Popular Science Monthly/Volume 24/November 1883/The Chemistry of Cookery VI
|THE CHEMISTRY OF COOKERY.|
A CORRESPONDENT of Manchester asks me which is the most nutritious, a slice of English beef in its own gravy, or the browned morsel as served in an Italian restaurant with the burnt-sugar addition to the gravy? This is a very fair question, and not difficult to answer. If both are equally cooked, neither over-done nor under-done, they must contain, weight for weight, exactly the same constituents in equally digestible form, so far as chemical composition is concerned. Whether they will actually be digested with equal facility and assimilated with equal completeness depends upon something else not measurable by chemical analysis, viz., the relish with which they are respectively eaten. To some persons the undisguised fleshiness of the English slice, especially if under-done, is very repugnant. To these the corresponding morsel, cooked according to Francatelli rather than Mrs. Beeton, would be more nutritious. To the carnivorous John Bull, who regards such dishes as "nasty French messes" of questionable composition, the slice of unmistakable ox-flesh from a visible joint would obtain all the advantages of appreciative mastication and that sympathy between the brain and the stomach which is so powerful that, when discordantly exerted, may produce the effects that are recorded in the case of the sporting traveler who was invited by a Red Indian chief to a "dog-fight," and ate with relish the savory dishes at what he supposed to be a preliminary banquet. Digestion was tranquilly and healthfully proceeding, under the soothing influence of the calumet, when he asked the chief when the fight would commence. On being told that it was over, and that in the final ragoût he had praised so highly the last puppy-dog possessed by the tribe had been cooked in his honor, the normal course of digestion of the honored guest was completely reversed.
Reverting to the fat used in frying, and the necessity of its purification, I may illustrate the principle on which it should be conducted by describing the method adopted in the refining of mineral oils, such as petroleum or the paraffin distillates of bituminous shales. These are dark, tarry liquids of treacle-like consistency, with a strong and offensive odor. Nevertheless, they are, at but little cost, converted into the "crystal-oil" used for lamps, and that beautiful pearly substance, the solid, translucent paraffin now so largely used in the manufacture of candles. Besides these, we obtain from the same dirty source an intermediate substance, the well-known "vaseline" now becoming the basis of most of the ointments of the pharmacopœia. This purification is effected by agitation with sulphuric acid, which partly carbonizes and partly combines with the impurities, and separates them in the form of a foul and acrid black mess, known technically as "acid tar." When I was engaged in the distillation of cannel and shale in Flintshire, this acid tar was a terrible bugbear. It found its way mysteriously into the Alyn River, and poisoned the trout; but now, if I am correctly informed, the Scotch manufacturers have turned it to profitable account.
Animal fat and vegetable oils are similarly purified. Very objectionable refuse fat of various kinds is thus made into tallow, or material for the soap-maker, and grease for lubricating machinery. Unsavory stories have been told about the manufacture of butter from Thames mud or the nodules of fat that are gathered therefrom by the mud-larks, but they are all false. It may be possible to purify fatty matter from the foulest of admixtures, and do this so completely as to produce a soft, tasteless fat, i.e., a butter substitute, but such a curiosity would cost more than half a crown per pound, and therefore the market is safe, especially as the degree of purification required for soap-making and machinery-grease costs but little, and the demand for such fat is very great.
These methods of purification are not available in the kitchen, as oil of vitriol is a vicious compound. During the siege of Paris some of the Academicians devoted themselves very earnestly to the subject of the purification of fat in order to produce what they termed "siege-butter" from the refuse of slaughter-houses, etc., and edible salad oils from crude colza oil, the rancid fish oils used by the leather-dresser, etc. Those who are specially interested in the subject may find some curious papers in the "Comptes Rendus" of that period. In vol. lxxi, page 36, M. Boillot describes his method of mixing kitchen-stuff and other refuse fat with lime-water, agitating the mixture when heated, and then neutralizing with an acid. The product thus obtained is described as admirably adapted for culinary operations, and the method is applicable to the purpose here under consideration.
Further on in the same volume is a "Note on Suets and Alimentary Fats" by M. Dubrunfaut, who tells us that the most tainted of alimentary fats and rancid oils may be deprived of their bad odors by "appropriate frying." His method is to raise the temperature of the fat to 140° to 150° Centigrade (284° to 302° Fahr.) in a frying-pan; then cautiously sprinkle upon it small quantities of water. The steam carries off the volatile fatty acids producing the rancidity in such as fish-oils, and also the neutral offensive fatty matters that are decomposed by the heat. In another paper by M. Fua this method is applied to the removal of cellular tissue of crude fats from slaughter-houses. It is really nothing more than the old farm-house proceeding of "rendering" lard, by frying the membranous fat until the membranous matter is browned and aggregated into small nodules, which constitute the "scratchings"—a delicacy greatly relished by our British plowboys at pig-killing time, but rather too rich in pork-fat to supply a suitable meal for people of sedentary vocations.
