3. Various kinds of salt are used in the preservation of food. Saltpetre and sal prunella (which is saltpetre deprived of its water of crystallization by heat) are also used for the purpose. The action of these alkaline salts upon animal substances is, as already noticed, to abstract the water in the juices of the meat, and, being dissolved therein, the salts enter the pores of the animal substance; the albumen of the meat, which is more liable to putrefaction than the gelatine and fibrine, is thus rendered less so. There are two methods of salting, dry salting and pickling. In dry salting, the meat is packed in dry salt, or in some cases the surface is rubbed all over with salt. In pickling, the meat is kept immersed in a solution (sometimes saturated) of common salt dissolved in water. This method does not render the meat so salt as dry rubbing, and is probably less injurious to its nutritious qualities, but it will not keep the meat so well. Bacon is cured by salting and drying, for which latter purpose it is often hung up in the wide chimneys of farm-house kitchens; cod is also salted and dried for the large demand of the Peninsula; in England, it is used in a green state; that is, instead of being split quite open, it is only opened down to the navel, then salted, and laid in brine or strong pickle, and put into casks without drying. Haddock, cod, or ling, are cured by splitting the fish and removing the backbone; they are then salted for two or three days, with equal parts of salt and sugar, or with salt alone; they are next stretched on sticks, and laid on the beach to dry in the sun, or they are arranged on stages, or hung up in an inclosed space warmed by a stove. Herrings are salted, or pickled, and smoked.
Sugar, like salt, takes away the water from animal substances, and thus prevents putrefaction. By immersing meat in molasses, it has been preserved fresh for months. Fish is sometimes preserved by cutting it open, rubbing in sugar, and leaving it for a few days; it is then dried in the air, taking care to turn it frequently. For a salmon of six pounds weight, a table-spoonful of brown sugar is sufficient; but, if hardness be required, a teaspoonful of saltpetre is to be added.
4. The efficacy of smoking, or smoke-drying, arises not only from the heat of the smoke, but from certain chemical products disengaged during the combustion of the wood fuel used for the purpose. Pyroligneous acid vapor and creasote are both produced, and the latter substance possesses the remarkable property of coagulating albumen. Hence, those chimneys only are fit for the purpose where the fire below is wood or peat, not coal. The kind of wood burnt is also of importance, the smoke from beech and oak being preferable to that from fir or larch. Smoke from the twigs of juniper, rosemary, peppermint, &c., impart to the meat a portion of their aromatic flavor. Westphalia hams owe some of their excellence to being smoked by juniper. Slow smoking is preferable to rapid, as it penetrates completely into the interior of the meat. In some parts of the country, the drying and smoking of hams are a separate trade. In such cases, a smoking-house or hut is erected, about twelve feet square, and the walls seven feet high, with a hole in the roof; joists are laid across inside, to hang the flitches on, and the floor is covered five or six inches deep with sawdust, which, being kindled, produces much smoke and little flame.
5. Vinegar and some other acids preserve both animal and vegetable substances by coagulating their albumen, which, as already stated, is peculiarly liable to putrefactive fermentation.
6. In the year 1810, M. Appert received a reward of 12,000 francs from the French Government for his method of parboiling provisions, and inclosing them in earthenware vessels in such a manner as to exclude the air. Many vegetables, fruits, &c., can be kept fresh for a great length of time, by shutting them up closely in a vessel, having previously filled up the interstices with sand or other loose substance that will exclude nearly all the air. Fresh walnuts may be preserved in this way in a jar, packed with sand and closely covered over; grapes packed in sawdust are imported into this country. Meat cannot be preserved in this way, but by exposing it to the heat of boiling water, the albumen, in which putrefaction first commences, coagulates; and as coagulated albumen is somewhat slow in decomposing, we thus have a reason for the common observation that cooked meat will keep longer than raw. It will not, however, keep many days, unless the air be perfectly excluded, not only from the external, but from the internal parts. The air in the interior may be expelled by boiling, and the exterior air may be kept away by inclosing the substance in an air-tight vessel. If these conditions be carefully observed, food may be preserved for any length of time. Appert's method consists in applying heat to the substances to be preserved, so as to coagulate their fermentable juices, and then to place them in such a situation as to deprive them of contact with air. The vessel in which the meat is prepared is plunged for some time into boiling water before it is finally sealed, in order to drive out the last portions of the air; for, if a small portion of oxygen gas were present, this would be sufficient to commence the process of fermentation, and when once begun it would be continued.
