Popular Science Monthly/Volume 24/January 1884/The Chemistry of Cookery VIII
|THE CHEMISTRY OF COOKERY.|
IN my last I described generally the diffusion of liquids, and the actions to which the names of endosmosis and exosmosis have been given. It is easily seen that in extracting the juices of meat by immersion in water the work is done by these two agencies. This is the case, whether the extraction is effected by maceration (immersion in cold water) or by stewing.
Some of these juices, as already explained, exist between the fibers of the meat, others are within those fibers or cells, enveloped in the sheath or cell-membrane. It is evident that the loose or free juices will be extracted by simple diffusion; those enveloped in membranes by exosmosis through the membrane. The result must be the same in both cases: the meat will be permeated by the water, and the surrounding water will be permeated by the juices that originally existed within the meat. As the rate of diffusion—other conditions being equal—is proportionate to the extent of the surfaces of the diverse liquids that are exposed to each other, and, as the rate of osmosis is similarly proportioned to the exposure of membrane, it is evident that the cutting-up of the meat will assist the extraction of its juices by the creation of fresh surfaces; hence the well-known advantage of mincing in the making of beef-tea.
It is interesting to observe the condition of lean meat that has thus been minced and exposed for a few hours to these actions by immersion in cold water. On removing and straining such minced meat it will be found to have lost its color, and if it is now cooked it is insipid, and even nauseous if eaten in any quantity. It has been given to dogs and cats and pigs; these, after eating a little, refuse to take more, and, when supplied with this juiceless meat alone, they languish, become emaciated, and die of starvation if the experiment is continued. Experiments of this kind contributed to the fallacious conclusions described in No. 6 of this series. Although the meat from which the juices are thus completely extracted is quite worthless alone, and meat from which they are partially extracted is nearly worthless alone, either of them becomes valuable when eaten with the juices. The stewed beef of the Frenchman would deserve the contempt bestowed upon it by the prejudiced Englishman if it were eaten as the Englishman eats his roast beef; but when preceded by a potage containing the juices of the beef it is quite as nutritious as if roasted, and more easily digested.
Graham found that increase of temperature increased the rate of diffusion of liquids, and in accordance with this the extraction of the juices of meat is effected more rapidly by warm than by cold water, but there is a limit to this advantage, as will be easily understood by referring back to No. 3, in which are described the conditions of coagulation of one of these juices—viz., the albumen, which at the temperature of 134° Fahr. begins to show signs of losing its fluidity; at 160° becomes a semi-opaque jelly; and at the boiling-point of water is a rather tough solid, which, if kept at this temperature, shrinks, and becomes harder and harder, tougher and tougher, till it attains a consistence comparable to that of horn tempered with gutta-percha.
I have spoken of beef-tea, or Extractum Camis (Liebig's Extract of Meat), as an extreme case of extracting the juices of meat, and must now explain the difference between this and the juices of an ordinary stew. Supposing the juices of the meat to be extracted by maceration in cold water, and the broth thus obtained to be heated in order to alter its raw flavor, a scum will be seen to rise upon the surface; this is carefully removed in the manufacture of Liebig's extract or the preparation of beef-tea for an invalid, but in thus skimming we remove a highly-nutritious constituent—viz., the albumen which has coagulated during the heating. The pure beef-tea, or Extractum Carnis, contains only the creatine, creatinine, the soluble phosphates, the lactic acid, and other non-coagulable saline constituents, that are rather stimulating than nutritious, and which, properly speaking, are not digested at all—i. e., they are not converted into chyme in the stomach, do not pass through the pylorus into the duodenum, etc., but, instead of this, their dilute solution passes, like the water we drink, directly into the blood by endosmosis through the delicate membrane of that marvelous network of microscopic blood-vessels which is spread over the surface of every one of the myriads of little upstanding filaments which, by their aggregation, constitute the villous or velvet coat of the stomach. In some states of prostration, where the blood is insufficiently supplied with these juices, this endosmosis is like pouring new life into the body, but it is not what is required for the normal sustenance of the healthy body.
