Popular Science Monthly/Volume 23/June 1883/The Chemistry of Cookery I
|THE CHEMISTRY OF COOKERY.|
THE philosopher who first perceived and announced the fact that all the physical doings of man consist simply in changing the places of things made a very profound generalization, and one that is worthy of more serious consideration than it has received.
All our handicraft, however great may be the skill employed, amounts to no more than this. The miner moves the ore and the fuel from their subterranean resting-places, then they are moved into the furnace, and by another moving of combustibles the working of the furnace is started; then the metals are moved to the foundries and forges, then under hammers, or squeezers, or into melting-pots, and thence to molds. The workman shapes the bars, or plates, or castings, by removing a part of their substance, and by more and more movings of material produces the engine, which does its work when fuel and water are moved into its fireplace and boiler.
The statue is within the rough block of marble; the sculptor merely removes the outer portions, and thereby renders his artistic conception visible to his fellow-men.
The agriculturist merely moves the soil in order that it may receive the seed, which he then moves into it, and, when the growth is completed, he moves the result, and thereby makes his harvest.
The same may be said of every other operation. Man alters the position of physical things in such wise that the forces of Nature shall operate upon them and produce the changes or other results that he requires.
My reasons for this introductory digression will be easily understood, as this view of the doings of man and the doings of Nature displays fundamentally the business of human education, so far as the physical proceedings and physical welfare of mankind are concerned.
It clearly points out two well-marked natural divisions of such education: education or training in the movements to be made, and education in a knowledge of the consequences of such movements—i. e., in a knowledge of the forces of Nature which actually do the work when man has suitably arranged the materials.
The education ordinarily given to apprentices in the workshop, or the field, or the studio—or, as relating to my present subject, the kitchen—is the first of these; the second, and equally necessary, being simply and purely the teaching of physical science as applied to the arts.
I can not proceed any further without a protest against a very general (so far as this country is concerned) misuse of a now very popular term—a misuse that is rather surprising, seeing that it is accepted by scholars who have devoted the best of their intellectual efforts to the study of words. I refer to the word technical as applied in the designation "technical education."
So long as our workshops are separated from our science-schools and colleges, it is most desirable, in order to avoid continual circumlocution, to have terms that shall properly distinguish between the work of the two, and admit of definite and consistent use. The two words are ready at hand, and, although of Greek origin, have become by analogous usage plain, simple English. I mean the words technical and technological.
The Greek noun techne signifies an art, trade, or profession, and our established usage of this root is in accordance with this signification. Therefore "technical education" is a suitable and proper designation of the training which is given to apprentices, etc., in the strictly technical details of their trades, arts, or professions. When we require a name for the science or the philosophy of anything, we obtain it by using the Greek root logos, and appending it in English form to the Greek name of the general subject, as geology, the science of the earth; anthropology, the science of man; biology, the science of life, etc.
Why not, then, follow this general usage, and adopt "technology" as the science of trades, arts, or professions, and thereby obtain consistent and convenient terms to designate the two divisions of eduction—technical education, that given in the workshop, etc.; and technological education, that which should he given as supplementary to all such technical education?
In accordance with this, the papers I am here commencing will be a contribution to the technology of cookery, or to the technological education of cooks, whose technical education is quite beyond my reach.
The kitchen is a chemical laboratory, in which are conducted a number of chemical processes, by which our food is converted from its crude state to a condition more suitable for digestion and nutrition, and made more agreeable to the palate.
It is the rationale or ology of these processes that I shall endeavor to explain; but at the outset it is only fair to say that in many instances I shall not succeed in doing this satisfactorily, as there still remain some kitchen mysteries that have not yet come within the firm grasp of science. The whole story of the chemical differences between a roast, a boiled, and a raw leg of mutton, has not yet been told. You and I, gentle reader, aided by no other apparatus than a knife and fork, can easily detect the difference between a cut out of the saddle of a three-year-old Southdown and one from a ten-months old meadow-fed Leicester; but the chemist in his laboratory, with all his re-agents, test-tubes, beakers, combustion-tubes, potash-bulbs, etc., etc., and his balance turning to one-thousandth of a grain, could not physically demonstrate the sources of these differences of flavor.
