United States. Bureau of Animal Industry.

Circular (United States. Bureau of Animal Industry). no. 138-150a, 1909-11 online

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Online LibraryUnited States. Bureau of Animal IndustryCircular (United States. Bureau of Animal Industry). no. 138-150a, 1909-11 → online text (page 5 of 21)
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shock during a warm July rain would probably be swarming with
bacteria and be absolutely unfit for food, while another egg stored
eight months in a first-class cold-storage room would be of much
better quality.


Eggs are among the most difficult of food products to grade. This
is because each egg must be considered separately, and because the
actual substance of the egg can not be examined without destroying
the egg.

From external appearance eggs can be selected for size, color, clean-
liness of shell, and freedom from cracks. This is the common method
of grading in early spring, when the eggs are uniformly of good
quality. Later in the season the egg candle is used. In the technical
sense any kind of a light may be used for an egg candle. A 16-candle-
power electric lamp is the most desirable. The light is inclosed in a
box or a tin cylinder, in which are made openings about the size of a
half dollar. The room being darkened, the candler holds the egg to
the light, large end upward, and gives it a quick turn in order to
view all sides and to cause the contents to whirl within the shell.

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(See fig. 1.) To the expert this process reveals the actual condition
of the egg to an extent that the novice can hardly realize. The art
of egg candling can not be readily taught by worded description.
One who wishes to learn it had best go to an adept, or he may begin
unaided and by breaking many eggs learn the essential points.

Fig. 1. — Candling and sorting eggs. (The No. 2 quality eggs are placed in a box to the left
of the candler, which is hidden from view in the picture. This picture was taken by
flash light, as candling must be done in a dark place.)


Eggs when laid differ considerably in size, but otherwise are a
very uniform product. The purpose of the egg in nature requires
that this be the case, because the contents of the egg must be so pro-

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portioned as to form the chick without surplus or waste, and this
requires a chemical composition that varies but slightly.

For food purposes all fresh eggs are practically equal. The tint
of the yolk varies somewhat, being more yellow when green feed has
been supplied the hens. Occasionally when hens eat unusual quan-
tities of green feed the yolks show a greenish-brown tint and appear
dark to the candle. Such eggs are called " grass eggs." They are
perfectly wholesome.

An opinion exists among egg men that the white of the spring egg
is of finer quality and will " stand up " better than that of summer
eggs. This is true enough of commercial eggs, but the difference is
chiefly, if not entirely, due to external factors that act upon the egg
after it is laid.

The flavor or odor of an egg may be noticeably influenced by the
feed of the hen. This has been demonstrated by feeding hens heavily
on onion tops or garlic. So far as is known to the writer, no practi-
cal application has been made of this principle.

There are some other peculiarities that may exist in eggs at the
time of laying, such as blood clots inclosed within the egg, a broken
yolk, or perhaps bacterial contamination. The so-called "tape-
worms" of eggs are detached portions of the lining membrane.
" Liver spots " or " meat spots " are detached folds from the walls
of the oviduct. All such abnormalities are rare, difficult to detect or
prevent, and are so inconsequential when compared with the eggs
which are spoiled after laying that further consideration will not be
given to them.


The shells of eggs vary in shape, color, and firmness. These varia-
tions are more a matter of breed and the individuality of the hen
than of care or feed. The strength of eggshells is important, be-
cause breakage is a source of considerable loss to the trade. How-
ever, the difficulty of weak-shelled eggs is not one which can be easily
remedied. Nothing more can be advised than to feed a ration con-
taining plenty of mineral matter and to discard hens that lay notice-
ably weak-shelled or irregularly shaped eggs.

The color of eggshells is a matter in regard to which more has per-
haps been said in poultry papers than the trade facts warrant. It is
commonly stated that Boston and surrounding towns want brown
eggs, while New York and San Francisco demand white eggs. These
trade fancies probably result from the fact that there are large hen-
neries in the respective localities producing eggs of the favored color.
If the eggs from such farms are the best in the market and are uni-

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formly of a particular shade, that mark of distinction, like the trade
name on a popular article, would naturally become a selling point.
Only the select trade, even in the cities mentioned, considers the color
in buying. Uniformity of appearance in color as well as in other
points pleases the eye, and for that reason and no other should dis-
tinction be made. Eggs of all Mediterranean breeds are white, those
of Asiatics are brown, and those of American breeds are usually
brown, but not of so uniform a tint.


