Preserved Provisions. Under the term preserves is usually included fruit, eaten whole or broken, or the juice of fruit, preserved by boiling with sugar. Whole fruit is boiled in clear syrup in such a manner that the sugar penetrates the fruit completely. It is then drained and dried at a gentle heat, so that the absorbed sugar crystallises in the substance and on the surface of the fruit, which is then known as candied. Jam consists of fruit boiled with an equal weight of sugar, which latter dissolves in the fruit juice set free as the fruit breaks down. If well made they can be preserved in this manner for years, but the quality deteriorates after twelve or eighteen months, owing to crystallisation and other changes taking place in the sugar. Fruit jellies consist of the juice of the fruit only, boiled with sugar, this vegetable jelly consisting principally of a substance known to chemists under the name of pectin. Fruits are also preserved by covering with water in suitable vessels, heating to a high temperature, and closing the vessel whilst hot.
Meat, vegetables, and other provisions may be preserved with more or less success in a number of ways, which may be classed roughly under four headings: (1) desiccation; (2) use of cold; (3) by chemical compounds (antiseptics); (4) by exclusion of air. The simple process of drying is effective both with meat and vegetables, and if completely carried out prevents the ordinary putrefactive changes from taking place. Dried vegetables are prepared largely for use on board ship, and the soup tablets so extensively used nowadays consist of meat and vegetables dried and pressed together. Jerked Beef (q.v.) and Pemmican (q.v.) are prepared chiefly by drying in the sun. The use of cold is mainly a temporary expedient employed for the carriage of meat from one country to another. This industry is carried on extensively in America, Australia, and New Zealand. The carcass is frozen hard by a refrigerating machine, and packed on board ship in a chamber cooled by a similar apparatus. Meat so preserved arrives in Europe in good condition, and if properly thawed is superior to all but the best home-grown beef and mutton (see REFRIGERATION). For condensed milk, see MILK.
Certain chemical substances have the power to prevent decay or arrest putrefactive changes, by destroying the activity of the germs or ferments which act as the exciting cause. Common salt is variously applied for the purpose of preserving meat (the food-value being thereby somewhat decreased); the meat may be immersed in brine, packed in salt, ribbed with salt and dried, or salted and smoked. The method of salting and smoking ham is described at HAM; the chief preservative element in the wood-smoke is creasote. Creasote, boric acid, salicylic acid, and sulphur compounds are all substances that can be used as food preservatives, but the objection to the use of chemical agents is that they either have a distinct taste themselves or have a toxic influence on the human body. Salicylic acid has been used in large quantities for preserving milk and other foods, but, when taken even in small doses for a lengthened period, it disturbs the animal economy; and in France any food preserved by its means is now condemned as unfit for human consumption. The use of creasote is confined to meats which are usually smoked. Boric acid has no taste, and in all probability is harmless when taken in the small quantities present in food preserved by its means. Milk, fish, poultry, and meat of all kinds may be preserved for months by its use. A very ingenious method of using this preservative has been tried with success. The boric acid is injected into the large vein of an insensible but living animal, so that it is carried in the ordinary circulation to all parts of the body, and the animal is then killed; meat so prepared has been kept fresh and palatable for about three months. Some sulphur compounds, notably the bisulphite of lime and sulphurous acid, are good preservatives, but they have an objectionable taste. The former is used by butchers as a preserver of meat in hot weather.
Exclusion of air is a method of preserving which is used almost exclusively for cooked foods. Various plans of coating meat with air-tight coating have been tried, but they have been carried little further than the experimental stage. Meat has been dipped in molten paraffin-wax, gelatine, gutta-percha, &c.—all of which exclude air; but the air, or, more correctly, the germs present in the air, are imprisoned in the tissues of the meat, and these speedily set up putrefactive changes. The only process which has successfully accomplished the desired end is by the use of high temperature to expel the air and destroy the germs, and then sealing to prevent ingress of more air. Many have claimed the credit of this invention, but in all probability it was first proposed by a M. Appert of Paris in 1810. The process as now carried on, however, is the outcome of many minds, Appert's original method simply supplying the groundwork. The various tinned meats, soups, &c. now in the market are examples of this method of preserving food. The meat, &c. is placed in tins, which are immersed in a solution of calcium chloride heated up to a temperature of 270° F., which destroys both germs and spores. The tins are previously closed, except a small pin-hole for the escape of steam. They are heated thus for about three hours, when the pin-holes are closed by solder, and the tins are allowed to cool. This process is thoroughly successful as far as mere preservation goes. Tins of meat thus treated have been opened after twenty years, and no sign of putrefaction has been noted; occasionally through some carelessness the air may not have been thoroughly removed and putrefaction ensues; such exceptions, however, are rarely met with in tins sent out by good firms. A bad tin can be detected before opening by the bulged-out appearance of the tin, the gases of decomposition pressing out the sides or ends. The objection to the process lies in the over-cooking to which the meat must be subjected. This impairs both the appearance and flavour, and no doubt removes some of the nutritive value of the meat, although this latter point is denied by some. Other plans, varying somewhat in detail but similar in principle, have been patented, and are in use in some of the food-preserving factories. Aberdeen and London are centres for this industry, the former having five factories, whilst in America and New Zealand (q.v.) a large amount of capital is invested in the trade. See SALMON.
The various extracts of meat are in a way preserved foods. They consist of the juice and extractive matter of the meat evaporated down to a thick consistence, and frequently preserved by a large addition of salt. The majority of these extracts are stimulants rather than foods, some of them being practically useless. Vegetables are frequently preserved by the process of pickling. The vegetables are boiled with vinegar and spices. The latter two substances, being antiseptic in their nature, prevent putrefaction and decay. For the preservation of wood, see DRY ROT.