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The Measurement of Freshness of Unbroken Eggs
T h e Measurement of Freshness of Unbroken Eggs R.
H.
CAER
Department of Agricultural Chemistry, Purdue University Agricultural Experiment Station, Lafayette, Indiana (Received for publication August 15, 1938)
T
HERE has been an unusual interest in the freshness of eggs on the part of consumers in recent years. This awakening may be caused by a wave of food consciousness in general but more probably by the publicity given to possible ways of preserving the freshness for a longer period, such as oiling and use of oil wrappers, carbon dioxide treatments, cold storage temperatures and humidity, water glass solutions, etc.—all of which leads the consumer to ponder over the freshness of breakfast eggs. This study was made to furnish a means of determining the freshness of eggs by showing internal changes in the egg before it is broken. Candling of large supplies of eggs appears to be the best way to grade the carloads which must be handled, but it is too indefinite for the research worker who is concerned with the freshness and flavor of each individual egg. Among the methods noted in the literature for determining the freshness of unbroken eggs are: the variability of shell porosity with age as noted by Almquist and Hoist (1931); the transmission of light through egg shell reported by Givens, Almquist and Stokstad (1935); the movement of ice water through the membranes of fresh but not of stored or stale eggs;1 and the specific gravity of eggs (Curtis, 1911). Progress in determining the condition of the inside of the unbroken egg has been slow and little is known about market eggs until they are broken open. Even then 1
Unpublished data.
there is often much room for doubt as to the quality of the eggs. Time is very important in the taste value of an egg, as each day, with some few exceptions, the yolk gets heavier, the white thinner, and the taste becomes less pleasing. There are many interpretations involved in the term "freshness," but the three which are most evident may be noted as follows: first, the thick white becomes liquid rather rapidly; second, the movement of water from the white into the yolk weakens the membranes around the yolk and makes it tend to flatten out or even break when the egg is opened; and third, the true thick albumen breaks down from loss of water and carbon dioxide. It is the loss of all of these which is small (0.5-0.7 percent per day), but hard to stop, which furnishes a good clue to the age of the egg. Since the proteins which compose the white and yolk of eggs are combined with so much water, especially the white, and since they are partly stabilized when fresh with enough carbon dioxide to make the white rather firm it can be seen that the escape of carbon dioxide from day to day together with the contact with the basic calcium carbonate of the shell will rapidly raise the pH and make a more liquid albumen. EXPERIMENTAL PROCEDURE
It would seem on first thought that the small changes in shrinkage, which eggs undergo daily, are too small to be of importance in evaluating freshness. This loss amounts to only about 0.10 grams per day
[22S]
226
R. H. CARR
per egg and is nearly the same for all eggs regardless of age, from floaters to the best of fresh eggs. Old eggs will float on water while fresh eggs will sink. Approximately a six gram load is required to prevent a fresh egg from sinking. Hence there is a range of only six grams involved, which
grams for the 100 divisions. The dial handle was grooved and attached to the spring coil with a fine wire, thus making it possible to measure small changes with considerable accuracy. The dial reading has been designated as the "Jolly" egg number, after the Munich physicist by that name. The buoyancy weight is obtained by multiplying the dial reading by 0.08 grams. As an example egg No. 50 in Table 1 had a Jolly number of 57 and a buoyancy weight of 4.56 grams (57 x .08 = 4.56).
