Popular Science Monthly/Volume 23/September 1883/The Chemistry of Cookery IV
|THE CHEMISTRY OF COOKERY.|
AS stated in my last, the subject of roasting occupied a large amount of Count Rumford's attention, especially while he was in England residing in Brompton Road, and founding the Royal Institution. His efforts were directed not merely to cooking the meat effectively, but to doing so economically. Like all others who have contemplated thoughtfully the habits of Englishmen, he was shocked at the barbaric waste of fuel that everywhere prevailed in this country, even to a greater extent then than now.
The first fact that necessarily presented itself to his mind was the great amount of heat that is wasted, when an ordinary joint of meat is suspended in front of an ordinary coal-fire to intercept and utilize only a small fraction of its total radiation.
As far as I am aware, there is no other country in Europe where such a process is indigenous. I say "indigenous" because there certainly are hotels where this or any other English extravagance is perpetrated to please Englishmen who choose to pay for it. What is usually called roast meat in countries not inhabited by English-speaking people is what we should call "baked meat," the very name of which sets all the gastronomic bristles of an orthodox Englishman in a position of perpendicularity.
I have a theory of my own respecting the origin of this prejudice. Within the recollection of many still living, the great middle class of Englishmen lived in town; their sitting-rooms were back parlors behind their shops, or factories, or warehouses, their drawing-rooms were on the first-floor, and kitchens in the basement.
They kept one general servant of the "Marchioness" type. The corresponding class now live in suburban villas, keep cook, house-maid, and parlor-maid, besides the gardener and his boy, and they dine at supper-time.
In the days of the one marchioness and the basement kitchen, these citizens "of credit and renown" dined at dinner-time, and were in the habit of placing a three-legged open iron triangle in a brown earthenware dish; then spreading a stratum of peeled potatoes on said dish, and a joint of meat above, on the open triangular support. The combination was carried by the marchioness to the bakehouse round the corner at about 11 a. m., and brought back steaming and savory at 1 p. m.
This was not done always, but at other times, as when the condition of the mistress's wardrobe offered no particular motive for going to church, she staid at home and roasted the Sunday dinner. The experience thus obtained demonstrated a material difference between the flavor of the roasted and the baked meat very decidedly in favor of the home-roasted. Why?
The principal reason was, I believe, that the baker's large bread oven contained at dinner-time a curious medley of meats—mutton, beef, pork, geese, veal, etc., including stuffing with sage and onions, besides the possibility of a joint or two that had been hung longer than was necessary for procuring tenderness. The vapors of these would induce a confusion of flavors in the milder meats, fully accounting for the observed superiority of the home-roasted joints.
A little reflection on the principles already expounded will show that, theoretically regarded, a given piece of meat would be better roasted in a closed chamber radiating heat from all sides toward the meat than it could be when suspended in front of a fire and heated only on one side, while the other side was turned away to cool more or less, according to the rate of rotation.
If I agreed with the popular belief in the advantage of open-air exposure to direct radiation from glowing coal, I should suggest that for large joints a special roasting fire be constructed, by building an upright cylinder of fire-brick, and erecting within this a smaller cylinder or grating of iron bars, so that the fuel should be placed between these, and thus form an upright cylindrical ring or shirt of fire, inclosed outside by the bricks, but open and glowing toward the inside of the hollow cylinder, in the midst of which the meat should be suspended to receive the radiation from all sides.
The whole apparatus might stand under a dome, terminating in an ordinary chimney, like a glass-house or a steel-maker's cementing furnace; or, in this respect, like those wondrous kitchens of the old seraglio, to which I have already alluded, where each apartment is a huge chimney, outspreading downward, so that the cooks and their materials and apparatus, as well as the huge fires themselves, are all under the great central chimney-shaft.
I do not, however, recommend such an apparatus, even to the most wealthy and luxurious epicure, because I am convinced, not merely from theoretical considerations, but also from practical experiments, that all kinds of meat may be not merely as well roasted in a close oven as before an open fire, but that the close chamber, properly managed, produces better results in every respect than can possibly be obtained by roasting in the open air.
To obtain such results there must be no compromise, no concession to any false theory respecting a necessity for ventilation.
Many modern kitchen-ranges are fitted with such compromises in the shape of a ventilated roasting-oven, the action of which ventilation is purely and simply mischievous, excepting in the case of semi-putrid game or venison, which require to be carbonized and disinfected as well as cooked, and, of course, also demand the speedy removal of their noxious vapors.
