Since that time great progress has been made in this branch of industry. I have lately tasted samples of pure "bosch" or "oleomargarine" undistinguishable from churned cream or good butter, though offered for sale at 82d. per pound in wholesale packages. In the preparation of this I understand high temperatures are carefully avoided, and by this means the smoothness of pure butter is obtained. I mention this now merely in confirmation of my theory of the rationale of fat-cookery, but shall return to this subject of "bosch" or "butterine" again, as it has considerable intrinsic interest in reference to our food-supplies, and should be better understood than it is.
The cookery of milk is very simple, but by no means unimportant. That there is an appreciable difference between raw and boiled milk may be proved by taking equal quantities of each (the boiled sample having been allowed to cool down), adding them to equal quantities of the same infusion of coffee, then critically tasting the mixtures. The difference is sufficient to have long since established the practice among all skillful cooks of scrupulously using boiled milk for making café au lait. I have tried a similar experiment on tea, and find that in this case the cold milk is preferable. Why this should be, why boiled milk should be better for coffee and raw milk for tea, I can not tell. If any of my readers have not done so already, let them try similar experiments with condensed milk, and I have no doubt that the verdict of the majority will be that it is passable with coffee, but very objectionable in tea. This is milk that has been very much cooked.
The chief definable alteration effected by the boiling of milk is the coagulation of the small quantity of albumen which it contains. This rises as it becomes solidified, and forms a skin-like scum on the surface, which may be lifted with a spoon and eaten, as it is perfectly wholesome and very nutritious.
If all the milk that is poured into London every morning were to flow down a single channel, it would form a respectable little rivulet. An interesting example of the self-adjusting operation of demand and supply is presented by the fact that, without any special legislation or any dictating official, the quantity required should thus flow with so little excess that, in spite of its perishable qualities, little or none is spoiled by souring, and yet at any moment anybody may buy a pennyworth within two or three hundred yards of any part of the great metropolis. There is no record of any single day on which the supply has failed, or even been sensibly deficient.
This is effected by drawing the supplies from a great number of independent sources, which are not likely to be simultaneously disturbed in the same direction. Coupled with this advantage is a serious danger. It has been unmistakably demonstrated that certain microbia (minute living abominations) which disseminate malignant diseases may live in milk, feed upon it, increase and multiply therein, and by it be transmitted to human beings with very serious and even fatal results.
I speak the more feelingly on this subject, having very recently had painful experience of it. One of my sons went for a holiday to a farm-house in Shropshire, where many happy and health-giving holidays have been spent by all the members of my family. At the end of two or three weeks he was attacked by scarlet fever, and suffered severely. He afterward learned that the cow-boy had been ill, and further inquiry proved that his illness was scarlet fever, though not acknowledged to be such; that he had milked before the scaling of the skin that follows the eruption could have been completed, and it was therefore, most probable, that some of the scales from his hands fell into the milk. My son drank freely of uncooked milk, the other inmates of the farm drinking home-brewed beer, and only taking milk in tea or coffee hot enough to destroy the vitality of fever-germs. He alone suffered. This infection was the more remarkable, inasmuch as a few months previously he had been assisting a medical man in a crowded part of London where scarlet fever was prevalent, and had come in frequent contact with patients in different stages of the disease.
Had the milk from this farm been sent to London in the usual manner in cans, and the contents of these particular cans mixed with those of the rest received by the vender, the whole of his stock would have been infected. As some thousands of farms contribute to the supplying of London with milk, the risk of such contact with infected hands occurring occasionally in one or another of them is very great, and fully justifies me in urgently recommending the manager of every household to strictly enforce the boiling of every drop of milk that enters the house. At the temperature of 212° the vitality of all dangerous germs is destroyed, and the boiling-point of milk is a little above 212°. The temperature of tea or coffee, as ordinarily used, may do it, but is not to be relied upon. I need only to refer generally to the cases of wholesale infection that have recently been traced to the milk of particular dairies, as the particulars are familiar to all who read the newspapers.
It is an open question whether butter may or may not act as a dangerous carrier of such germs; whether they rise with the cream, survive the churning, and nourish among the fat. The subject is of vital importance, and yet, in spite of the research-fund of the Royal Society, the British Association, etc., we have no data upon which to base even an approximately sound conclusion.