4 A. Drawing of Jolly egg apparatus.
becomes very important in measuring egg quality and age. An accurate instrument is required to determine each small deviation from the normal fresh or standard egg. The Jolly balance was used to determine this difference in buoyancy. A modified instrument constructed in the laboratory was used (Figure 1). A radio dial was employed to measure the elongation of the spring from which buoyancy weight was calculated. Each division on the dial was found to be equivalent to 0.08 grams or 8
B. Photograph of apparatus as used. EXPERIMENTAL RESULTS
In order to standardize the Jolly balance for eggs it was necessary to find out first what is to be expected in the variations in buoyant effect among day old eggs and to
MEASUREMENT OF FRESHNESS OF UNBROKEN EGGS
find out so far as possible by analysis what causes each of these variations. Fresh eggs were collected from the University Farm and divided in three main groups according to weight. Group A included eggs weighing 57 grams or more, group B eggs weighing 47 to 57 grams and group C eggs weighing less than 47 grams. The weight of the egg, yolk, albumen, and shell and membrane together with the Jolly number and buoyancy weight were determined. The data are given in Table 1. It will be observed from this table that the yolk solid is the heavy portion of the edible part of an egg and usually has more than 50 percent of its weight solid material. It will be noted also that the fresh weights of eggs 45 and 52 indicate heavy yolks, but the small weights of their dried solids show they were watery and were easily detected by their Jolly number and buoyancy weight. The white of an egg consists of three main parts—an outer thin white, a middle layer of jelly white, together with a layer next to the yolk and continuous with the chalazae. It is probably this thick white rather than the total weight of white in an egg that is the most important factor in determining freshness by the Jolly number. The thick white is notable for its high content of the glucoprotein-mucin which is characterized by its ability to swell in water. It was shown by Moran (1937) that at a pH greater than 6 the swelling of mucin particles was so great and their density so near to that of water that it was impossible to separate them in bulk from the solution. He noted also that the decrease in volume and gel strength of the thick white during storage is caused by the chemical breakdown of the mucin and to the shrinkage of the gel framework. When this collapse of the gel has occurred through change in carbon dioxide content, enzyme action, or other reasons the original volume of the thick white is not regained; hence the big shrinkage of this large
227
mass of gel in the thick white, with the production of an airpocket is an outstanding result of storing eggs and this can be detected by the low Jolly number of an old eggThe weight of the shell should make a difference in the Jolly number if it were anything like that of number 58, Table 1, which has a Jolly number of only 31 (buoyancy weight = 2.48 grams) but, of course, this thin crust of a shell and most other shells of this thin chalky structure are easily evident and can be avoided. Egg 45 had a small weight of shell and a very low percentage of dried yolk also; hence a low Jolly number. If it is the amount of albumen that is most desirable in buying eggs for special uses, the small eggs may be very desirable as those noted in Table 1 have relatively three percent more albumen to yolks than the larger egg. In a recent article Olsson (1934) noted that a high correlation was found between the specific gravity and the percentage of shell weight of the total weight of the egg— indicating specific gravity was a good measure of the percentage of shell. The specific gravity of yolk was found to average 1.032, the albumen 1.036, and the shell 2.325. It would appear from Table 1 that shell, yolk, and albumen have to be considered in the Jolly number interpretation. Thus eggs generally may be grouped as A, B, or C on the basis of their dried shell and membrane as follows: Group A—57 gram egg or more, the shell-membrane should weigh over 5 grams; Group B—eggs over 47 grams, shellmembrane should weigh over 4 grams; whereas Group C—eggs under 47 grams weight should average over 3 grams. The data indicate that fresh eggs weighing 57 grams or above will have a Jolly number of 63 or more, those weighing 47 to 57 grams will have a Jolly number of over 50, and those weighing less than 47
228
R. H. CARR TABLE 1.— Data
Egg Egg NumWeight ber
obtained on fresh eggs of different weights
Yolk
Albumen
Fresh Weight
Dry Weight
Gms.
Gms.
Gms.
