Vitelline membrane strength. Another method for determining quality is
to measure the strength of the vitelline membrane. The average thickness
of this membrane has been reported to be about 64/100,000 of an inch. In
a fresh egg its bursting strength is about 0.065 pounds per square inch.
With deterioration the strength of the membrane decreases and the yolk
breaks easily when the strength has fallen to a little over half this value.
Factors affecting quality of eggs. Fresh-laid eggs vary in propor-
tions and viscosity of the thin and thick white. The yolk membrane also
varies in strength. These variations are probably due to feed, the season
of the year, the period of the laying cycle, and individual characteristics of
the hen. It has already been mentioned that Wilcke found that the rations
did not influence the viscosity of the egg in his investigations, but he states
his work does not rule out this factor. Lorenz and Almquist report that
the percentage of firm white is lowered by higher air temperature during
the hours immediately after the egg is laid, resulting in an apparent seasonal
variation in internal egg quality. The poorer quality of eggs obtained during
summer months is attributed to the higher temperature during this season.
The finest quality eggs are claimed to be those laid in the spring, which
coincides with the time of greatest production.
328 EGG COOKERY
Preservation and deterioration of eggs. Sharp states that "as soon
as the egg leaves the hen it begins to decline in interior quality and the best
we can hope to do is to retard these changes as much as possible. They
cannot be stopped, they can only be retarded. An egg a week old may have
deteriorated more in quality than an egg properly cared for which is a
year old."
Eggs are preserved by (1) storing at low temperatures, (2) by freezing,
(3) by drying, and (4) by oil dipping.
Storing at low temperatures. In commercial storage the temperature,
humidity, and air currents are controlled, the last to prevent mold growth.
A high moisture content in the storage air lessens the amount of the water
evaporated from the egg, but encourages mold growth. The storage tem-
perature is usually maintained at 29° to 30°F. In addition chemical control
of the atmosphere is frequently practised in the storage rooms. Stewart and
Sharp state that at 30°F., if 0.6 per cent carbon dioxide is used, the /)H
of the egg white will be maintained at 8.0 to 8.1. If the concentration of
carbon dioxide is too high, the white becomes turbid, but loses this turbidity
after loss of some carbon dioxide from the egg on breaking.
Most of the eggs placed in low temperature storage are stored during
March, April, May, and June. More than half of the annual supply of
eggs is laid during these four months. Withdrawal of eggs from storage
usually begins in August, reaches its peak about November, and the supply
is generally exhausted by January.
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Vitelline membrane strength. Another method for determining quality is
to measure the strength of the vitelline membrane. The average thickness
of this membrane has been reported to be about 64/100,000 of an inch. In
a fresh egg its bursting strength is about 0.065 pounds per square inch.
With deterioration the strength of the membrane decreases and the yolk
breaks easily when the strength has fallen to a little over half this value.
Factors affecting quality of eggs. Fresh-laid eggs vary in propor-
tions and viscosity of the thin and thick white. The yolk membrane also
varies in strength. These variations are probably due to feed, the season
of the year, the period of the laying cycle, and individual characteristics of
the hen. It has already been mentioned that Wilcke found that the rations
did not influence the viscosity of the egg in his investigations, but he states
his work does not rule out this factor. Lorenz and Almquist report that
the percentage of firm white is lowered by higher air temperature during
the hours immediately after the egg is laid, resulting in an apparent seasonal
variation in internal egg quality. The poorer quality of eggs obtained during
summer months is attributed to the higher temperature during this season.
The finest quality eggs are claimed to be those laid in the spring, which
coincides with the time of greatest production.
328 EGG COOKERY
Preservation and deterioration of eggs. Sharp states that "as soon
as the egg leaves the hen it begins to decline in interior quality and the best
we can hope to do is to retard these changes as much as possible. They
cannot be stopped, they can only be retarded. An egg a week old may have
deteriorated more in quality than an egg properly cared for which is a
year old."
Eggs are preserved by (1) storing at low temperatures, (2) by freezing,
(3) by drying, and (4) by oil dipping.
Storing at low temperatures. In commercial storage the temperature,
humidity, and air currents are controlled, the last to prevent mold growth.
A high moisture content in the storage air lessens the amount of the water
evaporated from the egg, but encourages mold growth. The storage tem-
perature is usually maintained at 29° to 30°F. In addition chemical control
of the atmosphere is frequently practised in the storage rooms. Stewart and
Sharp state that at 30°F., if 0.6 per cent carbon dioxide is used, the /)H
of the egg white will be maintained at 8.0 to 8.1. If the concentration of
carbon dioxide is too high, the white becomes turbid, but loses this turbidity
after loss of some carbon dioxide from the egg on breaking.
Most of the eggs placed in low temperature storage are stored during
March, April, May, and June. More than half of the annual supply of
eggs is laid during these four months. Withdrawal of eggs from storage
usually begins in August, reaches its peak about November, and the supply
is generally exhausted by January.