The size of eggs is chiefly controlled by the breed or by selection of
layers of large eggs. In a number of tests at experiment stations
slight differences in the sizes of eggs have been noted with varying
rations and environment, but this can not be attributed to anything
more specific than the general development and vigor of the fowls.
Pullets at the beginning of the laying period lay an egg decidedly
smaller than those produced at a later stage in life. The average
food value of large eggs is slightly greater per pound than that of
small eggs because of a smaller percentage of shell in the former.

The following table gives the sizes of representative classes of eggs.
These figures must not be applied too rigidly, as the eggs of all breeds
and all localities vary. They are given as describing the eggs one may
reasonably expect to find in the class mentioned. It should be borne
in mind that the two classifications given in the table are entirely
independent of each other; the breeds mentioned in the second col-
umn are not the ones which lay the eggs mentioned in the first column,
though they lay eggs of the same size.

TaMe of representative egg sizes.

Geographical classificatiou.

Breed classification.

Eggs from poorest flocks of south-
em dungnillR.

Average Tennessee or Texas eggs . .

Average for the United States as
represented by Kansas, Minne-
sota, and soutnem Illinois.

Southern Iowa's *' two-ounce eggs" .

Average size of eggs produced in

Selected brands of Danish eggs

Games and Hamburgs.

Poor strains of Leghorns

The mixed barnyard fowl of the
western farm, largely of Ply-
mouth Rock origin.

Purebred flocks of American va-
rieties, or egg- farm Leghorns.

American Brahmas and Minor-

Equaled by several pens of Leg-
horns in the Australian laying

per 30-













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Dirty eggs are grouped roughly in three classes — (a) "plain
dirties," those to which soil or dung adheres; (6) stained eggs, those
soiled by contact with damp straw or other material which discolors
the shell (plain dirties when washed usually show this appearance) ;
(c) smeared eggs, those covered with the contents of broken eggs.

For the first two classes the farmer is to blame. The third class
originates all along the route from nest to consumer. The percentage
of dirty eggs varies with the seasoji and weather conditions, being
noticeably increased during rainy weather. About 5 per cent of all
eggs are culled out as "dirties," and these are sold at a loss of at
least 20 per cent. This makes a financial loss of 1 per cent of the
total value of the nation's egg crop.

There is another loss caused by dirty eggs which is fully as serious.
It is the loss due to the fact that in a lot of eggs so handled as to
produce 5 per cent of " dirties " the remainder of the lot will show
enough spotted and stained eggs to give the whole lot an inferior
appearance. The amount of depreciation from this source is difficult
to estimate, but it is undoubtedly as great as the direct loss on those
culled out.


The common trade name for cracked eggs is " checks." " Blind
checks " are those in which the break in the shell is not readily
observable. These are detected with the aid of the candle or by
clicking the eggs together. " Dents " are checks in which the egg
shell is pushed in without rupturing the membrane. " Leakers " have
lost part of the contents and are not only a loss themselves, but
produce smeared eggs.

The loss from mechanical injury varies considerably with the
amount of handling in the process of marketing. A western produce
house collecting from grocers by local freight will record from 4 to 7
per cent of checks. These same eggs in further handling will have
an additional checking of 1 to 3 per cent. Eight per cent of the eggs
from hen to market is probably a fair estimate for broken eggs. The
depreciation of such eggs is greater than that of dirties, being about
25 per cent. This gives a financial loss due to checks of 2 per cent.


The laying of an egg is not analogous to birth in the case of a mam-
mal, and the presence of the male bird is not essential for the laying

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of the egg; hence eggs laid by hens kept away from males are entirely
free from the changes presented under'this head.