Still, I hope to show that modern chemistry can throw into the kitchen a great deal of light that shall not merely help the cook in doing his or her work more efficiently, but shall elevate both the work and the worker, and render the kitchen far more interesting to all intelligent people who have an appetite for knowledge, as well as for food, than it can be while the cook is groping in rule-of-thumb darkness—is merely a technical operator unenlightened by technological intelligence.
In the course of these papers I shall draw largely on the practical and philosophical work of that remarkable man, Benjamin Thompson, the Massachusetts prentice-boy and schoolmaster; afterward the British soldier and diplomatist, Colonel Sir Benjamin Thompson; then colonel of horse and general aide-de-camp of the Elector Charles Theodore, of Bavaria; then major-general of cavalry, Privy Councilor of State, and head of War Department of Bavaria; then Count Rumford of the Holy Roman Empire, and order of the White Eagle; then Military Dictator of Bavaria, with full governing powers during the absence of the Elector; then a private resident in Brompton Road, and founder of the Royal Institution in Albemarle Street; then a Parisian citoyen, the husband of the "Goddess of Reason," the widow of Lavoisier; but above all a practical and scientific cook, whose exploits in economic cookery are still but very imperfectly appreciated, though he himself evidently regarded them as the most important of all his varied achievements.
His faith in cookery is well expressed in the following, where he is speaking of his experiments in feeding the Bavarian army and the poor of Munich. He says: "I constantly found that the richness or quality of a soup depended more upon the proper choice of the ingredients, and a proper management of the fire in the combination of these ingredients, than upon the quantity of solid nutritious matter employed; much more upon the art and skill of the cook than upon the sums laid out in the market."
A great many fallacies are continually perpetrated, not only by ignorant people, but even by eminent chemists and physiologists, by inattention to what is indicated in this passage. In many chemical and physiological works may be found elaborately minute tables of the chemical composition of certain articles of food, and with these the assumption (either directly stated, or implied, as a matter of course) that such tables represent the practical nutritive value of the food. The illusory character of such assumption is easily understood. In the first place, the analysis is usually that of the article of food in its raw state, and thus all the chemical changes involved in the process of cookery are ignored.
Secondly, the difficulty or facility of assimilation is too often unheeded. This depends both upon the original condition of the food and the changes which the cookery has produced—changes which may double its nutritive value without effecting more than a small percentage of alteration in its chemical composition, as revealed by laboratory analysis.
In the recent discussion on whole-meal bread, for example, chemical analyses of the bran, etc., are quoted, and it is commonly assumed that, if these can be shown to contain more of the theoretical bone making or brain-making elements, they are, therefore, in reference to these requirements, more nutritious than the fine flour. But, before we are justified in asserting this, it must be made clear that these ordinarily rejected portions of the grain are as easily digested and assimilated as the finer inner flour.
I think I shall be able to show that the practical failure of this whole-meal bread movement (which is not a novelty, but only a revival) is mainly due to the disregard of the cookery question; that whole-meal prepared as bread by simple baking is less nutritious than fine flour similarly prepared; but that whole-meal otherwise prepared may be, and has been, made more nutritious than fine white bread.
Count Rumford supplies us with important data toward the solution of this difficulty.
Another preliminary example. A pound of bread or biscuit contains more solid nutritive matter than a pound of beefsteak, but does not, when eaten by ordinary mortals, do so much nutritive work. Why is this?
It is a matter of preparation—not exactly what is called cooking, but equivalent to what cooking should be. It is the preparation which has converted the grass-food of the ox into another kind of food which we can assimilate very easily.
The fact that we use the digestive and nutrient apparatus of sheep, oxen, etc., for the preparation of our food is merely a transitory barbarism, to be ultimately superseded when my present subject is sufficiently understood and applied to enable us to prepare the constituents of the vegetable kingdom in such a manner that they shall be as easily assimilated as the prepared grass which we call beef and mutton, and which we now use only on account of our ignorance of "The Chemistry of Cooking."
As this is one of the most rudimentary of the operations of cookery, and the most frequently performed, it naturally takes a first place in treating the subject.
"Water is boiled in the kitchen for two distinct purposes: 1. For the cooking of itself; 2. For the cooking of other things. A dissertation on the difference between raw water and cooked water may appear pedantic, but, as I shall presently show, it is considerable, very practical, and important.
