We all know that there is a considerable difference between raw fat and cooked fat; but what is the rationale of this difference? Is it anything beyond the obvious fusion or semi-fusion of the solid?

These are very natural and simple questions, but in no work on chemistry or technology can I find any answer to them, or even any attempt at an answer. I will therefore do the best I can towards solving the problem in my own way.

All the cookable and eatable fats fall into the class of ‘fixed oils,’ so named by chemists to distinguish them from the ‘volatile oils,’ otherwise described as ‘essential oils.’ The distinction between these two classes is simple enough. The volatile oils (mostly of vegetable origin) may be distilled or simply evaporated away like water or alcohol, and leave no residue. The fixed oils similarly treated are dissociated more or less completely. This has been already explained in Chapter VII.

Otherwise expressed, the boiling point of the volatile oils is below their dissociation point. The fixed oils are those which are dissociated at a temperature below their boiling point.

My object in thus expressing this difference will be understood upon a little reflection. The volatile oils, when heated, being distilled without change are uncookable; while the fixed oils if similarly heated suffer various degrees of change as their temperature is raised, and may be completely decomposed by steady application of heat in a closed vessel without the aid of any other chemical agent than the heat itself. This ‘destructive distillation’ converts them into solid carbon and hydro-carbon gases, somewhat similar to those we obtain by the destructive distillation of coal.

If we watch the changes occurring as the heat advances to this complete dissociation point we may observe a minor or partial dissociation proceeding gradually onward, resembling that which I have already described as occurring when sugar is similarly treated (Chapter VII. page 87).

But in ordinary cooking we do not go so far as to carbonise the fat itself, though we do brown or partially carbonise the membrane which envelopes the fat. What then is the nature of this minor dissociation, if such occurs?

Before giving my answer to this question I must explain the chemical constitution of fat. It is a compound of a very weak base with very weak acids. The basic substance is glycerine, the acids (not sour at all, but so named because they combine with bases as the actually sour acids do) are stearic acid, palmitic acid, oleic acid, &c., and bear the general name of ‘fatty acids.’ They are solid or liquid, according to temperature. When solid they are pearly crystalline substances, when fused they are oily liquids.

To simplify, I will take one of these as a type, and that the one which is the chief constituent of animal fats, viz. stearic acid. I have a lump of it before me. Newly broken through, it might at a distance be mistaken for a piece of Carrara marble. It is granular, like the marble, but not so hard, and, when rubbed with the hand, differs from the marble in betraying its origin by a small degree of unctuousness, but it can scarcely be described as greasy.

I find by experiment that this may be mixed with glycerine without combination taking place, that when heated with glycerine just to its fusing point, and the two are agitated together, the combination is by no means complete. Instead of obtaining a soft, smooth fat, I obtain a granular fat small stearic crystals with glycerine amongst them. It is a mixture of stearic acid and glycerine, not a chemical compound; it is stearic acid and glycerine, but not a stearate of glycerine or glycerine stearate.

A similar separation is what I suppose to occur in the cooking of animal fat. I find that mutton-fat, beef-fat, or other fat when raw is perfectly smooth, as tested by rubbing a small quantity, free from membrane, between the finger and thumb, or by the still more delicate test of rubbing it between the tip of the tongue and the palate. But dripping, whether of beef, or mutton, or poultry, is granular, as anybody who has ever eaten bread and dripping knows well enough, and the manufacturers of ‘butterine,’ or ‘bosch,’ know too well, the destruction or prevention of this granulation being one of the difficulties of their art.

My theory of the cookery of fat is simply that heat, when continued long enough, or raised sufficiently high, effects an incipient dissociation of the fatty acids from the glycerine, and thus assists the digestive organs by presenting the base and the acids in a condition better fitted (or advanced by one stage) for the new combinations demanded by assimilation. Some physiologists have lately asserted that the fat of our food is not assimilated at all—not laid down again as fat, but is used directly as fuel for the maintenance of animal heat.

If this is correct, the advantage of the preliminary dissociation is more decided, for the combustible portion of the fat is its fatty acids; the glycerine is an impediment to combustion, so much so that the modern candle-maker removes it, and thereby greatly improves the combustibility of his candles.

It may be that the glycerine of the fat we eat is assimilated like sugar, while the fatty acids act directly as fuel. This view may reconcile some of the conflicting facts (such as the existence of fat in the carnivora) that stand in the way of the theory of the uses of fat food above referred to, according to which fat is not fattening, and those who would ‘Bant’ should eat fat freely to maintain animal heat, while very abstemious in the consumption of sugar and farinaceous food.

