Popular Science Monthly/Volume 23/August 1883/The Chemistry of Cookery III
|THE CHEMISTRY OF COOKERY.|
A SHEEP or an ox, a fowl or a rabbit, is made up, like ourselves, of organic structures and blood, the organs continually wasting as they work, and being renewed by the blood; or, otherwise described, the component molecules of these organs are continually dying of old age as their work is done, and replaced by new-born successors generated by the blood.
These molecules are, for the most part, cellular, each cell living a little life of its own, generated with a definite individuality, doing its own life-work, then shriveling in decay, dying in the midst of vital surroundings, suffering cremation, and thereby contributing to the animal heat necessary for the life of its successors, and even giving up a portion of its substance to supply them with absorption-food. The cell-walls are mainly composed of gelatine, or the substance which produces gelatine, as already explained, while the contents of the cell are albuminous matter or fat, or the special constituents of the particular organ it composes. A description of all these constituents would carry me too far into details. I must, therefore, only refer to those which constitute the bulk of animal food, and which are altered in the process of cooking.
In the lean of meat, i. e., the muscles of the animal, we have the albuminous juices already described, the gelatinous membranes, sheaths, and walls of the muscular fiber, and the fiber itself. This is composed of muscular fibrin, or syntonin, as Lehmann has named it. Living blood consists of a complex liquid, in which are suspended a multitude of minute cells, some red, others colorless. When the blood is removed and dies, it clots or partially solidifies, and is found to contain a network of extremely fine fiber, to which the name of fibrin is applied. A similar change takes place in the substance of the muscle after death. It stiffens, and this stiffening, or rigor mortis, is effected by the formation of a clot analogous to the coagulation of the blood, and the substance of this clot (myosin) is so nearly like the fibrin of the blood and the material of the muscular fiber (syntonin) that for our purpose they may be all described as varieties of fibrin.
The properties of fibrin, so far as cookery is concerned, place it between albumen and gelatine; it is coagulable like albumen, and soluble like gelatine, but in a minor degree. Like gelatine, it is tasteless, and non-nutritious alone. This has been proved by feeding animals on lean meat, which has been cut up and subjected to the action of cold water, which dissolves out the albumen and other juices of the flesh, and leaves only the muscular fiber and its envelopes. The same is the case with the spontaneously coagulated fibrin of the blood; it is, when washed, a yellowish, opaque, fibrous mass, without smell or taste, insoluble in cold water, alcohol, or ether, but imperfectly soluble if digested for a considerable time in hot water.
The following is the chemical composition of these three constituents of lean meat, according to Müller:
|Sulphur||1·6||. . . .||1·2|
|Phosphorus||0·4||. . . .||0·3|
There are two other constituents of lean meat which are very different from either of these, viz., Kreatine and Kreatinine, otherwise spelled creatine and creatinine. These exist in the juice of the flesh, and are freely soluble in cold or hot water, from which solution they may be crystallized by evaporating the solvent, just as we may crystallize common salt, alum, etc. They thus have a resemblance to mineral substances, and still more so to some of the active constituents of plants, such as the alkaloids, theine, and caffeine, upon which depend the stimulating or "refreshing" properties of tea and coffee.
Their chemical composition and general relations have suggested the theory that they are the dead matter of muscle, the first and second products of the combustion which accompanies muscular work, urea being the final product. According to this, their relation to the muscle is exactly the opposite of that of the albuminous juice, this being probably the material from which the muscle is built up or renewed. The following is their composition, according to Liebig's analyses:
The juices of lean flesh also contain a little lactic acid—the acid of milk—but this does not appear to be an absolutely essential constituent. Besides these there are mineral salts of considerable nutritive importance, though small in quantity. These, with the kreatine and kreatinine, are the chief constituents of beef-tea, properly so called, and will be further treated when I come to that preparation. At present it is sufficient to keep in view the fact that these juices are essential to complete the nutritive value of animal food.
I may now venture to state my own view of a somewhat obscure subject, viz., the difference between the roasting or grilling and the stewing of meat. It appears to me that, with the exception of the superficial "browning," it consists simply in the difference between the cooking media; that a grilled steak or chop or a roasted joint is meat that has been stewed in its own juices instead of stewed in water; that in both cases the changes taking place in the solid parts of the meat are the same in kind, provided always that the roasting or grilling is properly performed. The albumen is coagulated in all cases, and the gelatinous and fibrous tissues are softened by being heated in a liquid solvent. I shall presently apply this definition in distinguishing between good and bad cookery.
In the roasted or grilled meat the juices are retained in the meat (with the exception of that which escapes as gravy on the dish), while in stewing the juices go more or less completely into the water, and the loosening of the fibers and solution of the gelatine and fibrin may be carried further, inasmuch as a larger quantity of solvent is used.