For ordinary food, all the nutritious constituents should be retained, either in the meat itself, or in its liquid surrounding. Regarding it theoretically, I should demand the retention of the albumen in the meat, and insist upon its remaining there in the condition of tender semi-solidity, corresponding to the white of an egg when perfectly cooked, as described in No. 4. Also that the gelatine and fibrine be softened by sufficient digestion in hot water, and that the saline juices (those constituting beef-tea) be partially extracted. I say "partially," because their complete extraction, as in the case of the macerated mince-meat, would too completely rob the meat of its sapidity. How, then, may these theoretical desiderata be attained?
It is evident from the principles already expounded that cold extraction takes out the albumen, therefore this must be avoided; also that boiling water will harden the albumen to leathery consistence. This may be shown experimentally by subjecting an ordinary beef-steak to the action of boiling water for about half an hour. It will come out in the abominable condition too often obtained by English cooks when they make an attempt at stewing—an unknown art to the majority of them. Such an ill-used morsel defies the efforts of ordinary human jaws, and is curiously curled and distorted. This toughening and curling is a result of the coagulation, hardening, and shrinkage of the albumen, as described in No. 3.
It is evident, therefore, that in stewing, neither cold water nor boiling water should be used, but water at the temperature at which albumen just begins to coagulate—i. e., about 134°, or between this and 160° as the extreme. But here we encounter a serious difficulty. How is the unscientific cook to determine and maintain this temperature? If you tell her that the water must not boil, she shifts her stew-pan to the side of the fire, where it shall only simmer, and she firmly believes that such simmering water has a lower temperature than water that is boiling violently over the fire. "It stands to reason" that it must be so, and, if the experimental philosopher appeals to fact and the evidence of the thermometer, he is a "theorist."
The French cook escapes this simmering delusion by her common use of the bain-marie or "water-bath," as we call it in the laboratory, where it is also largely used for "digesting" at temperatures below 212°. This is simply a vessel immersed in an outer vessel of water. The water in the outer vessel may boil, but that in the inner vessel can not, as its evaporation keeps it below the temperature of the water from which its heat is derived. A carpenter's glue-pot is a very good and compact form of water-bath, and I recommend the introduction of this apparatus into kitchens where a better apparatus is not obtainable. Some iron-mongers keep in stock a form of water-bath which they call a "milk-scalder." This resembles the glue-pot, but has an inner vessel of earthenware, which is, of course, a great improvement upon the carpenter's device, as it may be so easily cleaned.
One of the incidental advantages of the bain-marie is that the stewing may be performed in earthenware or even glass vessels, seeing that they are not directly exposed to the fire. Other forms of such double vessels are obtainable at the best iron-mongers'. I have lately seen a very neat apparatus of this kind, called "Dolby's Extractor." This consists of an earthenware vessel that rests on a ledge, and thus hangs in an outer tin-plate vessel; but, instead of water, there is an air-space surrounding the earthenware pot. A top screws over this, and the whole stands in an ordinary saucepan of water. The heat is thus very slowly and steadily communicated through an air-bath, and it makes excellent beef-tea; but, being closed, the evaporation does not keep down the temperature sufficiently to fulfill the above-named conditions for perfect stewing. At temperatures below the boiling-point evaporation proceeds superficially, and the rate of evaporation at a given temperature is proportionate to the surface exposed, irrespective of the total quantity of water; therefore, the shallower the inner vessel of the bain-marie, and the greater its upper outspread, the lower will be the temperature of its liquid contents when its sides and bottom are heated by boiling water. The water in a basin-shaped inner vessel will have a lower temperature than that in a vessel of similar depth, with upright sides, and exposing an equal water-surface. A good water-bath for stewing may be extemporized by using a common pudding-basin (I mean one with projecting rim, as used for tying down the pudding-cloth), and selecting a saucepan just big enough for this to drop into, and rest upon its rim. Put the meat, etc., to be stewed into the basin, pour hot water over them, and hot water into the saucepan, so that the basin shall be in a water-bath; then let this outer water simmer—very gently, so as not to jump the basin with its steam. Stew thus for about double the time usually prescribed in English cookery-books, and compare the result with similar materials stewed in boiling or "simmering" water.