That such infertile eggs can not spoil, however, is a mistaken
notion, for they are subject to all the other factors which cause eggs
to spoil. The sale of eggs tested out of incubators has been encour-
aged by the assertion that incubation does not spoil infertile eggs for
food purposes. In practice the idea works great harm. Eggs thrown
out of an incubator will be shrunken and weakened, and many of
them will contain dead germs; that is, the remains of chicks that
have started to develop. If the farmer's wife wishes to use such eggs
at home, where she can examine the broken eggs before using, it is
her own affair; but the sale of incubator eggs as fresh should not be

Fertile eggs immediately after laying can not be distinguished
from infertile eggs, the germ of the chick being microscopic in size.
If the egg is immediately cooled and held at a temperature below
70° F., the germ will not develop. At a temperature of 103° F. the
development of the chick proceeds most rapidly. This development
is about as follows :

Twelve hours' incubation : Examined by a candle such an egg can
not be distinguished from a fresh one. When broken in a saucer the
germ spot, visible upon all eggs, seems somewhat enlarged.

Twenty- four hours: This egg, if not too dark shelled, can be read-
ily detected by th^ professional candler, the germ spot causing the
yolk to appear considerably darker than the yolk of a fresh egg.
Such an egg is called a " heavy egg," or a *' floater." When the egg is
broken, the germ spot appears mottled and about the size of a dime.

Forty-eight hours : By this time the opaque white membrane which
surrounds the germ has spread well over the top of the yolk, and the
egg is quite dark or heavy before the light. Blood appears at about
this period, but is difficult of detection with the candle, unless the
germ dies and the blood ring sticks to the membrane of the egg.

Three days: The candle shows changes in this egg that are ap-
parent even to a novice. An experienced candler will have no dif-
ficulty in seeing the blood ring through the shell. When broken the
blood ring is the prominent feature, and is as large as a nickel. The
yolk behind the membrane has become watery.

Four days : The body of the chick becomes visible to the candler,
and the prominent radiating blood vessels are seen. Upon breaking
the yolk is found to be half covered with the sac containing water.

The developments given above occur at a temperature of 103° F.
As the temperature is lowered the rate of chick development is re-
tarded, but at any temperature above 70° chick development will
proceed far enough to cause serious injury to the quality of the eggs.

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For commercial uses the customary grouping of eggs in regard to
heating is :

1. No heat shown. Can not be told at the candle from fresh eggs.

2. Light floats. First grade that can be separated by candling,
corresponding to about eighteen to twenty-four hours' incubation.
Not objectionable to the average housewife.

3. Heavy floats. This group has no distinction from the preced-
ing, except an exaggeration of the same features. These eggs are
objectionable to the fastidious housewife because of the white and
scummy appearance of the yolk.

4. Blood rings. Eggs in which blood has developed^ extending to
the period when the chick becomes visible.

5. Chicks visible to the candle.

The loss to the egg trade due to heated eggs is probably greater
than that from any other source. The loss varies with the season of
the year and the climate. In New England heat loss may be con-
sidered as in the same class as loss from dirties and checks. In Texas
the egg business from the 15th of June until cool weather in the fall
is practically dead. The southerner eats few eggs at this season, and
shipping out of the State nets the producer such small returns after
allowance for the losses that the farmer considers it hardly worth
while to gather eggs. In the unusually hot season of 1901, through-
out the entire region west of the Mississippi River, hatched chickens
were commonly found in cases of market eggs, and for a time the
shippers did well to net 3 cents a dozen for these eggs.

During the average season the summer egg of the South and
Southwest makes no pretensions to being a sound egg in regard to
heat. Even in the Central West the loss is severe. An average lot
of summer eggs from the Kansas-Nebraska territory would candle up
about as follows :

Candled stock, containing a large proportion of light floats, 80
per cent.

Seconds, containing heavy floats and light blood rings, 15 per cent.

Absolute loss, eggs containing heavy blood rings or chicks, 5 per

Some idea of the financial loss due to heated eggs can be obtained
by estimating what the eggs in the above case are worth when laid
as compared with what they actually bring. The best of the heated
stock referred to above is worth about 5 cents a dozen less than near-
by fresh eggs in the New York market. Supposing the latter to be
25 cents, there is a loss of 5 cents. The value of the seconds, which
will probably be broken as bakers' stock, will not be over 15 cents.
Thus we have 80 per cent at 20 cents a dozen, 15 per cent at 15 cents

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a dozen, and 5 per cent at a total loss. This makes a depreciation of
27 per cent on the original value.

