Eggs, after being laid, lose daily, by transpiration, a portion of the
matter which they contain, notwithstanding the compact texture of their
shell, and of the close tissue of the flexible membranes lining the
shell, and enveloping the white. When an egg is fresh, it is full,
without any vacancy; and this is a matter of common observation, whether
it be broken raw, or when it is either soft or hard-boiled. In all stale
eggs, on the contrary, there is uniformly more or less vacancy,
proportioned to the loss they have sustained by transpiration; hence,
in order to judge of the freshness of an egg, it is usual to hold it up
to the light, when the transparency of the shell makes it appear whether
or not there is any vacancy in the upper portion, as well as whether the
yolk and white are mingled and muddy, by the rotting and bursting of
their enveloping membranes.
The transpiration of eggs, besides, is proportional to the temperature
in which they are placed, cold retarding and heat promoting the process;
hence, by keeping fresh-lain eggs in a cool cellar, or, better still, in
an ice-house, they will transpire less, and be preserved for a longer
period sound, than if they are kept in a warm place, or exposed to the
sun's light, which has also a good effect in promoting the exhalation of
moisture. As, therefore, fermentation and putridity can only take place
by communication with the air at a moderate temperature, such connection
must be excluded by closing the pores of the shell.
It is an indispensable condition of the material used for this purpose,
that it shall be incapable of being dissolved by the moisture transpired
from the interior. Spirits of wine varnish, made with lac, answers the
requirement; this is not very expensive, but is rather an uncommon
article in country places, where eggs are most abundantly produced.
A better material is a mixture of mutton and beef suet, which should be
melted together over a slow fire, and strained through a linen cloth
into an earthen pan. The chief advantage in the use of this is, that the
eggs rubbed over with it will boil as quickly as if nothing had been
done to them, the fat melting off as soon as they touch the water. The
transpiration is as effectually stopped by the thinnest layer of fat as
by a thick coating, provided that no sensible vestige be left on the
surface of the shell. All sorts of fat, grease, or oil are well adapted
to this purpose; by means of butter, hog's lard, olive oil, and similar
substances, eggs maybe preserved for nine months as fresh as the day
upon which they were laid.
Another method is, to dip each egg into melted pork-lard, rubbing it
into the shell with the finger, and pack them in old fig-drums, or
butter firkins, setting every egg upright, with the small end downward.
Or, the eggs may be packed in the same way in an upright earthen pan;
then cut some rough sheep's tallow, procured the same day that the
animal is killed, into small pieces, and melt it down; strain it from
the scraps, and pour it while warm, not hot, over the eggs in the jar
till they are completely covered. When all is cold and firm, set the
vessel in a cool, dry place till the contents are wanted.
Eggs will also keep well when preserved in salt, by arranging them in a
barrel, first a layer of salt, then a layer of eggs, alternately. This
can, however, also act mechanically, like bran or saw-dust, so long as
the salt continues dry; for, in that case, the chlorine, which is the
antiseptic principle of the salt, is not evolved. When the salt,
however, becomes damp, its preservative principle will be brought into
action, and may penetrate through the pores of the shell.
Immersing eggs in vitriol, or sulphuric acid, is likewise a very
effectual means of preserving them; the sulphuric acid acts chemically
upon the carbonate of lime in the shell, by setting free the carbonic
acid gas, while it unites with the lime, and forms sulphate of lime, or
plaster of Paris. Another method is, to mix together a bushel of
quick-lime, two pounds of salt, and eight ounces of cream of tartar,
adding a sufficient quantity of water, so that eggs may be plunged into
the paint. When a paste is made of this consistence, the eggs are put
into it, and may be kept fresh, it is said, for two years.
Another method of preserving eggs a long while fresh, depends upon a
very different principle. Eggs that have not been rendered reproductive
by the cock have been found to continue very uncorrupted. In order,
therefore, to have eggs keep fresh from spring to the middle or even to
the end of Winter, it is only necessary to deprive the hens of all
communication with the cocks, for at least a month before the eggs are
put away.
It ought not to be overlooked, in this connection, that eggs not only
spoil by the transpiration of their moisture and the putrid fermentation
of their contents, in consequence of air penetrating through the pores
of the shell, but also by being moved about and jostled, when carried to
a distance by sea or land. Any kind of rough motion, indeed, ruptures
the membranes which keep the white, the yolk, and the germ of the
chicken in their appropriate places; and, upon these being mixed,
putrefaction is promoted.