67 66 47 59 63 70 49 56 45 60 57 65 Average
*68.61 67.85 =64.47 64.31 "63.88 61.95 60.27 "60.16 "59.79 "59.93 58.36 '57.82
19.607 23.551 16.851 20.250 18.942 20.043 19.054 19.829 21.027 18.211 16.588 18.156
Percent Group A 9.880 50 12.551 52 8.821 52 10.367 51 9.699 51 10.998 55 11.311 59 11.989 60 9.445 45 9.429 52 8.611 52 9.110 50
62.28
19.342
10.184
52 54 46 64 53 51 55 50 48 71 Average
"56.51 "56.66 "54.08 "54.43 53.17 51.21 "51.89 50.87 49.72 47.00
22.352 17.077 15.888 15.437 17.443 17.850 16.978 17.807 16.251 18.245
52.55
17.533
61 62 72 73 69 Average
"46.55 "46.87 44.63 "44.07 32.10
24 25 58
Solids
Fresh Weight
Dry Weight
Gms.
Gms.
Shell and Membrane Solids
Fresh Dry SolWeight Weight ids Gms.
Percent
5.956 5.696 5.423 5.463 4.935 5.832 5.819 5.173 3.653 5.057 5.228 6.156
78 70 77 77 69 69 80 76 75 73 73 87
66 67 55 66 63 62 68 74 46 66 63 62
5.28 5.36 4.40 5.28 5.04 4.96 5.44 5.92 3.68 5.28 5.04 4.96
5.366
75
63
5.05
3.915 4.984 4.706 4.907 4.737 4.315 4.271 5.042 4.908 4.660
65 75 79 69 75 63 79 73 72
—
49 61 60 55 59 49 54 57 56 51
3.92 4.88 4.80 4.40 4.72 3.92 4.32 4.56 4.48 4.08
4.644
72
55
4.41
15.197 15.875 11.460 12.215 9.128
57 28.275 3.267 11.3 6.455 Group C (weight, below 47 grams) 7.291 48 25.491 3.032 11.9 5.640 8.506 54 25.071 2.617 10.4 5.676 5.891 55 27.827 3.450 12.4 5.022 54 25.849 3.369 6.638 — 5.882 44 18.076 2.463 13.6 4.769 4.048
3.682 3.822 4.266 4.823 3.753
65 67 85 82 79
47 47 47 53 42
3.76 3.76 3.76 4.24 3.36
42.84
12.771
6.475
4.069
76
47
3.78
"30.53 "17.53 *42.58
0.0 trace 14.581
0.0
46
38 29 31
3.04 2.32 2.48
*—largest egg. B —flat side. °—no yolk—long.
(weight, 41.334 36.234 40.614 36.471 37.471 33.132 33.925 33.515 33.837 34.789 34.155 32.332
PerGms. cent 57 grams or above) 4.776 11.6 7.564 3.692 9.9 8.064 4.224 10.4 7.000 3.471 10.5 6.942 4.895 12.8 7.089 3.652 11.0 8.422 4.071 12.0 7.291 3.754 11.2 6.815 — — 4.829 4.075 11.7 6.686 3.911 11.5 7.178 3.751 11.6 7.092
Jolly BuoyNo. ancy Weight
52 35.651 Group B (weight, 51 28.178 11.263 10.468 61 32.798 8.939 56 31.400 8.167 53 31.645 10.346 59 29.283 8.895 50 26.410 9.976 59 28.661 10.287 58 26.027 9.238 57 26.050 12.032 66 22.294
4.025 11.3 7.081 47 to 57 grams) 3.381 12.0 6.038 3.345 10.2 6.685 3.642 11.6 5.937 4.064 12.8 7.044 3.337 11.4 6.339 2.468 9.5 6.850 3.462 12.0 5.431 2.837 10.9 6.939 2.865 11.0 6.827
—
—
—
9.961
7.477
51
51
24.463 Freak 24.635 14.428 23.163
2.986 Eggs 5.896 2.258 2.883
*—no shell—crust. n —very long—thin.
grams a Jolly number of less than 50. Pullet eggs, eggs without shell and freak eggs will not conform to the above specifications. Table 2 shows the changes that take place in the weight of eggs stored under different conditions. It will be noted that,
12.1
5.398
23.9 15.7 12.5
3.105 3.953
1.831
Gms.