In western eggs a loss due to heating or chick development of ap-
proximately one- fourth of the original value of the crop is sustained
during the heated season.

The loss attributable to this element of egg deterioration is esti-
mated at fully 5 per cent of the annual valuation of the egg crop of
the country. In the East the loss would be less, while in the South
it would be much greater.

The responsibility for heated eggs is almost wholly with the
farmer, although the rural buyer and the freight handler are in no
wise innocent.


The eggshell is porous so that the developing chick may obtain air.
This exposes the moist contents to the drying influence of the atmos-
phere, and evaporation takes place constantly. It is increased by
warm temperatures, by dry air, and by currents of air striking
the egg.

When the egg is formed within the hen the contents fill the shell
completely. As the egg cools the contents shrink, and the two
layers of membrane separate in the large end of the egg, causing the
appearance of the bubble or air cell. Evaporation of water from the
egg further shrinks the contents and increases the size of the air
cell. The size of the air cell is commonly taken as a guide to the
freshness of the egg, but when we consider that with the same
humidity evaporation would take place much faster on a hot July
day than on a frosty November morniiig, we see that the extent of
evaporation from the egg proves little regarding the actual age.
Even as a measure of evaporation the size of the air cell may be de-
ceptive, for when an egg with an air cell of considerable size is
roughly handled the membrane splits down the side of the egg and
gives the air cell the appearance of being larger than it really is.
Still rougher handling of shrunken eggs may cause the rupture of the
inner membrane, allowing the air to escape into the contents of the
egg. This causes a so-called " watery " or " frothy " egg. The quality
is in no wise injured by the mechanical mishap, but eggs so ruptured
are usually discriminated against in candling.

In this connection it might be well to discuss the subject of " white
strength," by which is meant the stiffness or viscosity of the egg
white. The white of an egg is a limpid liquid, but in the egg of
good quality that portion immediately surrounding the yolk appears
to be in a semisolid mass. The cause of this appearance is the pres-

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ence of kn invisible network of fibrous material. By age and mechan-
ical disturbance this network is gradually broken down and the liquid
white separates out. Such a weak and watery white is usually asso-
ciated with shrunken eggs. These eggs will not stand, up well or
whip into a firm froth, and are discriminated against by dealers.
The weakness of the yolk membranes also increases with age, and is
objectionable because the breakage of the yolk is unsightly and spoils
the egg for poaching.

The shrunken egg is most abundant in the fall, when the rising
prices tempt the farmer and groceryman to hold the eggs. In fact,
this holding is so prevalent that from August to December fresh
eggs are the exception rather than the rule. While attention has been
called to evaporation as the most pronounced fault of fall eggs, losses
from other causes are greatly increased by the holding of eggs. If
the eggs are held in a warm place, heat and shrinkage will cause the
greatest loss; if held in a cellar, rots, mold, and bad odors will be
the cause of a lowered price.

The loss in the egg business due to holding is perhaps least under-
stood and appreciated by those outside the trade. This is due to the
fact that the shrunken egg is not so repulsive as the rotten or heated
egg. But the inferiority of the shrunken egg is sp well appreciated
by the consumer that high-class dealers find it impossible to use them
without ruining their trade. This causes shrunken eggs to be con-
stantly sent into the cheaper channels of consumption, with the result
that all lower grades of eggs are a drug on the market in the fall of
the year.

In the northern and eastern sections the farm and store holding of
eggs is probably greater than it is in the South and West, and in the
former sections the loss from this cause exceeds that from heated
eggs. Taken the country over, the loss due to the holding for higher
prices is probably about equal to the loss due to chick development.


In the classes of spoiled eggs which we have thus far discussed
the proverbial rotten egg has not been considered. The term " rot "
in the egg trade is applied in any case where an egg is absolutely
unfit for food purposes. In this discussion the term "rotten egg"
will be confined to the egg which contains a growth of bacteria.