The difference between tallow and dripping is instructive. Their origin is the same; both are melted fats—beef or mutton fats—and both contain the same fatty acids and glycerine, but there is a visible and tangible difference in their molecular condition. Tallow is smooth and homogeneous, dripping decidedly granular.

I attribute this difference to the fact that in rendering tallow, the heat is maintained no longer than is necessary to effect the fusion; while, in the ordinary production of dripping, the fat is exposed in the dripping-pan to a long continuance of heat, besides being highly heated when used in basting. Therefore the dissociation is carried farther in the case of the dripping, and the result becomes sensible.

I have observed that home-rendered lard, that obtained in English farmhouses, where the ‘scratchings’ (i.e. the membranous parts) are frizzled, is more granular than the lard we now obtain in such abundance from Chicago and other wholesale hog regions. I have not witnessed the lard rendering at Chicago, but have little doubt that economy of fuel is practised in conducting it, and therefore less dissociation would be effected than in the domestic retail process.

Some of the early manufacturers of ‘bosch’ purified their fat by the process recommended and practised by the French Academicians MM. Dubrunfaut and Fua (see page 102). I wrote about it in 1871, and consequently received some samples of artificial butter thus made in the Midlands. It was pure fat, perfectly wholesome, but, although coloured to imitate butter, had the granular character of dripping. Since that time great progress has been made in this branch of industry. I have lately tasted samples of pure ‘bosch’ or ‘oleomargarine’ undistinguishable from churned cream or good butter, though offered for sale at 8½d. per lb. in wholesale packages. In the preparation of this the high temperatures of the process of the Academicians are carefully avoided, and the smoothness of pure butter is obtained. I mention this now merely in confirmation of my theory of the rationale of fat cookery, but shall return to this subject of ‘bosch’ or butterine again, as it has considerable intrinsic interest in reference to our food supplies, and should be better understood than it is.

If this theory of fat cookery and the preceding theoretical explanations of the cookery of gelatin and fibrin are correct, a broad practical deduction follows, viz. that in the cookery of fat the full temperature of 212° or even a much higher temperature does no mischief, or may be desirable, while all the other constituents of meat are better cooked at a temperature not exceeding 212°; the albumen especially at a considerably lower temperature.

There is neither coagulation nor dehydration to be feared as regards the fat, unless the heat is raised to that of the dissociation of the fixed oils, which, as already explained, is much above 212°; the change which then takes place in the fat (analogous to that caramelising sugar) is not dehydration properly so called, although the elements of water or hydrogen may be driven off.

Hydration is a combining of water as water, not with the elements of water as elements, and the water of most hydrates becomes dissociated at a temperature a little above the boiling point of water.

My own experiments on gelatin show that hydration occurs when crude gelatin is exposed to the action of water at or below the boiling point, and that dehydration takes place at and above the boiling point, or otherwise stated, the boiling point is the critical temperature where either hydration or dehydration may occur according to the circumstances.

The original membrane immersed in water at 212° becomes hydrated, while hydrated gelatin heated to 212° and exposed to the air is dehydrated. Fat is only dissociated as regards its glycerine, and is cooked thereby.

The dietetic value of milk is obvious enough from the fact that the young of the human species and all the mammalia, whether carnivorous, graminivorous, or herbivorous, are entirely fed upon it during the period of their most rapid growth. This, however, does not justify the practice of describing milk as a model diet and tabulating its composition as that which should represent the composition of food for adults. The fallacy of this is evident from the fact that grass is the model food of the cow, and milk that of the calf. Although the grass contains all the constituents of the milk, their proportions are widely different; besides this the grass contains a very great deal of material that does not exist in milk—silica for example.

The constituents of milk are first water, constituting from 65 to 90 per cent. Nitrogenous matter, consisting of the casein above described and a little albumen. Fat, sugar, and saline substances. The proportions of these vary so greatly in the milk from different animals of the same species, and in that from the same animal at different times that tabular statements of the percentage composition of the milk of different animals are very variable. I have five such tables before me, assembled for the purpose of supplying material for my readers, but they are so contradictory, though all by good chemists, that I am at a loss in making a choice. The following is Dr. Miller’s statement of the mean result of several analyses:

The fat exists in the form of minute globules of oil suspended in the water. The rising of these to the surface forms the cream. When the milk is new it is slightly alkaline, and this assists in the admixture of the oil with the water, forming an emulsion which may be imitated by whipping olive or other similar oil in water. If the water is slightly alkaline the milky-looking emulsion is more easily obtained than in neutral water, still more so than when there is acid in the water.

