Hot-air process.—Great quantities of vegetables continue to be prepared by this process, which has been in use for some time by Whitehead, and other well-known firms. A common method of conducting the operation is as follows :—The fruit or vegetable is pared and cored, if necessary, and then finely shredded. The shreds are spread on galvanized-iron wire screens in the evaporator, a 3-storeyed chamber, through which passes a current of air heated to 116°(240° F.). The screens rest on endless chains, that move upwards at intervals of 3-5 minutes, when a fresh screen is put on below, and a finished one is taken off at the top. The evaporation is very rapid. The cores and peelings of apples, &c., are made into vinegar.
Another plan is by means of a vacuum-pan, heated to 49°-77° (120°-170° F.). The air is dried by passage over chloride of calcium. The operation occupies 20 minutes.
Masson and Gannal's process.—Vegetables are submitted for a few minutes to steam at 70 lb. a sq. in., then dried by air at 100° (212° F.), subjected to hydraulic pressure so as to form tablets, and, when required for use, are soaked in cold water for 5 hours.
Carsten's process fur Potatoes.—The potatoes are peeled and cut into discs, and are scalded by immersion in nearly boiling water. They are then dried hard in an oven. To preserve the white colour, they are treated with water, acidulated with 1 per cent. of sulphuric) acid. They are then washed in cold water, and dried.
Quick-lime for Potatoes.—Fo• preserving potatoes in store, the floor is sprinkled with fine quicklime; this is covered with a layer (4-5 in. thick) of potatoes; this by a sprinkling of quiok lime again, and so on, using the lime in the proportion of about 1 measure to 40 measures of potatoes. This method checks disease when it is present, and improves the potatoes if they are watery or waxy. Layers of straw and powdered plaster of Paris may be substituted for the lime.
Sacc's process.—Sacc's process for preserving vegetables is as follows :—The vegetables are warmed to destroy their rigidity, and are then packed in barrels, and surrounded with + their weight of acetate of soda in powder, by which their moisture is absorbed. In summer, the action is immediate ; but in winter, it may be necessary to put the barrels into a room heated to 20° (68°F.). After 24 hours, the vegetables are removed, and kept in tf. dry atmosphere. For use, they are soaked in cold water for 12 hours.
Cooxarci.—The preservation of vegetables by cooking them in sealed cases is dependent upon
the destruction of all organic germs by the heat of the boiling, and the perfect exclusion of air. An example of the simplest form is the Canning of Tomatoes.—The fruits are scalded to loosen the skin, and then dipped in sieves into water, heated by injection of steam, for 2 minute. They are then skinned, and picked over, and passed into the steamer. Thence they fall into the hopper, and are fed by the " stuffer," a cylinder worked by a treadle, into the cans. The filling of these is adjusted by boys, and they are sealed up. The cans are then boiled for 2 hours, then partially cooled, the air is let out by a pin-hole, and they are immediately soldered up, and the cooling is completed.
Many other vegetables are canned in a similar manner. Those which have a green colour lose it during the operation, by the destruction of the chlorophyl. The same remark applies to those dried by heat. The green colour may be replaced by adding a solution of chlorophyl, exhausted from other plants ; or the natural colour may be retained by treatment with alkaline earths, according to Possoz, Biardot, and Lecuyer.
PicituNe.—In pickling vegetable substances, advantage is taken of the curative properties of acids, alcohol, sugar, saltpetre, salt, &c.
By Adds.—Curing by means of acids, as acetic acid, vinegar, &c., is the process commonly known as "pickling." In the ordinary way, the vegetables are kept soaking for a long time in brine, and are then pickled by acetic acid. An improved method, by which months of time are saved, is to exhaust them under an air-pump, and then to force in spiced vinegar under a pressure of 45 lb. a sq. in.
By Alcohol.—This is too expensive for commercial purposes. An example is the preservation of cherries in brandy.
By Sugar.—Sugar is very largely used for preserving fruit in an edible condition, either in bulk, or in separate pieces.
Marmalade.—The manufacture of marmalade is a type of the process carried on in bulk. The peel is removed from the oranges, and their pulp is squeezed, to liberate the juice. The peel is softened by steaming, and is then sliced by revolving knives. The pulp is boiled, and then passed through a " searcher," to remove the tough skin and pips. The juice and sliced peel are then mixed and boiled with lump sugar in steam-jacketed copper pans. Wherever possible, the appliances used are of oak.