mineral. The composition of the yolk is about 49.5 per cent water; 33.3
per cent fats, including lecithin and cholesterol; 15.7 per cent proteins; and
1.0 per cent minerals.
Color of shell and yolk.- The color of the shell is determined by
inheritance, certain breeds laying white, others brown-colored shells. The
Barnaveldters lay eggs with nearly chocolate-brown shells.
The coloring matter of the yolk, according to Palmer, Mattikow, and
others is xanthophyll, with a small proportion of a carotene-like pigment.
The intensity of the yolk color is determined by the amount of xanthophyll
in the food of the hen. The color of the yolk may vary from a very pale,
almost white yolk, through deeper yellows to orange and finally a deep-
red-orange. Some feeds may produce red-colored yolks. Some attempts
have been made to work out color charts, giving each shade a number ; but
most of these are only tentative. It is an advantage for bakers and mayon-
naise manufacturers to obtain yolks of uniform color to insure uniformity
326 EGG COOKERY
of color of their products. A small number of manufacturers at present do
specify the color of the egg yolks when they place their contract for them.
Reaction of eggs. 1 he egg white is alkaline. Sharp found that the
pH of the white varies from 7.6 to 9.7, whereas the yolk of fresh eggs
averages pH 6.0 or slightly lower. The pH of both the white and yolk
increases with age because of the loss of carbon dioxide. Sharp and Powell
state that since the loss of some carbon dioxide cannot be prevented before
the pH is taken, that a pH of 7.6 is probably too high for freshly laid eggs.
With further loss of carbon dioxide the pH may increase to 9.5. Then,
probably owing to break down of some of the egg protein, the pH decreases.
The />H of the yolk may reach 6.8, but changes more gradually than that
of the white. When the whole egg is beaten so that the white and yolk are
mixed, a pH. intermediate between that of the white and yolk is obtained.
Egg Quality
The term "quality" as applied to eggs refers ultimately to their desir-
ability for human consumption. When an egg deteriorates its cooking
qualities are altered. It is commonly accepted that an egg of high quality
is better for poaching, boiling, and frying than one of inferior quality. At
present, for trade use, eggs of quality are defined as those having a rela-
tively high percentage of thick to thin white, and a high percentage of yolk
solids. These eggs, when broken on a flat surface, do not tend to flatten
out as quickly nor to so great an extent as eggs of poorer quality. See
Fig. 32.
Page 264
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mineral. The composition of the yolk is about 49.5 per cent water; 33.3
per cent fats, including lecithin and cholesterol; 15.7 per cent proteins; and
1.0 per cent minerals.
Color of shell and yolk.- The color of the shell is determined by
inheritance, certain breeds laying white, others brown-colored shells. The
Barnaveldters lay eggs with nearly chocolate-brown shells.
The coloring matter of the yolk, according to Palmer, Mattikow, and
others is xanthophyll, with a small proportion of a carotene-like pigment.
The intensity of the yolk color is determined by the amount of xanthophyll
in the food of the hen. The color of the yolk may vary from a very pale,
almost white yolk, through deeper yellows to orange and finally a deep-
red-orange. Some feeds may produce red-colored yolks. Some attempts
have been made to work out color charts, giving each shade a number ; but
most of these are only tentative. It is an advantage for bakers and mayon-
naise manufacturers to obtain yolks of uniform color to insure uniformity
326 EGG COOKERY
of color of their products. A small number of manufacturers at present do
specify the color of the egg yolks when they place their contract for them.
Reaction of eggs. 1 he egg white is alkaline. Sharp found that the
pH of the white varies from 7.6 to 9.7, whereas the yolk of fresh eggs
averages pH 6.0 or slightly lower. The pH of both the white and yolk
increases with age because of the loss of carbon dioxide. Sharp and Powell
state that since the loss of some carbon dioxide cannot be prevented before
the pH is taken, that a pH of 7.6 is probably too high for freshly laid eggs.
With further loss of carbon dioxide the pH may increase to 9.5. Then,
probably owing to break down of some of the egg protein, the pH decreases.
The />H of the yolk may reach 6.8, but changes more gradually than that
of the white. When the whole egg is beaten so that the white and yolk are
mixed, a pH. intermediate between that of the white and yolk is obtained.
Egg Quality
The term "quality" as applied to eggs refers ultimately to their desir-
ability for human consumption. When an egg deteriorates its cooking
qualities are altered. It is commonly accepted that an egg of high quality
is better for poaching, boiling, and frying than one of inferior quality. At
present, for trade use, eggs of quality are defined as those having a rela-
tively high percentage of thick to thin white, and a high percentage of yolk
solids. These eggs, when broken on a flat surface, do not tend to flatten
out as quickly nor to so great an extent as eggs of poorer quality. See
Fig. 32.