In my last I explained the hardening effect of boiling water on meat, and the consequent necessity of keeping down the temperature considerably below the boiling-point in order to obtain a tender and full-flavored stew. Some further explanation is necessary, as it is quite possible to obtain what commonly passes for tenderness by a very flagrant violation of the principles there expounded. This is done on a large scale and in extreme degree in the preparation of ordinary Australian tinned meat. A number of tins are filled with the meat, and soldered down close, all but a small pin-hole. They are then placed in a bath charged with a saline substance, such as chloride of zinc, which has a higher boiling-point than water. This is heated up to its boiling-point, and consequently the water which is in the tins with the meat boils vigorously, and a jet of steam mixed with air blows from the pin-hole. When all the air is expelled and the jet is of pure steam only (a difference detected at once by the trained expert), the tin is removed, and a little melted solder skillfully dropped on the hole to seal the tin hermetically. An examination of one of these tins will show this final soldering with—in some—a flap below to prevent any solder from falling in among the meat. The object of this is to exclude all air, for, if only a very small quantity remains, oxidation and putrefaction speedily ensue, as shown by a bulging of the tins instead of the partial collapse that should occur when the steam condenses, the display of which collapse is an indication of good quality of the contents.
By "good quality" I mean good of its kind; but, as everybody knows who has tried beef and mutton thus prepared, it is not satisfactory. The preservation from putrefactive decomposition is perfectly successful, and all the original constituents of the meat are there. It is apparently tender, but practically tough—i. e., it falls to pieces at a mere touch of the knife, but these fragments offer to the teeth a peculiar resistance to proper masticatory comminution. I may describe their condition as one of pertinacious fibrosity. The fibers separate, but there they are as stubborn fibers still.
This is a very serious matter, for, were it otherwise, the great problem of supplying our dense population with an abundance of cheap animal food would have been solved about twenty years ago. As it is, the plain tinned-meat enterprise has not developed to any important extent beyond affording a variation with salt junk on board ship.
What is the rationale of this defect? Beyond the general statement that the meat is "overdone," I have met with no attempt at explanation; but am not, therefore, disposed to give up the riddle without attempting a solution.
Reverting to what I have already said concerning the action of heat on the constituents of flesh, it is evident that in the first place the long exposure to the boiling-point must harden the albumen. Syntonin, or muscle-fibrine, the material of the ultimate contractile fibers of the muscle, is coagulated by boiling water, and further hardened by continuous boiling, in the same manner as albumen. Thus, the muscle-fibers themselves and the lubricating liquor in which they are imbedded must be simultaneously toughened by the method above described, and this explains the pertinacious fibrosity of the result.
But how is the apparent tenderness, the facile separation of the fibers of the same meat, produced? A little further examination of the anatomy and chemistry of muscle will, I think, explain this quite satisfactorily. The ultimate fibers of the muscles are enveloped in a very delicate membrane; a bundle of these is again enveloped in a somewhat stronger membrane (areolar tissue); and a number of these bundles or fasciculi are further enveloped in a proportionally stronger sheath of similar membrane. All these binding membranes are mainly composed of gelatine, or the substance which (as explained in No. 5) produces gelatine when boiled. The boiling that is necessary to drive out all the air from the tins is sufficient to dissolve this, and effect that easy separability of the muscular fibers, or fasciculi of fibers, that gives to such overcooked meat its fictitious tenderness.
I have entered into these anatomical and chemical details because it is only by understanding them that the difference between true tenderness and spurious tenderness of stewed meat can be soundly understood, especially in this country, where stewed meats are despised because scientific stewing is practically and generally an unknown art. Ask an English cook the difference between boiled beef or mutton and stewed beef or mutton, and in ninety-nine cases out of a hundred her reply will be to the effect that stewed meat is that which has been boiled or simmered for a longer time than the boiled meat.