The action of heat thus applied and long continued is similar to that of the strong sulphuric acid. The impurities of the fat are organic matters more easily decomposable than the fat itself, or, otherwise stated, they are dissociated into carbon and water at about 300° Fahr., which is a lower temperature than that required for the dissociation of the pure oil or fat (see No. 13 of this series). By maintaining this temperature, these compounds become first caramelized, then carbonized nearly to blackness, and all their powers of offensiveness vanish, as such offense is due to slow decomposition of the original organic compounds, which now exist no longer, and the remaining caramel or carbon cinders being quite inoffensive or no further decomposable by atmospheric agency.
In the more violent factory process of purification by sulphuric acid the similar action which occurs is due to the powerful affinity of this acid for water; this may be strikingly shown by adding to thickor pounded sugar about its own bulk of oil of vitriol, when a marvelous commotion occurs, and a magnified black cinder is produced by the separation of the water from the sugar.
The following simple practical formula may be reduced from these data. When a considerable quantity of much-used frying fat is accumulated, heat it to about 300° Fahr., as indicated by the crackling of water when sprinkled on it, or, better still, by a properly constructed kitchen thermometer graduated to about 400° Fahr. Then pour the melted fat on hot water. This must be done carefully, as a large quantity of fat at 400° poured upon a small quantity of boiling water will illustrate the fact that water when suddenly heated is an explosive compound. The quantity of water should exceed that of the fat, and the pouring be done gradually. Then agitate the fat and water together, and, if the operator is sufficiently skillful and intelligent, the purification may be carried further by carefully boiling the water under the fat, and allowing its steam to pass through; but this is a little dangerous, on account of the possibility of what the practical chemist calls "bumping," or the sudden formation of a big bubble of steam that would kick a good deal of the superabundant fat into the fire.
Whether this supplementary boiling is carried out or not, the fat and the water should be left together to cool gradually, when a dark layer of carbonized impurities will be found resting on the surface of the water, and adhering to the bottom of the cake of fat. This may be peeled off and put into the waste grease-pot, to be further refined with the next operation. Ultimately the worst of it will sink to the bottom of the water. Then it is of no further value, and will be found to be a mere cinder.
Regarding the fat used in frying as a medium for conveying heat, freedom from any special flavor of its own is a primary desideratum. Olive-oil of the best quality is almost absolutely tasteless, and, having as high a boiling-point as animal fats, it is the best of all frying media. In this country there is a prejudice against the use of such oil. I have noticed at some of those humble but most useful establishments where poor people are supplied with penny or twopenny portions of good fish, better cooked than in the majority of "eligible villa residences," that in the front is an inscription stating that "only the best beef-dripping is used in this establishment." This means a repudiation of oil. Such oil as has been supplied for fish-frying may well be repudiated.
On my first visit to arctic Norway I arrived before the garnering and exportation of the spring cod harvest was completed. The packet stopped at a score or so of stations on the Lofodens and the mainland. Foggy weather was no impediment, as an experienced pilot free from catarrh could steer direct to the harbor by "following his nose." Huge caldrons stood by the shore in which were stewing the last batches of the livers of cod-fish caught a month before and exposed in the mean time to the continuous arctic sunshine. Their condition must be imagined, as I abstain from description of details. The business then proceeding was the extraction of the oil from these livers. It is, of course, "cod-liver oil," but is known commercially as "fish-oil," or "cod-oil." That which is sold by our druggists as cod-liver oil is described in Norway as "medicine-oil," and though prepared from the same raw material, is extracted in a different manner. Only fresh livers are used for this, and the best quality, the "cold-drawn" oil, is obtained by pressing the livers without stewing. Those who are unfortunately familiar with this carefully prepared, highly refined product, know that the fishy flavor clings to it so pertinaciously that all attempts to completely remove it without decomposing the oil have failed. This being the case, it is easily understood that the fish-oil stewed so crudely out of the putrid or semi-putrid livers must be nauseous indeed. I am told that it has nevertheless been used by some of the fish-fryers, and I know that refuse "Gallipoli" (olive-oil of the worst quality) is sold for this purpose. The oil obtained in the course of salting sardines, herrings, etc., has also been used.
Such being the case, it is not surprising that the use of oil for frying should, like the oil itself, be in bad odor.
I dwell upon this because we are probably on what, if a fine writer, I should call the "eve of a great revolution" in respect to frying media.
Two new materials, pure, tasteless, and so cheap as to be capable of pushing pig-fat (lard) out of the market, have recently been introduced. These are cotton-seed oil and poppy-seed oil. The first has been for some time in the market offered for sale under various fictitious names, which I will not reveal, as I refuse to become a medium for the advertisement of anything—however good in itself—that is sold under false pretenses. If the lamp of Knowledge, more fortunate than that of Diogenes, should light upon some honest men who will retail cotton-seed oil as cotton-seed oil, I shall gladly (with the editor's permission) do a little straightforward touting for them, as they will be public benefactors, greatly aiding the present movement for the extension of the use of fish-food.
