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Candling Appearance of Eggs and their Thick White Percentage
quality. Among the important factors found by
him to affect candling appearance were : yolk
colour as influencing yolk shadow, position of the
yolk, distribution of thick and thin white and
cloudiness of albumen. In addition to the above
were the changes in the size of the air space, the
defects of the air space, the mottling of the shell
and the shell texture. Tinted, thick and spotted
shells also interfere with candling appearance.
Schroeder [1933] also observed that candling was
not a sufficiently accurate index of actual interior
quality He pointed out the influence of yolk
colour on yolk shadow, the impossibility of finding
out flavour by candling and also the general
inaccuracy in classifying eggs as 'watery whites'
for reasons such as the presence of bubbly air cells.
Coles [1940] mentioned the effect of misplaced
chalaza or ruptured thick white layer on yolk
visibility. How changes in temperature or pH
may affect the candling appearance of eggs has been
studied by Almquist, Givens and Klose [1934].
They noticed that the transmission of light varied
in the different layers of egg albumen and that
this was correlated with the percentage of mucin
in the white. The physical condition of the mucin
was affected by changes in the temperature and
pH. They found that the changes in the trans-
mission of light due to these factors caused differ-
ences in the candling appearance of eggs which
were not necessarily correlated with the changes
in their interior quality. In spite of these several
drawbacks, Almquist [1933] holds that 'in view
of the number of widely differing factors that
contribute to the quality of an egg, it appears
extremely unlikely that any grading method can
be devised which will possess as much versatility,
accuracy and speed as the candling method '.
The following investigation was undertaken to
find out the relationship of candling appearance
to actual interior quality.
PROCEDURE
Day-old eggs from birds of the Institute flock
consisting of White Leghorns, Rhode Island Reds
and desis, which were fed, housed and managed
under standard conditions, were used for the
experiment. The eggs were candled and divided
into two arbitrary grades according to their
candling appearance. The mobility of the yolk
and the intensity of the yolk shadow were the main
considerations according to which eggs were graded
for their interior quality. Those with limited
yolk movement and dim yolk shadow were classed
as grade I, and the rest, with free and rapid
movement of the yolk and a comparatively darker
yolk shadow, were classed as grade II. In assign
ing the candling grade, egg faults such as mean
spots, blood, cracks, defective air cells, etc
when present were ignored. The candling was
carried out in a darkened room with the aid of at
Ovolux egg candler (Plate XI, fig. 1) fitted with
a 25 watt clear glass bulb. After candling, all the
eggs were broken out and the actual interior
quality determined by measuring the percentage
thick white. This estimation was carried out
(Plate XI, fig. 2) by the sieve method of Holst and
Almquist [1931] as described by Macdonald and
Krishnan [1942].
During the course of the experiment, which
lasted from 1 March to 31 July, 1940, 542 white
Leghorn, 576 Rhode Island Red and 750 desi
eggs were examined.
EXPERIMENTAL RESULTS
The frequency distributions of the percentage
thick white of eggs of different breeds for the two
candling grades and their statistical significance
are given in Table I and the Chart. From Table I
it is seen that, out of the 1868 eggs examined during
the experiment, from all breeds combined, 1291
(i.e. 69.11 per cent) were classed on candling as
grade I. The proportion of eggs candled as grade
I from the three different breeds, White Leghorns,
Rhode Island Reds and desis, were 67.16, 78.65
and 63.20 per cent respectively. Hence, except
in the case of the Rhode Island Reds, about
two-thirds of all the eggs candled were assigned to
grade I. Among the Rhodes, however, the pro-
portion of eggs assigned to this grade was a little
more than three-quarters of the total number
tested.
An examination of Fig. 1 shows
that the frequency distribution curves of the
different breeds are more or less the same in both
the grades. It also appears that there are no
outstanding differences between the slopes of the
curves of the two grades in the same breed. The
curves for the Rhode Island Reds have a tendency
to shift more towards the side of the lower thick
white percentages, while the others tend to have
a greater spread in the region of the higher thick
albumen figures. These tendencies are brought
out by the frequency distribution figures presented
in Table II. In this table the eggs of the different
breeds, in each grade, have been classified into
three main groups—poor, average and high
quality—according to their percentage thick
white. The figures show that, while in both grades
of all the breeds the eggs of average quality
constitute roughly half the total, the proportions
of those of poor and high quality are comparatively
small.