Artificial evapora tion.
In the process of evaporating, two dis tinct methods are followed : one, by means of air heated by stoves or fur naces and then made to circulate through the drying fruit; the other, an indirect system, by means of steam-pipes that pass through the evaporator. The latter system has not yet been generally employed, but it has many points in its favor and seems likely to replace the direct-heating system in large evaporators.
There are three general types of construction of the direct-heating system : the cabinet, the kiln, and the tower or fine.
Cabinet evaporators.— The cabinet evaporators usually consist of a series of drawers with screen bottoms, placed above a furnace or stove so that the hot air passes up through the fruit. Sometimes the floor under the lower screen is solid, with open ings at the sides. The hot air strikes this floor, is divided into two currents that pass up on the sides, then over the fruit to the center of the evaporator and out at the top. Fig. 255 shows an evaporator of this type. In these evaporators, the fresh fruit is usually placed in the upper drawer. When that on the lower screen is sufficiently dried, it is removed and each screen is lowered one space, making room for a new screen in the top space. Usually there are two series of drawers carrying twenty to twenty-five screens, which are one to four feet square, according to the size of the evaporator.
There are many sizes and styles of these cabinet evaporators. Some are small enough to stand on the kitchen stove (Figs. 256, 257), cost three to five dollars, and have a capacity of one to four pecks per day. Fig. 258 shows one of a larger size, made of galvanized iron and provided with its own fur nace. This has twenty 12 x 24-inch screens, and has a capacity of four to five bushels per day.
Larger evaporators constructed by farmers usually consist of a wooden building on a brick basement, in which the furnace or stove is placed. The stove pipe is carried around the basement so as to get the full benefit of the heat. These usually have two
compartments, each of which has room for ten to twelve screens that are about four feet square.
Another form of cabinet evaporator sometimes used is made with doors at the front and at the back, and is much larger, so that there is room for six to ten screens on one plane. Each newly filled screen is put in at the highest level, and as it goes in it pushes the preceding one toward the back. When the first one reaches the back, it is put in the next lower level and started toward the front again. The screens are thus run back and forth till they come out at the lowest level when the fruit is sufficiently dried.
Because of their cheapness and simplicity, the cabinet evaporators are very popular with begin ners and with small growers. The smaller ones are well adapted to evaporating for home use.
Kiln evaporators.—The kiln evaporator is simply a room with a slatted floor, underneath which air pipes or smoke-pipes from a stove or furnace are conducted. The buildings are usually constructed with double walls or with some other device for retaining the heat. The drying floor is placed about nine to twelve feet above the floor of the furnace room. It is made of slats of hard wood that are about one inch wide on top and one-half inch wide at the bottom, so that they have cracks one-eighth to one-fourth inch wide. The cracks are larger on the lower side, so as to prevent clog ging. On such a floor, hops, apples, pears, rasp herries,and the like are evapo rated. Fig.260 shows such a kiln filled with apples. This kiln is the com mon size in New York, 20 x 20 feet, and will evaporate hundred bushels of ap ples per day, or more if run all night. In this evaporator, two men had charge of the furnace and of six kilns that were evaporating 400 bushels per day. Fig. 261 gives the outside view of a five-kiln evaporator of this type. It shows the ventilator at the ridge, where the hot air escapes after passing over the fruit.