-round—hard to break, -brown egg.
however fresh an egg may have been, it is hard to keep it from losing weight even when it is held in cold storage or wrapped in aluminum foil or oiled. The daily losses in weight given in Table 2 call attention to how regular the loss is and how difficult it is to stop loss in weight and especially how
229
MEASUREMENT OF F R E S H N E S S O F U N B R O K E N EGGS
TABLE 2.—Loss of weight in eggs on storage under different conditions Egg Weight Egg Number
Fresh Gms.
10 Days Later Gms.
25 Days Later
37 Days Later
Gms.
Gms.
Total Loss in Weight
Average Daily Loss in Weight
Gms.
Gms.
Jolly Number Fresh
37 Days Later
Eggs wrapped in aluminum foil—-Stored at 25-27°C. 1 2 3 4
57.899 47.505 62.058 57.609
57.439 47.250 61.688 57.214
57.349 46.682 61.024 56.559
56.416 46.177 60.147 55.882
Average
1.483 1.328 1.911 1.727
0.040 0.036 0.052 0.047
59 49 65 60
40 32 40 39
1.612
0.044
58
38
0.948 1.203 1.187 1.198 1.272
0.026 0.033 0.032 0.032 0.034
57 53 53 59 61
45 38 39 43 46
1.162
0.031
57
42
Fresh
30 Days Later
Eggs in Refrigerator—Stored at 4-5°C. 5 6 7 8 9
55.794 50.563 50.833 56.906 59.495
55.546 50.300 50.479 56.555 59.000
55.283 50.018 50.203 56.268 58.813
Average
54.846 49.360 49.646 55.708 58.223
Eggs Oiled—Machine Oil—Stored at 25-27°C.
10 11 12 13
Fresh
30 Days Later
62.786 54.329 57.400 54.147
62.003 53.870 56.590 53.546
Average
0.783 0.459 0.810 0.601
0.026 0.015 0.027 0.020
63 57 59 56
52 51 48 47
0.663
0.022
59
50
Fresh
14 Days Later
Uncovered and Untreated Eggs—Stored at 25-27°C.
14 15 16 17
Fresh
8 Days Later
14 Days Later
57.240 61.482 53.134 54.337
56.364 60.888 52.106 52.892
55.553 60.353 51.166 51.581
Average
an individual egg is compared to other eggs treated in the same way. It will be noted from Table 2 that although the daily loss in shrinkage may seem small, it is quite constant and hard to stop even in the case of oiled eggs. Thus, because of the regular loss, it is possible by means of the Jolly number to determine the approximate age of eggs, as normal fresh eggs will
1.687 1.129 1.968 2.756
0.121 0.081 0.141 0.197
59 64 55 56
37 49 30 12
1.885
0.135
59
34
have a Jolly number over SO and if below 50 the untreated eggs at room temperature will lose 0.10 gram per day or 0.70 gram per week until they will reach 0 grams (floaters). It was believed that the thickness of the egg white which is so characteristic of fresh eggs had some bearing on the Jolly number. Hence, using wire screen, number 20 mesh,
230
R. H. CARR
wire number 27, tests were made on the fresh eggs studied in Table 1, as well as on other commercial eggs. This consisted of breaking the egg on a screen resting on a beaker, and removing the yolk with the aid of a watch glass or retaining it in the half shell. After the drip had quit the volume of liquid and the thick white on the screen were measured. The data are given in Table 3. It was found that the volume of thick TABLE 3.—Effect
of thickness of albumen on the Jolly number
Egg Thick Thin Num- Albu- Albuber men men
Thick Albumen
Buoyancy Weight
Jolly Number
46 47 48 49 50
cc. 17 22 14 21 12
cc. 12 16 10 10 11
Percent 58.6 57.9 58.3 67.7 52.2
Gms. 4.80 4.40 4.48 5.48 4.56
60 55 56 56 57
51 52 53 54 55 56
23 17 23 23 18 20
1 8 4 7 10 12
95.8 68.0 85.2 76.7 64.3 62.5
3.92" 3.92* 4.80 4.89 4.30 5.82
49 49 • 60 61 53 73
x
Small yolks.