She proceeds, in accordance with this definition, when making an Irish stew or similar dish, by "simmering" at 212° until, by the coagulation and hardening of the albumen and syntonin, a leathery mass is obtained; then she continues the simmering until the gelatine of the areolar tissue is dissolved, and the toughened fibers separate or become readily separable. Having achieved this disintegration, she supposes the meat to be tender, the fact being that the fibers individually are tougher than they were at the leathery stage. The mischief is not limited to the destruction of the flavor of the meat, but includes the destruction of the nutritive value of its solid portion by rendering it all indigestible, with the exception of the gelatine which is dissolved in the gravy. This exception should be duly noted, inasmuch as it is the one redeeming feature of such proceeding that renders it fairly well adapted for the cookery of such meat as cow-heels, sheep's trotters, calves'-heads, shins of beef, knuckles of veal, and other viands which consist mainly of membranous, tendinous, or integumentary matter composed of gelatine. To treat the prime parts of good beef or mutton in this manner is to perpetrate a domestic atrocity.
I am not yet able to record the result of stewing a sirloin of beef in accordance with the scientific principles expounded in my last. Have no hopes of being able to do so until I can spare time to stand by the kitchen fire with thermometer in hand from beginning to end of the process, or have constructed a stewing-pot, big enough for the purpose, so arranged that its contents can not possibly by any effort of ingenious perversity be raised above 180°. The domestic superstition concerning simmering is so wide-spread and inveterate that every normally-constituted cook stubbornly believes that simmering water is of much lower temperature than boiling water, and therefore any amount of instruction or injunctions for the maintenance of a heat below boiling will be stubbornly translated into an order for "gentle simmering," a quarter of an hour of which would spoil the sirloin.
I may, however, mention an experiment that I have made lately. I killed a superannuated hen—more than six years old, but otherwise in very good condition. Cooked in the ordinary way she would have been uneatably tough. Instead of being thus cooked, she was gently stewed about four hours. I can not guarantee to the maintenance of the theoretical temperature, having suspicion of some simmering. After this she was left in the water until it cooled, and on the following day was roasted in the usual manner, i. e., in a roasting-oven. The result was excellent; as tender as a full-grown chicken roasted in the ordinary way, and of quite equal flavor, in spite of the very good broth obtained by the preliminary stewing. This surprised me. I anticipated the softening of the tendons and ligaments, but supposed that the extraction of the juices would have spoiled the flavor. It must have diluted it, and that so much remained was probably due to the fact that an old fowl is more fully flavored than a young chicken. The usual farmhouse method of cooking old hens is to stew them simply; the rule in the midlands being one hour in the pot for every year of age. The feature of the above experiment was the supplementary roasting. As the laying season is now coming to an end, old hens will soon be a drug in the market, and those among my readers who have not a hen-roost of their own will oblige their poulterers by ordering a hen that is warranted to be four years old or upward. If he deals fairly he will supply a specimen upon which they may repeat my experiment, very cheaply. It offers the double economy of utilizing a nearly waste product and obtaining chicken-broth and roast fowl simultaneously.
One of the great advantages of stewing is that it affords a means of obtaining a savory and very wholesome dish at a minimum of cost. A small piece of meat may be stewed with a large quantity of vegetables, the juice of the meat savoring the whole. Besides this, it costs far less fuel than roasting.
The wife of the French or Swiss landed proprietor, i. e., the peasant, cooks the family dinner with less than a tenth of the expenditure of fuel used in England for the preparation of an inferior meal. A little charcoal under her bain-marie does it all. The economy of time corresponds to the economy of fuel, for the mixture of viands required for the stew once put into the pot is left to itself until dinner-time, or at most an occasional stirring of fresh charcoal into the embers is all that is demanded.—Knowledge.
- I have ventured to ascribe this lubricating function to the albumen which envelops the fibers, though doubtful whether it is quite orthodox to do so. Its identity in composition with the synovial liquor of the joints and the necessity for such lubricant justify this supposition. It may act as a nutrient fluid at the same time.