As milk becomes older lactic acid is formed; at first alkalinity is exchanged for neutrality, and afterwards the milk becomes acid. This assists in the separation of the cream.

Butter is merely the oil globules aggregated by agitation or churning. The condition of the casein has been already described. The sugar of milk or ‘lactine’ is much less sweet than cane sugar.

The cookery of milk is very simple, but by no means unimportant. That there is an appreciable difference between raw and boiled milk may be proved by taking equal quantities of each (the boiled sample having been allowed to cool down), adding them to equal quantities of the same infusion of coffee, then critically tasting the mixtures. The difference is sufficient to have long since established the practice among all skilful cooks of scrupulously using boiled milk for making cafÉ au lait. I have tried a similar experiment on tea, and find that in this case the cold milk is preferable. Why this should be—why boiled milk should be better for coffee and raw milk for tea—I cannot tell. If any of my readers have not done so already, let them try similar experiments with condensed milk, and I have no doubt that the verdict of the majority will be that it is passable with coffee, but very objectionable in tea. This is milk that has been very much cooked.

The chief definable alteration effected by the boiling of milk is the coagulation of the small quantity of albumen which it contains. This rises as it becomes solidified, carrying with it some of the fat globules of the milk, and a little of its sugar and saline constituents, thus forming a skin-like scum on the surface, which may be lifted with a spoon and eaten, as it is perfectly wholesome, and very nutritious.

If all the milk that is poured into London every morning were to flow down a single channel, it would form a respectable little rivulet. An interesting example of the self-adjusting operation of demand and supply is presented by the fact that, without any special legislation or any dictating official, the quantity required should thus flow with so little excess that, in spite of its perishable qualities, little or none is spoiled by souring; and yet at any moment anybody may buy a pennyworth within two or three hundred yards of any part of the great metropolis. There is no record of any single day on which the supply has failed, or even been sensibly deficient.

This is effected by drawing the supplies from a great number of independent sources, which are not likely to be simultaneously disturbed in the same direction. Coupled with this advantage is a serious danger. It has been demonstrated that certain microbia (minute living abominations), which are said to disseminate malignant diseases, may live in milk, feed upon it, increase and multiply therein, and by it be transmitted to human beings with possibly serious and even fatal results.

This general germ theory of disease has been recently questioned by some men whose conclusions demand respect. Dr. B. W. Richardson stoutly opposes it, and in the particular instance of the ‘comma-shaped’ bacillus, so firmly described as the origin of cholera, the refutation is apparently complete.

The alternative hypothesis is that the class of diseases in question are caused by a chemical poison, not necessarily organised as a plant or animal, and therefore not to be found by the microscope.

I speak the more feelingly on this subject, having very recently had painful experience of it. One of my sons went for a holiday to a farm-house in Shropshire, where many happy and health-giving holidays have been spent by all the members of my family. At the end of two or three weeks he was attacked by scarlet fever, and suffered severely. He afterwards learned that the cowboy had been ill, and further inquiry proved that his illness was scarlet fever, though not acknowledged to be such; that he had milked before the scaling of the skin that follows the eruption could have been completed, and it was therefore most probable that some of the scales from his hands fell into the milk. My son drank freely of uncooked milk, the other inmates of the farm drinking home-brewed beer, and only taking milk in tea or coffee hot enough to destroy the vitality of fever germs. He alone suffered. This infection was the more remarkable, inasmuch as a few months previously he had been assisting a medical man in a crowded part of London where scarlet fever was prevalent, and had come into frequent contact with patients in different stages of the disease without suffering infection.

Had the milk from this farm been sent to London in the usual manner in cans, and the contents of these particular cans mixed with those of the rest received by the vendor, the whole of his stock might have been infected. As some thousands of farms contribute to the supplying of London with milk, the risk of such contact with infected hands occurring occasionally in one or another of them is very great, and fully justifies me in urgently recommending the manager of every household to strictly enforce the boiling of every drop of milk that enters the house. At the temperature of 212° the vitality of all dangerous germs is destroyed, and the boiling point of milk is a little above 212°. The temperature of tea or coffee, as ordinarily used, may do it, but is not to be relied upon. I need only refer generally to the cases of wholesale infection that have recently been traced to the milk of particular dairies, as the particulars are familiar to all who read the newspapers.