Not so with fresh meats. There is nothing in the vapor of beef that can injure the flavor of beef, nor in the vapor of mutton that is damaging to mutton, and so on with the rest. But there is much that can, and does, actually improve them; or, more strictly speaking, prevents the deterioration to which they are liable when roasted before an open fire. I will endeavor to explain this.
Carefully-conducted experiments have demonstrated the general law that atmospheric air is a vacuum to the vapor of water and other similar vapors, while each particular vapor is a plenum to itself, though not to other vapors; or, otherwise stated, if a given space, at a given temperature, be filled with air, the quantity of aqueous vapor that it is capable of holding is the same as though this space contained no air at all, nor anything else. But this same space may contain a much smaller quantity of aqueous vapor, and yet be absolutely impenetrable to aqueous vapor, provided its temperature is unaltered.
Thus, if a bell-glass, filled with air under ordinary pressure, at the temperature of 100° Fahr., be placed over a dish of water at same temperature, a quantity of vapor, equal to one thirtieth (in round numbers) of the weight of the air, will rise into the bell-glass, and there remain diffused throughout. If there were less air, or no air at all (temperature remaining the same), the bell-glass would obtain and hold the same quantity of vapor.
If, instead of being filled with air, it contained at the outset only this one thirtieth of aqueous vapor, it would now be an impenetrable plenum, behaving like a solid to aqueous vapor—no more can be forced into it without raising its temperature.
But while thus charged with aqueous vapor, there would still be room for vapor of alcohol, or turpentine, or ether, or chloroform, etc. It would be a vacuum to these, though a plenum to itself. On the other hand, if the alcohol, turpentine, ether, or chloroform were allowed to evaporate into the bell-glass, a certain quantity of either of these vapors would presently enter it, and then this vapor would act like a solid mass in resisting the entry of any more of its own kind, while it would be freely pervious to the vapor of water or that of the other liquids.
A practical example will further illustrate this. Some years ago I was engaged in the distillation of paraffin-oil, and had a few thousand gallons of the crude liquid in a still with a tall head and a rising condenser. In spite of severe firing, the distillation proceeded very slowly. Then I threw into the still, just above the surface of the oil, a jet of steam. The rate of distillation immediately increased with the same firing, although the steam was of much lower temperature than the boiling oil, and therefore wasted much heat. The rationale of this was that at first an atmosphere of oil-vapor stood over the oil, and this was impervious to more oil-vapor, but, on sweeping this out and replacing it by steam, the atmosphere above the liquid oil was permeable by oil-vapor. This principle is largely applied in similar distillations.
But I am exceeding my limits, and must, therefore, defer the direct application of these principles to my next, though doubtless most of my readers w r ill anticipate, or, in vulgar but expressive phrase, "see what I am driving at."
Always keeping in view that the primary problem in roasting is to raise the temperature throughout to the cooking heat with the smallest possible degree of desiccation of the natural juices of the meat, and applying to this problem the laws of vapor diffusion expounded in my last, it is easy enough to understand the theoretical advantages of roasting in a closed oven, the space within which speedily becomes saturated with those particular vapors that resist further vaporization of these juices.
I say "theoretical," because I despair of practically convincing any thorough-bred Englishman that baked meat is better than roasted meat by any reasoning whatever. If, however, he is sufficiently "un-English" to test the question experimentally, he may possibly convince himself. To do this fairly, a large joint of meat should be equally divided, one half roasted in front of the fire, the other in a non-ventilated oven over a little water by a cook who knows how to heat the latter. This condition is essential, as some intelligence is demanded in regulating the temperature of an oven, while any barbarian can carry out the modern modification of the ordinary device of the savage, who skewers a bit of meat, and holds this near enough to a fire to make it frizzle.
Having settled this question to my own satisfaction more than twenty years ago, I now amuse myself occasionally by experimenting upon others, and continually find that the most uncompromising theoretical haters of baked meat practically prefer it to orthodox roasted meat, provided always that they eat it in ignorance.