We may theorize, of course; we may suppose that the bacteria, bacilli, etc., which we see under the microscope to be continually wriggling about or driving along, are doing so in order to obtain fresh food from the surrounding liquid, and therefore that, if imprisoned in butter, they would languish and die. We may point to the analogies of ferment-germs which demand nitrogenous matter, and therefore suppose that the pestiferous wanderers can not live upon a mere hydrocarbon like butter. On the other hand, we know that the germs of such things can remain dormant under conditions that are fatal to their parents, and develop forthwith when released and brought into new surroundings. These speculations are interesting enough, but in such a matter of life and death to ourselves and our children we require positive facts, direct microscopic evidence.
In the mean time the doubt is highly favorable to boseh. To illustrate this, let us suppose the case of a cow grazing on a sewage-farm manured from a district on which enteric fever has existed. The cow lies down and its teats are soiled with liquid containing the germs which are so fearfully malignant when taken internally. In the course of milking, a thousandth part of a grain of the infected matter containing a few hundred germs enters the milk, and these germs increase and multiply. The cream that rises carries some of them with it, and they are thus in the butter, either dead or alive, we know not which, but have to accept the risk.
Now, take the case of bosch. The cow is slaughtered. The waste fat, that before the days of palm-oil and vaseline was sold for lubricating machinery, is skillfully prepared, made up into two-pound rolls, delicately wrapped in special muslin or prettily molded and fitted into "Normandy" baskets. What is the risk in eating this?
None at all, provided always the bosch is not adulterated with cream-butter. The special disease-germs do not survive the chemistry of digestion, do not pass through the glandular tissues of the follicles that secrete the living fat, and therefore, even though the cow should have fed on sewage-grass, moistened with infected sewage-water, its fat would not be poisoned.
What we require in connection with this is commercial honesty, that the thousands of tons of bosch now annually made be sold as bosch, or, if preferred, as "oleomargarine," or "butterine," or any other name that shall tell the truth. In order to render such commercial honesty possible to shopkeepers, more intelligence is demanded among their customers. A dealer, on whom I can rely, told me lately that if he offered the bosch or butterine to his other customers as he was then offering it to me at 82d. per pound in twenty-four-pound box, or 9d. retail, he could not possibly sell it, and his reputation would be injured by admitting that he kept it; but that the same people who would be disgusted with it at 9d. will buy it freely at double the price as prime Devonshire fresh butter; and he added, significantly, "I can not afford to lose my business and be ruined because my customers are fools." To pastry-cooks and others in business, it is sold honestly enough for what it is, and used instead of butter.
Before leaving the subject of animal food I may say a few words on the latest and perhaps the greatest triumph of science in reference to food-supply—i.e., the successful solution of the great problem of preserving fresh meat for an almost indefinite length of time. It has long been known that meat which is frozen remains fresh. The Aberdeen whalers were in the habit of feasting their friends on returning home on joints that were taken out fresh from Aberdeen and kept frozen during a long Arctic voyage. In Norway, game is shot at the end of autumn, and kept in a frozen state for consumption during the whole winter and far into the spring.
The early attempts to apply the freezing process for the carriage of fresh meat from South America and Australia by using ice, or freezing mixtures of ice and salt, failed, but now all the difficulties are overcome by a simple application of the great principle of the conservation of energy, whereby the burning of coal may be made to produce a degree of cold proportionate to the amount of heat it gives out in burning.
Carcasses of sheep are thereby frozen to stony hardness immediately they are slaughtered in New Zealand and Australia, and then packed in close refrigerated cars, carried to the ship, and there stowed in chambers refrigerated by the same means, and thus brought to England in the same state of stony hardness as that originally produced. I dined to-day on one of the legs of a sheep that I bought a week ago and which was grazing at the antipodes three months before. I prefer it to any English mutton ordinarily obtainable.
The grounds of this preference will be understood when I explain that English farmers who manufacture mutton as a primary product kill their sheep as soon as they are full grown, when a year old or less. They can not afford to feed a sheep for two years longer merely to improve its flavor without adding to its weight. Country gentlemen who do not care for expense occasionally regale their friends on a haunch or saddle of three-year-old mutton, as a rare and costly luxury.
The antipodean graziers are wool-growers. Until lately, mutton was merely used as manure, and even now it is but a secondary product. The wool-crop improves year by year until the sheep is three or four years old; therefore, it is not slaughtered until this age is attained, and thus the sheep sent to England are similar to those of the country squire, and such as the English farmer could not send to market under eighteen pence per pound.
There is, however, one drawback; but I have tested it thoroughly, having supplied my own table during the last six months with no other mutton than that from New Zealand, and find it so trifling as to be imperceptible unless critically looked for. It is simply that, in thawing, a small quantity of the juice of the meat oozes out. This is more than compensated by the superior richness and fullness of flavor of the meat itself, which is much darker in color than young mutton.—Knowledge.