45. Although, as has just been pointed out, moisture is required for the
growth of some micro-organisms, both moisture and warmth are necessary
for the growth of most of the organisms that cause molding,
putrefaction, and fermentation. It is definitely known, also, that in
winter or in cold climates food can be kept for long periods of time
without any apparent change; in fact, the lower the temperature the less
likely are foods to spoil, although freezing renders many of them unfit
for use. These facts are what led up to the scientific truth that
keeping foods dry and at a low temperature is an effective and
convenient method of preventing them from spoiling and to the invention
of the refrigerator and other devices and methods for the cold
storage of foods.
46. THE REFRIGERATOR.--For home use, the refrigerator offers the most
convenient means of keeping foods in good condition. As is well known,
it is a device that, by means of air cooled by the melting of ice or in
some other manner, keeps food at a temperature near the freezing point.
All refrigerators are constructed in a similar manner, having two or
more layers of wood between which is placed an insulating material, such
as cork, asbestos, or mineral wool. The food compartments are lined with
tile, zinc, or other rust-proof material, and the ice compartment is
usually lined with rust-proof metal, so as to be water-tight and
unbreakable. Any refrigerator may be made to serve the purpose of
preserving food effectively if it is well constructed, the ice chamber
kept as full of ice as possible, and the housewife knows how to arrange
the foods in the food chambers to the best advantage.
The construction and use of refrigerators are based on the well-known
scientific fact that air expands and rises when it becomes warm. This
can be proved by testing the air near the ceiling of a room, for no
matter how warm it is near the floor it will always be warmer above. The
same thing occurs in a refrigerator. As air comes in contact with the
ice, it is cooled and falls, and the warm air is forced up. Thus the air
is kept in constant motion, or circulation.
[Illustration: Fig 12.]
47. Many refrigerators are built with the ice compartment on one side,
as in the refrigerator illustrated in Fig. 12. In such refrigerators,
there is usually a small food compartment directly under the ice
chamber, and this is the coldest place in the refrigerator. Here should
be stored the foods that need special care or that absorb odors and
flavors readily, such as milk, butter, cream, meat, etc., because at
this place the air, which circulates in the manner indicated by the
arrow, is the purest. The foods that give off odors strong enough to
taint others should be kept on the upper shelves of the refrigerator,
through which the current of air passes last before being freed from
odors by passing over the ice.
48. In Fig. 13 is shown a type of refrigerator in which the ice chamber,
or compartment, extends across the entire top. This type is so built as
to produce on each side a current of air that passes down from the ice
at the center and back up to the ice near the outside walls, as shown by
the arrows. A different arrangement is required for the food in this
kind of refrigerator, those which give off odors and flavors being
placed in the bottom compartment, or farthest from the ice, and those
which take up odors and flavors, on the top shelf, or nearest the ice. A
careful study of both Figs. 12 and 13 is advised, for they show the best
arrangement of food in each type of refrigerator.
[Illustration: Fig. 13]
49. CARE OF FOOD IN REFRIGERATOR.--The proper placing of foods in a
refrigerator is extremely important, but certain precautions should be
taken with regard to the food itself. Cooked foods should never be
placed in the refrigerator without first allowing them to cool, for the
steam given off when a dish of hot food comes in contact with the cold
air makes the refrigerator damp and causes an undue waste of ice by
warming the air. All dishes containing food should be wiped dry and
carefully covered before they are placed in the refrigerator, so as to
keep unnecessary moisture out of it. As butter and milk are likely to
become contaminated with odors given off by other foods, they should be
properly protected if there is not a separate compartment in which to
keep them. The milk bottles should always be closed and the butter
carefully wrapped or put in a covered receptacle. Onions, cabbage, and
other foods with strong odors, when placed in the refrigerator, should
be kept in tightly closed jars or dishes, so that the odors will not
escape. Before fresh fruits and perishable vegetables--that is,
vegetables that decay easily--are put into the refrigerator, they should
be carefully looked over and all decayed portions removed from them. No
food should be placed in the ice chamber, because this will cause the
ice to melt unnecessarily.
50. CARE OF THE REFRIGERATOR.--It is essential that all parts of the
refrigerator be kept scrupulously clean and as dry as possible. To
accomplish this, nothing should be allowed to spoil in it, and anything
spilled in the refrigerator should be cleaned out immediately. The foods
that are left over should be carefully inspected every day, and anything
not likely to be used within a day or so should be disposed of. At least
once a week the food should be removed from all compartments, the racks
taken out, the drain pipe disconnected, and each part thoroughly washed,
rinsed with boiling water, and dried. The inside of the refrigerator
should likewise be washed, rinsed, and wiped dry, after which the drain
pipe should be connected, the shelves put back in place, and the
food replaced.
The ice chamber of the refrigerator should also be cleaned frequently,
the best time to do this being when the ice has melted enough to be
lifted out conveniently. To prevent the ice from melting rapidly when it
is out of the refrigerator, it may be wrapped in paper or a piece of old
blanket, but this covering must be removed when the ice is replaced in
the chamber, in order to allow the ice to melt in the refrigerator.
Otherwise, it would be impossible to chill the refrigerator properly,
the temperature remaining the same as that outside, for it is as the ice
gradually melts that the air in the refrigerator becomes cool. Of
course, every effort should be made to keep the ice from wasting.
Therefore, while the refrigerator should be kept in a convenient place,
it should not be exposed to too great heat; also, the doors should be
kept tightly closed, and, as has already been explained, hot foods
should not be put in until they are sufficiently cooled. Attention must
be given to the care of the refrigerator, for only when it is clean and
dry can the growth of bacteria that attack foods be prevented.