Part II of Count Rumford's "Tenth Essay" is devoted to his roaster and roasting generally, and occupies ninety-four pages, including the special preface. This preface is curious now, as it contains the following apology for delay of publication: "During several months, almost the whole of my time was taken up with the business of the Royal Institution; and those who are acquainted with the objects of that noble establishment will, no doubt, think that I judged wisely in preferring its interest to every other concern." To those who have attended the fashionable gatherings held on Friday evenings in "that noble establishment" during the London season, it is almost comical to read what its founder says concerning the object for which it was instituted, viz., the noble purpose of DIFFUSING THE KNOWLEDGE AND FACILITATING THE GENERAL INTRODUCTION OF NEW AND USEFUL INVENTIONS AND IMPROVEMENTS." The capitals are Rumford's, and he illustrates their meaning by reference to "the repository of this new establishment," where specimens of pots and kettles, ovens, roasters, fireplaces, gridirons, tea-kettles, kitchen-boilers, etc., might be inspected.
Some years ago, when I was sufficiently imprudent to accept an invitation to describe Rumford's scientific researches in one Friday evening lecture, rigidly limited to fifty-seven minutes (and consequently muddled my subject in the vain struggle to condense it), I tried to find the original roaster, but failed; all that remained of the original "repository" being a few models put out of the way as though they were empty wine-bottles. I am not finding fault, as the noble work that has been done there by Davy, Faraday, and Tyndall must have profoundly gladdened the supervising soul of Rumford (supposing that it does such spiritual supervision), in spite of his neglected roaster, which I must now describe without further digression.
It is shown open and out of its setting in Fig. 1, and there seen as a hollow cylinder of sheet-iron, which for ordinary use may be about eighteen inches in diameter and twenty-four inches long, closed permanently at one end, and by a hinged double door of sheet-iron (d d) at the other. This doubling of the door is for the purpose of retaining Fig. 2. Fig. 3. Fig. 4.the heat by means of an intervening lining of ill-conducting material. Or a single door of sheet-iron, with a panel of wood outside, may be used. The whole to be set horizontally in brickwork, as shown in Fig. 4, the door-front being flush with the front of the brickwork. The flame of the small fire below plays freely all round it by filling the enveloping flue-space indicated by the dotted lines on Fig. 4. Inside the cylinder is a shelf to support the dripping-pan (d), Fig. 1, which is separately shown in Figs. 2 and 3.
This dripping-pan is an important element of the apparatus. Fig. 3 shows it in cross-section, made up of two tin-plate dishes, one above the other, arranged to leave a space (w) between. This space contains water, half to three quarters of an inch in depth. Above is a gridiron, shown in plan, Fig. 2, on which the meat rests; the bars of this are shown in section in Fig. 3. The object of this arrangement is to prevent the fat which drips from the meat from being overheated and filling the roaster with the fumes of "burnt," i. e., partially decomposed, . fat and gravy, to the tainting influence of which Rumford attributed the English prejudice against baked meat. So long as any water remains, the dripping can not be raised more than two or three degrees above 212°. The tube v, Fig. 1, is for carrying away vapor, if necessary. This tube may be opened or closed by means of a damper moved by the little handle shown on the right. The heat of the roaster is regulated by means of the register c in the ash-pit door of the fireplace, its dryness by the above-named damper of the steam-tube v, and also by the blow-pipes, b p.
These are iron tubes, about two and a half inches in diameter, placed underneath, so as to be in the midst of the flame as it ascends from the fire into the enveloping flue, shown by the dotted lines, Fig. 4, where their external openings are shown at b p, b p, and the plugs by which they may be opened or closed in Fig. 1. It is evident that by removing these plugs and opening the damper of the steam-pipe a blast of hot, dry air will be delivered into the roaster at its back part, and it must pass forward to escape by the steam-pipe. As these blow-pipes are raised to a red heat when the fire is burning briskly, the temperature of this blast of air may be very high; with even a very moderate fire, sufficiently high to desiccate and spoil the meat if they were kept open during all the time of cooking. They are accordingly to be kept closed until the last stage of the roasting is reached; then the fire is urged by opening the ash-pit register, and when the blow-pipes are about red-hot their plugs are removed, and the steam-pipe damper is opened for a few minutes to brown the meat by means of the hot wind thus generated.
It will be observed that a special fire directly under the roaster is here designed, and that this fire is inclosed in brickwork. This is a general feature of Rumford's arrangements, which I shall have to discuss more fully when I come to the subject of kitchen-fires. The economy of the whole device will be understood by the fact that, in a test experiment at the Foundling Institution of London, he roasted one hundred and twelve pounds of beef with a consumption of only twenty-two pounds of coal (three pennyworth, at twenty-five shillings per ton).