As every bale of cotton yields half a ton of seed, and every ton of seed may be made to yield twenty-eight to thirty-two pounds of crude oil, the available quantity is very great. At present only a small quantity is made, the surplus seed being used as manure. Its fertilizing value would not be diminished by removing the oil, which is only a hydro-carbon, i. e., material supplied by air and water. All the fertilizing constituents of the seed are left behind in the oil-cake from which the oil has been pressed.
Hitherto cotton-seed oil has fallen among thieves. It is used as an adulterant of olive-oil; sardines and pilchards are packed in it. The sardine trade has declined lately, some say from deficient supplies of the fish. I suspect that there has been a decline in the demand, due to the substitution of this oil for that of the olive. Many people who formerly enjoyed sardines no longer care for them, and they do not know why. The substitution of cotton-seed oil explains this in most cases. It is not rancid, has no decided flavor, but still is unpleasant when eaten raw, as with salads or sardines. It has a flat, cold character, and an after-taste that is faintly suggestive of castor-oil; but faint as it is, it interferes with the demand for a purely luxurious article of food. This delicate defect is quite inappreciable in the results of its use as a frying medium. The very best lard or ordinary kitchen butter, eaten cold, has more of objectionable flavor than refined cotton-seed oil.
I have not tasted poppy-seed oil, but am told that it is similar to that from the cotton-seed. As regards the quantities available, some idea may be formed by plucking a ripe head from a garden poppy and shaking out the little round seeds through the windows on the top. Those who have not tried this will be astonished at the numbers produced by each flower. As poppies are largely cultivated for the production of opium, and the yield of the drug itself by each plant is very small, the supplies of oil may be considerable; 571,542 cwt. of seeds were exported from India last year, of which 346,031 cwt. went to France.
Palm-oil, though at present practically unknown in the kitchen, may easily become an esteemed material for the frying-kettle (I say "kettle," as the ordinary English frying-pan is only fit for the cooking of such things as barley bannocks, pancakes, fladbrod, or oatcakes). At present, the familiar uses of palm-oil in candle-making and for railway grease will cause my suggestion to shock the nerves of many delicate people, but these should remember that before palm-oil was imported at all, the material from which candles and soap were made, and by which cart-wheels and heavy machinery were greased, was tallow i. e., the fat of mutton and beef. The reason why our grandmothers did not use candles when short of dripping or suet was that the mutton-fat constituting the candle was impure; so are the yellow candles and yellow grease in the axle-boxes of the railway carriages. This vegetable fat is quite as inoffensive in itself, quite as wholesome, and—sentimentally regarded—less objectionable, than the fat obtained from the carcass of a slaughtered animal.
When common sense and true sentiment supplant mere unreasoning prejudice, vegetable oils and vegetable fats will largely supplant those of animal origin in every element of our dietary. We are but just beginning to understand them. Chevreul, who was the first to teach us the chemistry of fats, is still living, and we are only learning, how to make butter (not "inferior Dorset," but "choice Normandy") without the aid of dairy produce. There is, therefore, good reason for anticipating that the inexhaustible supplies of oil obtainable from the vegetable world—especially from tropical vegetation—will ere long be freely available for kitchen uses, and the now popular product of the Chicago hog factories will be altogether banished therefrom, and used only for greasing cart-wheels and other machinery.
As a practical conclusion of this part of my subject, I will quote from this month's number of "The Oil Trade Review" the current wholesale prices of some of the oils possibly available for frying purposes. Olive-oil, from £43 to £90 per ton of 252 gallons; Cod-oil, £36 per ton; Sardine or train (i. e., the oil that drains from pilchards, herrings, sardines, etc., when salted), £27 10s. to £28 per ton. Cocoa-nut, from £35 to £38 per ton of 20 cwt. (This, in the case of oil, is nearly the same as the measured ton.) Palm, from £38 to £40 10s. per ton; Palm-nut or copra, £31 10s. per ton; Refined cotton-seed, £30 10s. to £31 per ton; Lard, £53 to £55 per ton. The above are the extreme ranges of each class. I have not copied the technical names and prices of the intermediate varieties. One penny per pound is £9 6s. 8d. per ton, or, in round numbers, £1 per ton may be reckoned as one ninth of a penny per pound. Thus the present price of best refined cotton-seed oil is 3½d. per pound; of cocoanut-oil, 3¾d.; palm-oil, from 3½d. to 4½d., while lard costs 6d. per pound wholesale—usually 7d.
I should add, in reference to the seed-oils, that there is a possible objection to their use as frying media. Oils extracted from seeds contain more or less of linoleine (so named from its abundance in linseed-oil), which, when exposed to the air, combines with oxygen, swells and dries. If the oil from cotton-seed or poppy-seed contains too much of this, it will thicken inconveniently when kept for a length of time exposed to the air. Palm-oil is practically free from it, but I am doubtful respecting palm-nut-oil, as most of the nut-oils are "driers."—Knowledge.