Roasting and grilling may be regarded as our national methods of flesh cookery, and stewing in water that of our Continental neighbors. The difference between the flavor of English roast beef and French bouilli or Italian manzo is due to the retention or the removal of the saline and highly flavored soluble materials. (Concentrated kreatine and kreatinine are pungently sapid.) The Frenchman takes them out of his bouilli, or boiled meat, and transfers them to his bouillon, or soup, which with him is an essential element of a meal. If he ate his meat without soup, he would be like the dogs fed on gelatine by the bone-soup commissioners. To the Englishman, with his roast or grilled meat, soup is merely a luxury, not a necessary element of complete dietary.
What we call boiled meat, as a boiled leg of mutton or round of beef, is an intermediate preparation. The heat is here communicated by water and the juices partially retained.
As this is of essential importance, I should perhaps have stated it with some emphasis. More than a pint of water should be used rather than less, as upon the quantity of water depends the retention of the heat. If the quantity of water is smaller, it should be kept boiling about half a minute before setting aside.
The application of the principles already expounded to the processes of grilling and roasting is simple enough. As the meat is to be stewed in its own juices, it is evident that these juices must be retained as completely as possible, and that in order to succeed in this we have to struggle with the evaporating energy of the "dry heat" which effects the cookery.
It should be clearly understood that the so-called "dry heat" may be communicated by convection or by radiation, or both. When water is the heating medium, there is convection only, i. e., heating by actual contact with the heated body. In roasting and grilling there is also some convection-heating due to the hot air which actually touches the meat; but this is a very small element of efficiency, the work being chiefly done, when well done, by the heat which is radiated from the fire directly to the surface of the meat, and which, in the case of roasting in front of a fire, passes through the intervening air with very little heating effect thereon.
I am not perpetrating any far-fetched pedantry in pointing out this difference, as will be understood at once by supposing that a beefsteak should be cooked by suspending it in a chamber filled with hot dry air. Such air is actively thirsting for the vapor of water, and will take into itself, from every humid substance it touches, a quantity proportionate to its temperature. The steak receiving its heat by convection, i. e., the heat conveyed by such hot air, and communicated by contact, would be desiccated, but not cooked.
This distinction is so important that I will illustrate it still further, my chief justification for such insistence being that even Rumford himself evidently failed to understand it, and it has been generally misunderstood or neglected.
Let us suppose the hot air used for convection cooking to be at the cooking-point, as the hot water in stewing should be, what will follow its application to the meat? Evaporation of the water in the juices, and with that evaporation a lowering of temperature at the surface of the meat, keeping it below the cooking-point. If the air be heated above this, the evaporation will go on with proportionate rapidity, and as nearly one thousand degrees of heat are lost as temperature, and converted into expansive force whenever and wherever evaporation of water occurs, the film of hot, dry air touching the meat is cooled by this evaporation, and sinks immediately, to be replaced by a rising film of lighter, hotter, and drier air, which drinks in more vapor, cools and sinks, to give place to another, and so on till the inner juices gradually ooze between the fibers to the porous surface, where they are carried away by the hot, dry air, and a hard, leathery, unmasticable mass of desiccated gelatine, albumen, fibrin, etc., is produced, which, if given to a dog for the purpose of watching its effect on the animal, would render an unlicensed experimenter liable to prosecution under the vivisection act.
Now, let us suppose a similar beefsteak to be cooked by radiant heat, with the least possible co-operation of convection.
To effect this, our source of heat must be a good radiator. Glowing solids are better radiators than ordinary flames; therefore coke, or charcoal, or ordinary coal, after its bituminous matter has done its flaming, should be used, and the steak or chop may be placed in front or above a surface of such glowing carbon. In ordinary domestic practice it is placed on a gridiron above the coal, and therefore I will consider this case first.
The object to be attained is to raise the juices of the meat throughout to about the temperature of 180° Fahr. as quickly as possible, in order that the cookery may be completed before the water of these juices shall have had time to evaporate to any considerable extent; therefore the meat should be placed as near to the surface of the glowing carbon as possible. But the practical housewife will say that, if placed within two or three inches, some of the fat will be melted and burn, and then the steak will be smoked.