Rumford tells us that "when these roasters were first proposed, and before their merit was established, many doubts were entertained respecting the taste of the food prepared in them," but that, after many practical trials, it was proved that "meat of every kind, without any exception, roasted in a roaster, is better tasted, higher flavored, and much more juicy and delicate than when roasted on a spit before an open fire." These italics are in the original, and the testimony of competent judges is quoted.
I must describe one experiment in detail. Two legs of mutton from the same carcass made equal in weight before cooking were roasted, one before the fire and the other in a roaster. When cooked both were weighed, and the joint roasted in the roaster proved to be heavier than the other by six per cent. They were brought upon table at the same time, "and a large and perfectly unprejudiced company was assembled to eat them." Both were found good, but a decided preference given to that cooked in the roaster; "it was much more juicy, and was thought better tasted." Both were fairly eaten up, nothing remaining of either that was eatable, and the fragments collected. "Of the leg of mutton which had been roasted in the roaster, hardly anything visible remained, excepting the bare bone; while a considerable heap was formed of scraps not eatable which remained of that roasted on a spit."
This was an eloquent experiment; the six per cent gained tell of juices retained with consequent gain of flavor, tenderness, and digestibility, and the subsequent testimony of the scraps describes the difference in the condition of the tendonous, integumentary portions of the joints, which are just those that present the toughest practical problems to the cook, especially in roasting.
But why are these roasters not in general use? Why did they die with their inventor? I will take up these questions in my next.
Returning to the question suggested by my last paper, Why has Rumford's roaster fallen into disuse, notwithstanding the fact, mentioned in his essay, that Mr. Hopkins, of Greek Street, Soho, had sold above two hundred, and others were making them?
Those of my readers who have had practical experience in using hot air or in superheating steam, will doubtless have already detected a weak point in the "blow-pipes." When iron pipes are heated to redness, or thereabout, and a blast of air or steam passes through them, they work admirably for a while, but presently the pipe gives way, for iron is a combustible substance, and burns slowly when heated and supplied with abundant oxygen, either by means of air or water, the latter being decomposed, its hydrogen set free, while its oxygen combines with the iron and reduces it to friable oxide. Rumford does not appear to have understood this, or he would have made his blowpipes of fire-clay or other refractory non-oxidizable material.
The records of the Great Seal Office contain specifications of hundreds of ingenious inventions that have failed most vexatiously from this defect; and I could tell of joint-stock companies that have been "floated" to carry out inventions involving the use of heated air or superheated steam that have worked beautifully and with apparent economy while the shares were in the market, and then collapsed just when the calls were paid up, the cost of renewal of super-heaters and hot-air chambers having worse than annulled the economy of working fuel described in the prospectus. Thus a vessel driven by heated air, as a substitute for steam, was fitted up with its caloric engine, and crossed the Atlantic with passengers on board. The voyage practically demonstrated a great saving of coal; patent rights were purchased accordingly for a very large amount, and shares went up buoyantly until the oxidation of the great air-chamber proved that the engine burned iron as well as coal at a ruinous cost.
Although no mention is made by Rumford of such destruction of the blow-pipes, he was evidently conscious of the costliness of his original roaster, as he describes another which may be economically substituted for it. This has an air-chamber formed by bringing the body of the oven-door so as to inclose the space occupied by the blowpipes shown in Fig. 1, and placing the dripping-pan on a false bottom joined to the front face of the roaster just below the door, but not extending quite to the back. An adjustable register door opens at the front into this air-chamber, and when this is opened the air passes along from front to back under the false bottom, and rises behind to an outlet pipe like that shown at v, Fig. 1. In thus passing along the hot bottom of the oven the air is heated, but not so greatly as by the blow-pipes, which, being surrounded by the flame on all sides, are heated above as well as below, and the air in passing through them is much more exposed to heat than in passing through the air-chamber.
To increase the heat transmitted in the latter, Rumford proposes that "a certain quantity of iron wire, in loose curls, or of iron turnings, be put into the air-chamber."
This modification he called a "roasting-oven," to distinguish it from the first described, the "roaster." He states that the roasting oven is not quite so effective as the roaster, but from its greater cheapness may be largely used. This anticipation has been realized. The modern "kitchener," which in so many forms is gradually and steadily supplanting the ancient open range, is an apparatus in which roasting in the open air before a fire is superseded by roasting in a closed chamber or roasting oven. Having made three removals within the last twelve years, each preceded by a tedious amount of house-hunting, I have seen a great many kitchens of newly-built houses, and find that about ninety per cent of these have closed kitcheners, and only about ten per cent are fitted with open ranges of the old pattern. Bottle-jacks, like smoke-jacks and spits, are gradually falling into disuse.