The best way to study any physical subject is to examine it experimentally, but this is not always possible with every-day means. In this case, however, there is no difficulty.
Take a thin glass vessel, such as a flask, or, better, one of the "beakers," or thin, tumbler-shaped vessels, so largely used in chemical laboratories; partially fill it with ordinary household water, and then place it over the flame of a spirit-lamp, or Bunsen's, or other smokeless gas-burner. Carefully watch the result, and the following will be observed: First of all little bubbles will be formed, adhering to the sides of the glass, but ultimately rising to the surface, and there becoming dissipated by diffusion in the air.
This is not boiling, as may be proved by trying the temperature with the finger. What, then, is it?
It is the yielding back of the atmospheric gases which the water has dissolved or condensed within itself. These bubbles have been collected and by analysis proved to consist of oxygen, nitrogen, and carbonic acid, obtained from the air; but in the water they exist by no means in the same proportions as originally in the air, nor in constant proportions in different samples of water. I need not here go into the quantitative details of these proportions, nor the reasons of their variation, though they are very interesting subjects.
Proceeding with our investigation, we shall find that the bubbles continue to form and rise until the water becomes too hot for the finger to bear immersion. At about this stage something else begins to occur. Much larger bubbles, or rather blisters, are now formed on the bottom of the vessel, immediately over the flame, and they continually collapse into apparent nothingness. Even at this stage a thermometer immersed in the water will show that the boiling-point is not reached. As the temperature rises, these blisters rise higher and higher, become more and more nearly spherical, finally quite so, then detach themselves and rise toward the surface; but the first that make this venture perish in the attempt—they gradually collapse as they rise,-and vanish before reaching the surface. The thermometer now shows that the boiling-point is nearly reached, but not quite. Presently the bubbles rise completely to the surface and break there. Now the water is boiling, and the thermometer stands at 212º Fahr. or 100 Cent.
With the aid of suitable apparatus it can be shown that the atmospheric gases above named continue to be given off along with the steam for a considerable time after the boiling has commenced; the complete removal of their last traces being a very difficult, if not an impossible, physical problem.
After a moderate period of boiling, however, we may practically regard the water as free from these gases. In this condition I venture to call it cooked water. Our experiment so far indicates one of the differences between cooked and raw water. The cooked water has been deprived of the atmospheric gases that the raw water contained. By cooling some of the cooked water and tasting it the difference of flavor is very perceptible; by no means improved, though it is quite possible to acquire a preference for this flat, tasteless liquid.
If a fish be placed in such cooked water it swims for a while with its mouth at the surface of the water, for just there is a film that is reacquiring its charge of oxygen, etc., by absorbing it from the air; but this film is so thin and so poorly charged, that after a short struggle the fish dies for lack of oxygen in its blood, drowned as truly and completely as a living, breathing animal when immersed in any kind of water.
Spring and river water that have passed through or over considerable distances in calcareous districts suffer another change in boiling. The origin and nature of this change may be shown by another experiment as follows: Buy a pennyworth of lime-water from a druggist, and procure a small glass tube of about quill-size, or the stem of a fresh tobacco-pipe may be used. Half fill a small wine-glass with the lime-water, and blow through it by means of the tube of the tobacco-pipe. Presently it will become turbid. Continue the blowing, and the turbidity will increase up to a certain degree of milkiness. Go on blowing with "commendable perseverance," and an inversion of effect will follow: the turbidity diminishes, and at last the water becomes clear again.
The chemistry of this is simple enough. From the lungs a mixture of nitrogen, oxygen, and carbonic acid is exhaled. The carbonic acid combines with the soluble lime and forms a carbonate of lime which is insoluble in mere water. But this carbonate of lime is to a certain extent soluble in water saturated with carbonic acid, and such saturation is effected by the continuation of blowing.
Now take some of the lime-water that has been thus treated, place it in a clean glass flask, and boil it. After a short time the flask will be found incrusted with a thin film of something. This is the carbonate of lime, which has been thrown down again by the action of boiling in drawing off its solvent, the carbonic acid. This crust will effervesce if a little acid is added to it.