M. Appert's process may be described as follows:—
The meat to be preserved is first parboiled, or somewhat more, and freed from the bones. It is then put, together with vegetables, if required, into tin cases or canisters, which are filled quite up with a rich gravy; a tin cover, with a small aperture in it, is then carefully fixed on to each canister by solder, and while the vessel is perfectly full, it is placed in boiling water, or in a saline bath, heated above the boiling point of water, and kept therein until the air has been expelled as completely as possible by the steam generated within the canister. The small hole in the cover is completely closed up with a little solder while the contents are yet hot, the issue of the steam being stopped for a moment by means of a damp sponge. The canister, with its ingredients, is now allowed to cool, in consequence of which these contract, and the sides of the vessel are forced slightly inwards by the pressure of the atmosphere, and become a little concave. As a precautionary measure, however, the tins are placed in the testing-room, which is heated to above 100° Fahr. Should putrefaction take place in consequence of a minute portion of oxygen left in the case, and not combined with the animal or vegetable matter, the generated gases will burst the canisters; those, however, which withstand this test will preserve the provisions for many years; for as each vessel is hermetically sealed, and all access of air prevented, it may be sent into any climate without fear of putrefaction, and the most delicate food of one country be thus eaten in its original perfection in a distant region, many months, or even years after its preparation. In this manner may all kinds of alimentary substances be preserved; beef, mutton, veal, and poultry; fish and game; soups, broths, and vegetables; creams and custards. Of a quantity taken by Captain Nash to India, not one canister was spoiled; and one which he brought back contained, after two years, beef in the highest state of perfection and preservation, and after having been carried upwards of 35,000 miles, in the warmest climates. This method has been adopted by the commissioners for victualling the English Navy, who, having examined some meat so preserved for four years, during voyages in the Mediterranean, found it as sound, sweet, and fresh, as if it had been boiled only the day before. Captain Basil Hall bears similar testimony. It was stated, however, by the officers in the Antarctic voyage, that they gradually got very tired of preserved meats, but not of preserved vegetables, and that there was an insipidity in them which they did not find in fresh food. There is, however, no doubt that, if the articles be selected with care, and the process be properly conducted, M. Appert's method of preserving food is a valuable invention. If the contractor be careless or dishonest, the most fearful consequences might ensue to the crews of ships victualled with preserved meats. It appears, from a recent examination of several thousand canisters of the preserved meat of the Navy at Portsmouth, England, that their contents were masses of putrefaction, consisting of meat, &c., which, even in a fresh state, ought never to be used as food. It is stated that this preserved meat was supplied from Galatz, in Moldavia.
In 1842, M. Appert's method was made the subject of a further patent, granted to Mr. Bevan, whose process consisted in expelling air from the cases containing the food, by placing such cases in connection with a vacuum chamber, or other exhausting apparatus, and also with a vessel containing gelatine or other suitable fluid material, in such a manner that, by opening the communications, the air escapes into the exhausting apparatus and the gelatine takes its place. By this method the high temperature previously used in preserving food was not required; it could, on the contrary, be cooked at very low temperatures, and in a space almost void of air. The apparatus used is shown in section, in the following figure: A is a vessel open at the top, and filled to the line i with fluid gelatine, having a pipe j, and a stopcock e firmly attached to it. B is a sphere of metal in which a vacuum is produced by blowing steam through it by the pipe l out through k; l and k are then closed, and a jet of water at m, applied to the outside of the sphere, condenses the steam and leaves a vacuum within it. The substance to be preserved is inclosed within a cylindrical tin vessel C, the top of which is then soldered on, and two small metal pipes d and c passed into it air-tight, as far as a b; the other ends being secure to the pipes j j at h h. The case is next immersed in a water-bath N, at a temperature of about 120°, and by turning the cock f, the greater portion of the air in the case C rushes into B; the article of food, animal or vegetable, in the case, being thus relieved of atmospheric pressure, the heat of 120° is sufficient to cook it, and to expel the air from it. A fowl is cooked in this way in about fifteen minutes. The cock e is then opened, and the gelatine, kept fluid by the warm bath P, enters by the pipes j and c, into the case C, and drives the small portion of air left therein into the vacuum chamber B. The case C is then hermetically sealed by nipping the tubes d and c at the points g g. The case is then submitted for a few minutes to the action of boiling water (thirty minutes for a fowl), and when cool, the process is complete.
A concentrated form of food, called meat biscuit, excited a considerable degree of attention in the Great Exhibition. It is formed by boiling down the fresh beef of Texas, and mixing into the strong beef-tea thus formed a certain proportion of the finest flour. The biscuit formed from these materials is so nutritive, that less than four ounces a day (mixed with warm water or not, according to circumstances) is sufficient food for a man in active service. It is very light and portable, and keeps perfectly well without change; hence it is admirably adapted to the provisioning of troops, ships, and overland expeditions. The manufacture is also of great importance to those countries in which cattle are superabundant, and are killed merely for the sake of their skins for the tanner, or their bones for the farmer, the flesh being actually thrown away. In some places, animals which we are accustomed to regard as valuable are so numerous that they are drowned by hundreds, merely to get rid of them, neither their skin, bones, nor flesh serving as a pretext for the wholesale slaughter.