When these kitcheners were first introduced, a great point was made by the manufacturer of the distinction between the roasting and the baking oven; the first being provided with a special apparatus for effecting ventilation by devices more or less resembling that in Rumford's roasting-oven. Gradually these degenerated into mere shams, and now in the best kitcheners even a pretense to ventilation is abandoned. Having reasoned out my own theory of the conditions demanded for perfect roasting some time ago (about 1860, when I lectured on "Household Philosophy" to a class of ladies at the Birmingham and Midland Institute), I have watched the gradual disappearance of these concessions to popular prejudice with some interest, as they show how practical experience has confirmed this theory, which, as already expounded, is that the meat should be cooked by the action of radiant heat, projected toward it from all sides, while it is immersed in an atmosphere saturated with its own vapors.
Herein I diverge from ray teacher, as the preceding description of both his roaster and roasting-oven shows. His explanation of the prejudice of Englishmen against baked meats may have been to some extent justified by his own experience, seeing that he heated his ovens by a fire placed below, and, if he first used these without his water-pan, they doubtless effected the decomposition of the dripping and gravy of which he speaks (see No. XI of this series, page 591); but even in this case the flavor of merely burned fat is not very serious—far less objectionable than that of the vile mixture of vapors described in No. X.
The few domestic fireplace ovens that existed in Rumford's time were clumsily heated by raking some of the fire from the grate into a space left below the oven. Those of the best modern kitcheners are heated by flues going round them, generally starting from the top, which thus attains the highest temperature. The radiation from this does the "browning" for which Rumford's blow-pipes were designed.
According to my view of the philosophy of roasting, this browning, or the application of the highest temperature, should take place at the beginning rather than the end of the process, in order that a crust of firmly coagulated albumen may surround the joint and retain the juices of the meat. All that is necessary to obtain this effect in a sufficient degree is to raise the roasting-oven to its full temperature before the meat is put in. Supposing an equal fire is maintained all the while, this initial temperature will exceed that of the continuing temperature, because, when the meat is in the oven, the radiant heat from its sides are intercepted by the joint and doing work upon it; heat can not do work without a corresponding fall of temperature. While the oven is empty, the radiations from each side cross the open space to re-enforce the temperature of the other sides.
Is there, then, any difference at all between roasting and baking? There is. In roasting, the temperature, after the first start, is maintained about uniformly throughout; while, in baking by the old-fashioned method, the temperature continually declines from the beginning to the end of the process; but, in order that a dweller in cities, or the cook of an ordinary town household, may understand this difference, some explanation is necessary. The old-fashioned oven, such as was generally used in Rumford's time, and is still used in country houses and by old-fashioned bakers, was an arched cavity of brick, with a flat brick floor. This cavity is closed by a suitable door, which, in its primitive and perhaps its best form, was a flat tile that was pressed against the opening, and luted round with clay. Such ovens were, and still are, heated by simply spreading on the brick floor a sufficient quantity of wood—preferably well-dried twigs; these, being lighted, raise the temperature of the arched roof to a glowing heat, and that of the floor in a somewhat lower degree. When this heating is completed (the judgment of which constitutes the chief element of skill in thus baking) the embers are carefully brushed out from the floor, the loaves, etc., inserted by means of a flat battledoor with a long handle, called a "peel," and the door closed and firmly luted round, not to be opened until the operation is complete. Baked clay is an excellent radiator, and, therefore, the surface of bricks forming the arched roof of the oven radiates vigorously upon its contents below, which are thus heated at top by radiation from the roof, and at bottom by direct contact with the floor of the oven. The difference between the compact bottom crust and the darker, bubble-bearing top crust of an ordinary loaf is thus explained.
As the baking of a large joint of meat is a longer operation than the baking of bread, there is another reason besides that already given for the inferiority of meat when baked in a baker's oven constructed on this principle. The slow cooling down must tend to produce a flabbiness and insipidity similar to those of the roast meat which is served at restaurants, where a joint remains "in cut" for two or three hours. Of this I speak theoretically, not having had an opportunity of tasting a joint that has been cooked in a brick oven of the construction above described, but have observed the advantage of maintaining a steady heat throughout the process of roasting in the iron oven of a kitchener, or American stove, or gas-oven.