In this manner our tea-kettles, engine-boilers, etc., become incrusted when fed with calcareous waters, and most waters are calcareous; those supplied to London, which is surrounded by chalk, are largely so. Thus the boiling or cooking of such water effects a removal of its mineral impurities more or less completely. Other waters contain such mineral matter as salts of sodium and potassium. These are not removable by mere boiling.
Usually we have no very strong motive for removing either these or the dissolved carbonate of lime, or the atmospheric gases from water, but there is another class of impurities of serious importance. These are the organic matters dissolved in all water that has run over land covered with vegetable growth, or, more especially, which has received contributions from sewers or any other form of house-drainage. Such water supplies nutriment to those microscopic abominations, the mirococci, bacilli, bacteria, etc., which are now shown to be connected with blood-poisoning—possibly do the whole of the poisoning business. These little pests are harmless, and probably nutritious, when cooked, but in their raw and wriggling state are horribly prolific in the blood of people who are in certain states of what is called "receptivity." They (the bacteria, etc.) appear to be poisoned or somehow killed off by the digestive secretions of the blood of some people, and nourished luxuriantly in the blood of others. As nobody can be quite sure to which class he belongs, or may presently belong, or whether the water supplied to his household is free from blood-poisoning organisms, cooked water is a safer beverage than raw water.
The requirement for this simple operation of cooking increases with the density of our population, which on reaching a certain degree renders the pollution of all water obtained from the ordinary sources almost inevitable.
Reflecting on this subject, I have been struck with a curious fact that has hitherto escaped notice, viz., that, in the country which over all others combines a very large population with a very small allowance of cleanliness, the ordinary drink of the people is boiled water flavored by an infusion of leaves. These people, the Chinese, seem, in fact, to have been the inventors of boiled-water beverages. Judging from travelers' accounts of the state of the rivers, rivulets, and general drainage and irrigation arrangements of China, its population could scarcely have reached its present density if Chinamen were drinkers of raw instead of cooked water.
Next to the boiling of water for its own sake, as treated in my last, comes the boiling of water as a medium for the cooking of other things. Here, at the outset, I have to correct an error of language which, as too often happens, leads by continual suggestion to false ideas. When we speak of "boiled beef," "boiled mutton," "boiled eggs," "boiled potatoes," we talk nonsense; we are not merely using an elliptical expression, as when we say "the kettle boils," which we all understand to mean the contents of the kettle, but we are expounding a false theory of what has happened to the beef, etc.—as false as though we should describe the material of the kettle that has held boiling water as boiled copper or boiled iron. No boiling of the food takes place in any such cases as the above-named—it is merely heated by immersion in boiling water; the changes that actually take place in the food are essentially different from those of ebullition. Even the water contained in the meat is not boiled in ordinary cases, as its boiling-point is higher than that of the surrounding water, owing to the salts it holds in solution.
Thus, as a matter of chemical fact, a "boiled leg of mutton" is one that has been cooked, but not boiled; while a roasted leg of mutton is one that has been partially boiled. Much of the constituent water of flesh is boiled out, fairly driven away as vapor during roasting or baking, and the fat on its surface is also boiled, and, more or less, dissociated into its chemical elements, carbon and water, as shown by the browning, due to the separated carbon.
As I shall presently show, this verbal explanation is no mere verbal quibble, but it involves important practical applications. An enormous waste of precious fuel is perpetrated every day, throughout the whole length and breadth of Britain and other countries where English cookery prevails, on account of the almost universal ignorance of the philosophy of the so-called boiling of food.
When it is once fairly understood that the meat is not to be boiled, but is merely to be warmed by immersion in water raised to a maximum temperature of 212º, and when it is further understood that water can not (under ordinary atmospheric pressure) be raised to a higher temperature than 212º by any amount of violent boiling, the popular distinction between "simmering" and boiling, which is so obstinately maintained as a kitchen superstition, is demolished.
The experiment described in my last showed that immediately the bubbles of steam reach the surface of the water and break there—that is, when simmering commences—the thermometer reaches the boiling point, and that however violently the boiling may afterward occur, the thermometer rises no higher. Therefore, as a medium for heating the substance to be cooked, simmering water is just as effective as "walloping" water. There are exceptional operations of cookery, to be described hereafter, wherein useful mechanical work is done by violent boiling; but in all ordinary cookery, simmering is just as effective. The heat that is applied to do more than the smallest degree of simmering is simply wasted in converting water into useless steam. The amount of such waste may be easily estimated. To raise a given quantity of water from the freezing to the boiling point demands an amount of heat represented by 180º in Fahrenheit's thermometer, or 100º Centigrade. To convert this into steam, 990º Fahr. or 500º Cent, is necessary—just five and a half times as much.