and thin albumen was not important in affecting the Jolly number, as both the stiff and watery white has about the same solid content. It will be noted in Table 3 that the percentage of thick white in fresh eggs varies from 52.1 to 95.8 of total white but this did not materially affect the Jolly number. Sharp and Powell (1931) emphasize the usefulness of pH as a guide to the quality of eggs, noting that the white changes from about pH 7.6 to 9.25 in two days at 37°C, in five days at 16°C, and 10 days at 2°C. This is due to the rapid loss of carbon dioxide in a short time even when eggs are cold. Erikson et al. (1932) stress the value of pH for testing freshness of eggs. Healy and Peter (1925) explain the changes in
the pH of the albumen as due to a disturbance in the bicarbonate buffer system. It has been our observation that all eggs after as little as 48 hours will give a red color when phenolphthalein is added to the shell and membrane. It appears to be reasonable that when the carbon dioxide which is dissolved in the white is released and comes in contact with the calcium carbonate of the shell to form bicarbonates the alkaline reaction produced would hasten the breakdown of the albumen. During the progress of this study, it has been a matter of personal interest to purchase eggs which were represented to be fresh, and later to test them for the Jolly number. It was often found that the eggs were from mixed lots, having in one-half dozen three or four with Jolly numbers over 60, indicating that they were fresh and the remainder having low numbers of 25 to 35, which indicated old eggs. After opening the eggs it was found that the Jolly number indicated the true condition of the egg. Thus by means of the Jolly balance it is possible to determine easily the relative freshness of the unbroken egg. SUMMARY
1. The Jolly balance furnishes a means of checking up on the probable freshness of eggs before they are opened. 2. By using many fresh, day old eggs as a standard it was found that the Jolly number was over 50 for eggs weighing over 47 grams and 63 or more for those over 57 grams. 3. The Jolly number of the normal fresh egg ranging from 50 to 70 grams, regardless of the shape, is dependent on the dry weight of the yolk, which is over half solid, and the shell and membrane, which is about 75 percent solid. The large bag of thick egg white is important in its effect on the Jolly number, as it is largely re-
MEASUREMENT OF FRESHNESS OF UNBROKEN EGGS
sponsible for the air pocket produced when the thick white collapses and loses its gel structure. 4. It is convenient to divide egg shells plus membrane into three groups based on the dry weight. Group A—composed of eggs over 57 grams, have dry shells over five grams; group B—containing eggs weighing 47 to 57 grams, have dry shells over four grams; and group C—those small eggs under 47 grams and have dry shells over three grams. The Jolly numbers of group C may be less than 50 and be fresh, but those in group B will not be fresh when under the 50 mark, and group A when under 63. 5. Normal sized eggs having a Jolly number of only 25 to 45 are probably old eggs. The loss is about one Jolly number (0.1 gram) per day. There is a range of only 0 to 6 grams between stale and fresh eggs,
231
and an accurate instrument is needed to determine this. REFERENCES
Almquist, H. J., and W. F. Hoist, 1931. Variability of Shell Porosity in the Hen's Egg. Hilgardia 6:61. Curtis, M. R., 1911. An Accurate Method for Determining the Weight of the Parts of the Eggs of Birds. Maine Agricultural Experiment Station Bulletin No. 191. Erikson, S. E., R. E. Boyden, J. H. Martin, and W. M. Insko, 1932. The pH of Fresh and Storage Eggs. Kentucky Research Bulletin, No. 335. Givens, J. W., H. J. Almquist, and E. L. R. Stokstad, 1935. Transmission of Light Through Egg Shell. Ind. and Eng. Chemistry 27 :972. Healy, D. J., and A. M. Peter, 1925. American Journal Physical Chem. 74:363. Moran, T., 1937. Gas Storage of Eggs. J. Soc. Chem. Ind. 56:96-101. Olsson, N., 1934. Studies on Specific Gravity of Eggs. Leipzig-Otto Harrassowitz, p. 16. Sharp, P. F., and C. K. Powell, 1931. Increase in pH of the White and Yolk of Hen's Eggs. Ind. and Eng. Chemistry 23:196.