The necessity for boiling remains the same, whether we accept the germ theory or that of chemical poison, as such poison must be of organic origin, and, like other similar organic compounds, subject to dissociation or other alteration when heated to the boiling point of water.

It is an open question whether butter may or may not act as a dangerous carrier of such germs; whether they rise with the cream, survive the churning, and flourish among the fat. The subject is of vital importance, and yet, in spite of the research fund of the Royal Society, the British Association, &c., we have no data upon which to base even an approximately sound conclusion.

We may theorise, of course; we may suppose that the bacteria, bacilli, &c., which we see under the microscope to be continually wriggling about or driving along are doing so in order to obtain fresh food from the surrounding liquid, and therefore that if imprisoned in butter they would languish and die. We may point to the analogies of ferment germs which demand nitrogenous matter, and therefore suppose that the pestiferous wanderers cannot live upon a mere hydro-carbon like butter. On the other hand, we know that the germs of such things can remain dormant under conditions that are fatal to their parents, and develop forthwith when released and brought into new surroundings. These speculations are interesting enough, but in such a matter of life and death to ourselves and our children we require positive facts—direct microscopic or chemical evidence.

In the meantime the doubt is highly favourable to ‘bosch.’ To illustrate this, let us suppose the case of a cow grazing on a sewage-farm, manured from a district on which enteric fever has existed. The cow lies down, and its teats are soiled with liquid containing the chemical poison or the germs which are so fearfully malignant when taken internally. In the course of milking a thousandth part of a grain of the infected matter containing a few hundred germs enters the milk, and these germs increase and multiply. The cream that rises carries some of them with it, and they are thus in the butter, either dead or alive—we know not which, but have to accept the risk.

Now, take the case of ‘bosch.’ The cow is slaughtered. The waste fat—that before the days of palm oil and vaseline was sold for lubricating machinery—is skilfully prepared, made up into 2 lb. rolls, delicately wrapped in special muslin, or prettily moulded and fitted into ‘Normandy’ baskets. What is the risk in eating this?

None at all provided always the ‘bosch’ is not adulterated with cream-butter. The special disease germs do not survive the chemistry of digestion, do not pass through the glandular tissues of the follicles that secrete the living fat, and therefore, even though the cow should have fed on sewage grass, moistened with infected sewage water, its fat would not be poisoned.

What we require in connection with this is commercial honesty: that the thousands of tons of ‘bosch’ now annually made shall be sold as ‘bosch,’ or, if preferred, as ‘oleomargarine,’ or ‘butterine,’ or any other name that shall tell the truth. In order to render such commercial honesty possible to shopkeepers, more intelligence is demanded among their customers. A dealer, on whom I can rely, told me lately that if he offered the ‘bosch’ or ‘butterine’ to his other customers as he was then offering it to me, at 8½d. per lb. in 24-lb. box, or 9d. retail, he could not possibly sell it, and his reputation would be injured by admitting that he kept it; but that the same people who would be disgusted with it at 9d. will buy it freely at double the price as prime Devonshire fresh butter; and, he added, significantly, ‘I cannot afford to lose my business and be ruined because my customers are fools.’ To pastrycooks and others in business it is sold honestly enough for what it is, and used instead of butter.

In the ‘Journal of the Chemical Society’ for January 1844, page 92, is an account of experiments made by A. Mayer in order to determine the comparative nutritive value of ‘bosch’ and cream-butter. They were made on a man and a boy. The result was that on an average a little above 1½ per cent. less of the ‘bosch’ was absorbed into the system than of the cream-butter. This is a very trifling difference.

Before leaving the subject of animal food I may say a few words on the latest, and perhaps the greatest, triumph of science in reference to food supply—i.e. the successful solution of the great problem of preserving fresh meat for an almost indefinite length of time. It has long been known that meat which is frozen remains fresh. The Aberdeen whalers were in the habit of feasting their friends on returning home on joints that were taken out fresh from Aberdeen, and kept frozen during a long Arctic voyage. In Norway game is shot at the end of autumn, and kept in a frozen state for consumption during the whole winter and far into the spring.

The early attempts to apply the freezing process for the carriage of fresh meat from South America and Australia by using ice, or freezing mixtures of ice and salt, failed, but now all the difficulties are overcome by a simple application of the great principle of the conservation of energy, whereby the burning of coal may be made to produce a degree of cold proportionate to the amount of heat it gives out in burning.