On a properly-constructed hot-plate or sand-bath, a dozen saucepans may be kept at the true cooking temperature, with an expenditure of fuel commonly employed in England to "boil" one saucepan. In the great majority of so-called boiling operations, even simmering is unnecessary. Not only is a "boiled leg of mutton" not itself boiled, but even the water in which it is cooked should not be kept boiling, as we shall presently see.
In order to illustrate some of the changes which take place in the cooking of animal food, I will first take the simple case of cooking an egg by means of hot water. These changes are in this case easily visible and very simple, although the egg itself contains all the materials of a complete animal. Bones, muscles, viscera, brain, nerves, and feathers of the chicken all—are produced within the shell, nothing being added, and little or nothing taken away.
When we open a raw egg, we find, enveloped in a stoutish membrane, a quantity of glairy, slimy, viscous, colorless fluid, which, as everybody now knows, is called albumen, a Latin translation of its common name, "the white." Within the white of the egg is the yolk, largely composed of that same albumen, but with other constituents added—notably a peculiar oil. At present I will only consider the changes which cookery effects on the main constituent of the egg, merely adding that this same albumen is one of the most important, if not the one most important, material of animal food, and is represented by a corresponding nutritious constituent in vegetables.
We all know that when an egg has been immersed during a few minutes in boiling water, the colorless, slimy liquid is converted into the white solid to which it owes its name. This coagulation of albumen is one of the most decided and best understood changes effected by cookery, and therefore demands especial study.
Place some fresh, raw white of egg in a test-tube, or other suitable glass vessel, and in the midst of it immerse the bulb of a thermometer. (Cylindrical thermometers, with the degrees marked on the glass stem, are made for such laboratory purposes.) Place the tube containing the albumen in a vessel of water, and gradually heat this. When the albumen attains a temperature of about 134º Fahr., white fibers will begin to appear within it; these will increase until about 160º is attained, when the whole mass will become white and nearly opaque. It is now coagulated, and may be called solid. Now examine some of the result, and you will find that the albumen thus only just coagulated is a tender, delicate, jelly-like substance, having every appearance to sight, touch, and taste of being easily digestible. This is the case.
Having settled these points, proceed with the experiment by heating the remainder of the albumen (or a new sample) up to 212º, and keeping it for a while at this temperature. It will dry, shrink, and become horny. If the heat is carried a little further, it becomes converted into a substance which is so hard and tough that a valuable cement is obtained by simply smearing the edges of the article to be cemented with white of egg, and then heating it to a little above 212º.
This simple experiment teaches a great deal of what is but little known concerning the philosophy of cookery. It shows in the first place that, so far as the coagulation of the albumen is concerned, the cooking temperature is not 212º, or that of boiling water, but 160º, i. e., 52º below it. Everybody knows the difference between a tender, juicy steak, rounded or plumped-out in the middle, and a tough, leathery abomination, that has been so cooked as to shrivel and curl up. The contraction, drying up, and hornifying of the albumen in the test tube represent the albumen of the latter, while the tender, delicate, trembling, semi-solid, that was coagulated at 160º, represents the albumen in the first.
But this is a digression, or rather anticipation, seeing that the grilling of a beefsteak is a problem of profound complexity that we can not solve until we have mastered the rudiments. We have not yet determined how to practically apply the laws of albumen coagulation as discovered by our test-tube experiment to the cooking of a breakfast-egg.—Knowledge.
- In applying heat to glass vessels, thickness is a source of weakness or liability to fracture, on account of the unequal expansion of the two sides, due to inequality of temperature, which, of course, increases with the thickness of the glass. Besides this, the thickness increases the leverage of the breaking strain.
- "Egg-cement," made by thickening white of egg with finely-powdered quicklime, has long been used for mending alabaster, marble, etc. For joining fragments of fossils and mineralogical specimens, it will be found very useful. White of egg alone may be used, if carefully heated afterward.