Now, here we require a little more chemistry. There is smoking and smoking—smoking that produces a detestable flavor, and smoking that does no mischief at all beyond appearances. The flame of an ordinary coal-fire is due to the distillation and combustion of tarry vapors. If such a flame strikes a comparatively cool surface like that of the meat, it will condense and deposit thereon a film of crude coal-tar and coal-naphtha, most nauseous and rather mischievous; but, if the flame be that which is caused by the combustion of its own fat, the deposit on a mutton-chop will be a little mutton-oil, on a beefsteak a little beef-oil, more or less blackened by mutton-carbon or beef-carbon. But these oils and carbons have no other flavor than that of cooked mutton and cooked beef; therefore they are perfectly innocent, in spite of their guilty black appearances.
If any of my readers are skeptical, let them appeal to experiment, by putting a mutton-chop to the torture, and taking its own confession. To do this, divide the chop in equal halves, then hold one half over a flaming coal, immersing it in the flame, and cook it thus. Now cut a bit of fat off the other, throw this fat on a surface of clear, glowing, flameless coal or coke, and, when a good blaze is thus obtained, immerse this half chop recklessly and unmercifully in this flame; there let it splutter and fizz, drop more fat and make more flame, but hold it there, nevertheless, for a few minutes, and then taste the result.
In spite of its blackness, it will be (if just warmed through to the above-named cooking temperature) a deliciously cooked, juicy, nutritious, digestible morsel, apparently raw, but actually more completely cooked than if it had been held twice as long, at double the distance, from the surface of the fire.
For further instruction, make a third experiment by imitating the cautious unscientific cook, who, ignorant of the difference between the condensation products of coal and those from beef and mutton fat, carefully raises the gridiron directly the flame from the dropping fat threatens the object of her solicitude. The result will be an ordinary domestic chop or steak. I apply this adjective, because, in this particular effort of cookery, the grilling of chops and steaks, domestic cookery is commonly at fault. The majority of our city men find that while the joint cooked at home is better than that they usually get at restaurants and hotels, the chops and steaks are inferior.
I believe that this inferiority is due, in the first place, to the want of understanding of the difference between coal-flame and fat-flame; and in the second, to the advantage afforded to the "grill-room" cook by his specially constructed fire, where a large surface of glowing coke is surmounted by a sloping grill, whereon he can expose his chops and steaks to the radiation from a large glowing surface with a minimum of convection heat, the hot air passing in a current over the coke surface having such small depth that it barely touches the bars of the grill. (This may be seen by watching the course of flame produced by the droppings of the fat.) The same obliquity of draught prevents the serious blacking of the meat, which, although harmless, is unsightly and calculated to awaken prejudice.
The high temperature rapidly imparted by radiation to the surface of the meat forms a thin superficial crust of hardened and semi-carbonized albumen and fiber, which resists the outrush of vapor, and produces within a certain degree of high pressure, which probably acts in loosening the fibers. A well-grilled chop or steak is "puffed" out—made thicker in the middle; an ill-cooked, desiccated specimen is shriveled, collapsed, and thinned by the slow departure of its juices.
Happy little couples, living in little houses with only one little servant—or, happier still, with no servant—complain of their little joints of meat, which, when roasted, are so dry, as compared with the big, succulent joints of larger households. A little reflection on the principles applied in my last to the grilling of steaks and chops will explain the source of this little difficulty, and I think show how it may he overcome.
I will here venture upon a little of the mathematics of cookery, as well as its chemistry. While the weight or quantity of material in a joint increases with the cube of its through-measured dimensions, its surface only increases with their square—or, otherwise stated, we do not nearly double or treble the surface of a joint of given form when we double or treble its weight; and, vice versa, the less the weight, the greater the surface in proportion to the weight. This is obvious enough when we consider that we can not cut a single lump of anything into halves without exposing or creating two fresh surfaces where no surfaces were exposed before. As the evaporation of the juices is, under given conditions, proportionate to the surface exposed, it is evident that this process of converting the inside middle into two outside surfaces must increase the amount of evaporation that occurs in roasting.
What, then, is the remedy for this? It is twofold: First, to seal up the pores of these additional surfaces as completely as possible; and, secondly, to diminish to the utmost the time of exposure to the dry air. Logically following up these principles, I arrive at a practical formula, which will probably induce certain orthodox cooks to denounce me as a culinary paradoxer. It is this: That the smaller the joint to be roasted the higher the temperature to which its surface should be exposed. The roasting of a small joint should, in fact, be conducted in nearly the same manner as the grilling of a chop or steak described in my last. The surface should be crusted or browned—burned, if you please—as speedily as possible, in such wise that the juices within shall be held there under high pressure, and only allowed to escape by burst and splutters, rather than by steady evaporation.
