After the apples have been pared, cored, and sliced, they are placed
in a tub of perfectly clean water, containing a small quantity of
salt, which prevents oxidation and discoloration. They are then cut
once vertically, and all bruises, specks, and parings trimmed away to
produce the well-known apple-rings of commerce. These are placed thinly
on one of the trays of the evaporator and entered at the lower end of
the upper flue. Sometimes a little sulphur may be sprinkled on the
furnace with great advantage for the purpose of bleaching the rings.
The first tray remains in the position just mentioned until the second
tray is ready to be placed under the first tray which will be in four
or five minutes; the third tray is then filled in the usual manner, and
placed under the second tray, and when the fourth tray is ready the
first three trays are pushed forward in the flue, and the fourth tray
takes the place of No. 1, and so on until the top flue is full. On the
arrival of the first tray at the upper end of the flue, the contents
are examined, and those that are sufficiently dried are removed, and
the remainder turned over and returned down the lower and cooler flue.
In many cases, one tray will hold the whole of the contents (which are
nearly dried) of two or three trays, the empty ones being taken away to
be again filled with fresh fruit. The degree of heat used for drying
apples is from 175° to 240° F.; and the time occupied varies from two
to four hours, according to the variety of the apple, but from two to
two and a half hours is the usual time. Whole apples require a much
longer time, eight to ten hours, according to size and variety.
Plums are dried in the same manner, except that they are placed in the
evaporator at once. They should be graded according to size, and be
uniformly ripe. During the process of evaporation plums ought to be
removed from the evaporator once or twice for the purpose of cooling
them and toughening the skin, and so prevent bursting, which they are
liable to do, because the skin does not allow the moisture in the fruit
to freely escape when first placed in the machine. As soon as the
plums commence to shrivel all danger of bursting is past, and they may
then remain in the evaporator until dry. The time required for plums
is from six to ten hours, and the temperature requisite 240° to 300°
F. Plums may be steamed for a few minutes and then split in half, thus
entirely dispensing with the cooling process, and considerably reducing
the length of time required in drying. 100 pounds of fresh plums will
give about 30 pounds of dried.
Apricots are simply cut in two, the stones being taken out, and the
fruit then dried just like apples, at from 240° to 250° F. They take
from two to three hours to dry. From 100 pounds of the fresh fruit, 10
to 12 pounds of dried will result.
Pears for drying purposes ought not to be quite ripe. They are peeled,
and either dried whole, or, more generally, are divided, and the
seed-vessels cut out, the stems being left on. They then require
steaming for eight or ten minutes, and are filled in from the bottom
upwards. The temperature used is 212° to 240° F., and the pears will
take five to seven hours to dry if divided, or seven to nine hours if
whole. From 100 pounds of fresh pears 12 to 16 pounds of dried ones
will be obtained. When preparing the pears before drying, the flavour
will be improved if a little sugar be added to the water in which
they are cooked, and to this may be put the juice of the removed
seed-vessels and peelings.
Vegetables require, in addition to the peeling, slicing, or cutting
up, to be steamed or cooked for five to seven minutes before they are
dried. This is necessary in order to keep their colour and to prevent
their becoming hard. When dried on a small scale the cooking in boiling
water is generally sufficient. Like apples, vegetables are always
filled in from below upwards.
French beans are cut into strips by a special machine, and cooked for
a few minutes. A little soda added to the water helps to preserve
their bright green colour. The time required for drying is from
three-quarters to one hour. Temperature 150° to 160° F. 100 pounds of
fresh beans giving 10 to 12 pounds of dry.
Peas require simply shelling and a few minutes’ cooking. They should
not be quite ripe, and are laid thinly on the trays. They take from one
to one and a half hours to dry. Temperature 212° to 220° F. 100 pounds
of green pods will yield about 10 to 12 pounds of dried peas.