Carcasses of sheep are thereby frozen to stony hardness immediately they are slaughtered in New Zealand and Australia, then packed in close refrigerated cars, carried to the ship, and there stowed in chambers refrigerated by the same means, and thus brought to England in the same state of stony hardness as that originally produced. I dined to-day on one of the legs of a sheep that I bought a week ago, and which was grazing at the Antipodes three months before. I prefer it to any English mutton ordinarily obtainable.

The grounds of this preference will be understood when I explain that English farmers, who manufacture mutton as a primary product, kill their sheep as soon as they are full grown, when a year old or less. They cannot afford to feed a sheep for two years longer merely to improve its flavour without adding to its weight. Country gentlemen, who do not care for expense, occasionally regale their friends on a haunch or saddle of three-year-old mutton, as a rare and costly luxury.

The Antipodean graziers are wool growers. Until lately mutton was merely used as manure, and even now it is but a secondary product. The wool crop improves year by year until the sheep is three or four years old; therefore it is not slaughtered until this age is attained; and thus the sheep sent to England are similar to those of the country squire, and such as the English farmer could not send to market under eighteenpence per pound.

There is, however, one drawback; but I have tested it thoroughly (having supplied my own table during the last six months with no other mutton than that from New Zealand), and find it so trifling as to be imperceptible unless critically looked for. It is simply that, in thawing, a small quantity of the juice of the meat oozes out. This is more than compensated by the superior richness and fulness of flavour of the meat itself, which is much darker in colour than young mutton. Legs of frozen mutton should be hung with the thick cut part upwards. With this precaution the loss of juice is but nominal. If the frozen sheep is not cut up until completely thawed and required for cooking there is no loss.

Another successful method of meat-preserving has been more lately introduced. It is based upon the remarkable antiseptic properties of boric acid (or boracic acid as it is sometimes named); this is the characteristic constituent of borax, and, like the fatty acids above described, has no sour flavour.

The speciality of this process, invented by Mr. Jones, a Gloucestershire surgeon, is the method by which a small quantity of the antiseptic is made to permeate the whole of the carcass.

The animal is rendered insensible, either by a stunning blow or by an anÆsthetic, with the heart still beating. A vein—usually the jugular—is opened, and a small quantity of blood let out. Then a corresponding quantity of a solution of boric acid, raised to blood heat, is made to flow into the vein from a vessel raised to a suitable height above it. The action of the heart carries this through all the capillary vessels into every part of the body of the animal. The completeness of this diffusion may be understood by reflecting on the fact that we cannot puncture any part of the body with the point of a needle without drawing blood from some of these vessels.

After the completion of this circulation the animal is bled to death in the usual manner. From three to four ounces of boric acid is sufficient for a sheep of average weight, and much of this comes away with the final bleeding. On April 2, 1884, I made a hearty meal on the roasted, boiled, and stewed flesh of a sheep that was killed on February 8, the carcass hanging in the meantime in the basement of the Society of Arts. It was perfectly fresh, and without any perceptible flavour of the boric acid: very tender, and full-flavoured as fresh meat. On July 19, 1884, I purchased a haunch of the prepared mutton, and hung it in an ill-constructed larder during the excessively hot weather that followed. On August 10, after twenty-two days of this severe ordeal, it was still in good condition. The 11th and 12th were two of the hottest days of the present century in England. On the 13th I examined the haunch very carefully, and detected symptoms of giving way. It had become softer, and was pervaded throughout with a slight malodour. On the 14th it became worse, and then I had it roasted. It was decidedly gamey; the fat, or rather the membranous junction between fat and lean, and the membranous sheaths of the muscles had succumbed, but the substance of the muscles, the firm lean parts of the meat, were quite eatable, and eaten by myself and other members of my family. There was no taste of boric acid, and the meat was unusually tender.

The curious element of this process is the very small quantity of the boric acid which does the work so effectually.

For some time past most of the milk that is supplied to London has been similarly treated by adding borax or a preparation chiefly composed of borax, and named ‘glacialine.’ This suppresses the incipient lactic fermentation, which, in the course of a few hours, otherwise produces the souring of milk, and thus prepared the milk remains for a long time unaltered.

The small quantity of borax that we thus imbibe with our tea, coffee, &c., is quite harmless. M. de Cyon, who has studied this subject experimentally, affirms that it is very beneficial.