The best way of doing this is a problem to be solved by the practical cook. I only expound the principles, and timidly suggest the mode of applying them. In a metallurgical laboratory, where I am most at home, I could roast a small joint beautifully by suspending it inside a large red-hot steel-melter's crucible, or, better still, in an apparatus called a "muffle," which is a fire-clay tunnel open in front, and so arranged in a suitable furnace as to be easily made red-hot all round. A small joint placed on a dripping-pan and run into this would be equally heated by all-round converging radiation, and exquisitely roasted in the course of about ten to thirty minutes, according to its size. Some such an apparatus has yet to be invented in order that we may learn the flavor and tenderness of a perfectly-roasted small joint of beef or mutton.
For roasting large masses of meat, a different proceeding is necessary. Here we have to contend, not with excessive surface in proportion to bulk—as in the grilling of chops and steaks and the roasting of small joints—but with the contrary—viz., excessive bulk in proportion to surface. If a baron of beef were to be treated according to my prescription for a steak, or for a single wing-rib, or other joint of three to five pounds' weight, it would be charred on its surface long before the heat could reach its center.
A considerable time is here inevitably demanded. Of course, the higher the initial outside temperature, the more rapidly the heat will penetrate; but we can not apply this law to a lump of meat, as we may to a mass of iron. We may go on heating the outside of the iron to redness, but not so the meat. So long as the surface of the meat remains moist, we can not raise it to a higher temperature than the boiling-point of the liquid that moistens it. Above this, charring commences. A little of such charring, such as occurs to the steak or small joint during the short period of its exposure to the great heat, does no harm; it simply "browns" the surface; but if this were continued during the roasting of a large joint, a crust of positively black charcoal would be formed, with ruinous waste and general detriment.
As Rumford proved long ago, liquids are very bad conductors, and when their circulation is prevented by confinement between fibers, as in the meat, the rate at which heat will travel through the humid mass is very slow indeed. As few of my readers are likely to fully estimate the magnitude of this difficulty, I will state a fact that came under my own observation, and at the time surprised me.
About five-and-twenty years ago I was visiting a friend at Warwick during the "mop" or "statute fair"—the annual slave-market of the county. In accordance with the old custom, an ox was roasted whole in the open public market-place. The spitting of the carcass and starting the cookery was a disgusting sight. We are accustomed to see the neatly-cut joints ordinarily brought to the kitchen; but the handling and impaling of the whole body of a huge beast by half a dozen rough men, while its stiffened limbs were stretching out from its trunk, presented the carnivorous character of our ordinary feeding very grossly indeed.
Nevertheless I watched the process, and dined on some of its result. The fire was lighted before midnight, the rotation of the beast on the horizontal spit before it began shortly after, and continued until the following midday, all this time being necessary for the raising of the inner parts of the flesh to the cooking temperature of about 180° Fahr.
Compare this with the grilling of a steak, which, when well done, is done in a few minutes, or the roasting of the small joint as above within thirty minutes, and you will see that I am justified in dwelling on the great differences of the two processes, and the necessity of very varied proceeding to meet these different conditions.
The difference of time is so great that the smaller relative surface is insufficient to compensate for the evaporation that must occur if the grilling principle, or the pure and simple action of radiant heat, were only made available, as in the above ideal roasting of the small joint.
What, then, is added to this? How is the desiccating difficulty overcome in the large-scale roasting? Simply by basting.
All night long and all the next morning men were continuously at work pouring melted fat over the surface of the slowly-rotating carcass of the Warwick ox, skillfully directing a ladleful to any part that indicated undue dryness.
By this device the meat is more or less completely enveloped in a varnish of hot melted fat, which assisted in the communication of heat while it checked the evaporation of the juices. In such roasting the heat is partially communicated by convection through the medium of a fat-bath, as in stewing it is all supplied by a water-bath.
I purpose making an experiment, whereby this principle will be fully carried out. I shall melt a sufficient quantity of mutton-fat to form a bath, in which a small joint of mutton may be immersed, or of beef-fat for beef; and then keep the melted fat at about the cooking temperature, or a little above it—say the boiling-point of water, which will be indicated by the spluttering due to the evaporation of the water in the meat. The result of this experiment will be duly reported to the readers of "Knowledge" when I reach the general subject of frying. In my next I must continue this subject of roasting, which is by no means exhausted yet. Count Rumford devotes seventy pages to it, and I quote his words for my own use. He says: "I shall, no doubt, be criticised by many for dwelling so long on a subject which to them will appear low, vulgar, and trifling; but I must not be deterred by fastidious criticisms from doing all I can do to succeed in what I have undertaken. Were I to treat my subject superficially, my writing would be of no use to anybody, and my labor would be lost; but by investigating it thoroughly I may, perhaps, engage others to pay that attention to it which, from its importance, it deserves."—Knowledge.
- "Essays Political, Economical, and Philosophical," vol. iii, p. 129.