The egg when laid is usually germ free, and if properly cared for
will remain so. The eggshell itself is not germ proof, for the pores
that admit the air for the chick to breathe are large enough to admit
all forms of bacteria, but the membrane beneath the shell is germ
proof as long as it remains dry. This membrane is composed of
fibers crisscrossed in every direction. The dried spore of a bacte-

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rium falling on this membrane would lodge in the sam^ matin^l* as
would the body of a dead mouse upon a pile of hay ; but let the right
conditions of moisture and warmth be present to call the germ into
activity, the membrane will be no more a barrier than the hay would
be to a live mouse.

The exterior of an egg is a lodging place for bacteria and bacterial
spores of all kinds, and once an egg becomes damp or is broken de-
composition speedily follows. As in other products, heat favors the
growth of bacteria and sufficient cold will prevent it. Unless there is
moisture on the surface of the egg bacteria can not enter, and there-
fore dampness of the eggshell, practically speaking, is to be consid-
ered the cause of rotten eggs. Damp membranes may come from
water externally applied, from the " sweating " of eggs coming out
of cold storage, or from preventing evaporation to such an extent that
the internal moisture of the egg thoroughly soaks the membrane.
The latter occurs in damp cellars or when eggs are covered with some
impervious material. Rotten eggs may be of different kinds, accord-
ing to the species of germ that causes the decomposition. The spe-
cific kinds of egg-rotting bacteria have not been worked out, but the
following three groups of bacterially infected eggs are readily dis-
tinguishable in the practical work of egg handling : .

1. Black rota. — It is probable that many different species of bac-
teria cause this form of rotten eggs. The prominent, feature is the
formation of hydrogen-sulphid gas, which blackens the contents of
the egg, giving the characteristic rotten egg smell and sometimes
causing the equally well-known explosion.

2. Sour eggs or white rots. — These eggs have a characteristic sour
smell. The contents become watery, the yolk and the white mixed,
and the whole egg offensive to both eye and nose.

3. The spot rot. — In this case the bacterial growth has not contami-
nated the entire egg, but has remained near the point of entrance.
Such eggs are readily picked out with the candle, and when broken
show lumpy adhesions on the inside of the shell. These lumps
are of various colors and appearances. It is probable that spot rots
are caused as much by mold as by bacteria, but for practical purposes
the distinction is immaterial.

In practice it is impossible to separate rotten from partly hatched
eggs, for the reason that in the typical nest of spoiled eggs found
around the farm both causes have been at work. Dead chicks will
not necessarily cause the eggs to decay, but many such eggs do be-
come contaminated by bacteria before they reach the candler, and
hence show complications.

The loss of eggs that are actually rotten is not as great as one might
suppose. Perhaps 1 or 2 per cent of the year's output actually rots,

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but the expense of the candling and the lowering of the value of the
egg crop are severe losses for which the rotten eggs are to blame.
The responsibility for decayed eggs is to be shared between the
farmer who allows hens to lay in the weeds or under the barn, and
the dealer who holds the eggs in damp cellars or poorly managed
storage rooms awaiting higher prices.


Moldy or musty eggs are caused by the accidental wetting of cases
or bj^ storage in very damp cellars or ice houses. The moldy egg
is also frequently affected with spot rot. In the musty egg proper
the egg meat is free from organisms, but has been tainted by the
odor of the moldy growth upon the eggshell or the packing materials.


The absorption of odors is the most baffling of all causes of bad
eggs. Here the candler, so expert in other points, is usually help-
less. Eggs, by storage in musty cellars or in rooms with citrus
fruit, vegetables, fish, or cheese, may become so badly flavored as
to be seriously objected to by a fancy trade, and yet there is no
means of detecting the trouble without destroying the egg. Such
eggs occur most frequently among the held stock of the fall season.

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Online LibraryUnited States. Bureau of Animal IndustryCircular (United States. Bureau of Animal Industry). no. 138-150a, 1909-11 → online text (page 5 of 21)