H.
CAER
Department of Agricultural Chemistry, Purdue University Agricultural Experiment Station, Lafayette, Indiana (Received for publication August 15, 1938)
T
HERE has been an unusual interest in the freshness of eggs on the part of consumers in recent years. This awakening may be caused by a wave of food consciousness in general but more probably by the publicity given to possible ways of preserving the freshness for a longer period, such as oiling and use of oil wrappers, carbon dioxide treatments, cold storage temperatures and humidity, water glass solutions, etc.—all of which leads the consumer to ponder over the freshness of breakfast eggs. This study was made to furnish a means of determining the freshness of eggs by showing internal changes in the egg before it is broken. Candling of large supplies of eggs appears to be the best way to grade the carloads which must be handled, but it is too indefinite for the research worker who is concerned with the freshness and flavor of each individual egg. Among the methods noted in the literature for determining the freshness of unbroken eggs are: the variability of shell porosity with age as noted by Almquist and Hoist (1931); the transmission of light through egg shell reported by Givens, Almquist and Stokstad (1935); the movement of ice water through the membranes of fresh but not of stored or stale eggs;1 and the specific gravity of eggs (Curtis, 1911). Progress in determining the condition of the inside of the unbroken egg has been slow and little is known about market eggs until they are broken open. Even then 1
Unpublished data.
there is often much room for doubt as to the quality of the eggs. Time is very important in the taste value of an egg, as each day, with some few exceptions, the yolk gets heavier, the white thinner, and the taste becomes less pleasing. There are many interpretations involved in the term "freshness," but the three which are most evident may be noted as follows: first, the thick white becomes liquid rather rapidly; second, the movement of water from the white into the yolk weakens the membranes around the yolk and makes it tend to flatten out or even break when the egg is opened; and third, the true thick albumen breaks down from loss of water and carbon dioxide. It is the loss of all of these which is small (0.5-0.7 percent per day), but hard to stop, which furnishes a good clue to the age of the egg. Since the proteins which compose the white and yolk of eggs are combined with so much water, especially the white, and since they are partly stabilized when fresh with enough carbon dioxide to make the white rather firm it can be seen that the escape of carbon dioxide from day to day together with the contact with the basic calcium carbonate of the shell will rapidly raise the pH and make a more liquid albumen. EXPERIMENTAL PROCEDURE
It would seem on first thought that the small changes in shrinkage, which eggs undergo daily, are too small to be of importance in evaluating freshness. This loss amounts to only about 0.10 grams per day
[22S]
226
R. H. CARR
per egg and is nearly the same for all eggs regardless of age, from floaters to the best of fresh eggs. Old eggs will float on water while fresh eggs will sink. Approximately a six gram load is required to prevent a fresh egg from sinking. Hence there is a range of only six grams involved, which
grams for the 100 divisions. The dial handle was grooved and attached to the spring coil with a fine wire, thus making it possible to measure small changes with considerable accuracy. The dial reading has been designated as the "Jolly" egg number, after the Munich physicist by that name. The buoyancy weight is obtained by multiplying the dial reading by 0.08 grams. As an example egg No. 50 in Table 1 had a Jolly number of 57 and a buoyancy weight of 4.56 grams (57 x .08 = 4.56).
4 A. Drawing of Jolly egg apparatus.
becomes very important in measuring egg quality and age. An accurate instrument is required to determine each small deviation from the normal fresh or standard egg. The Jolly balance was used to determine this difference in buoyancy. A modified instrument constructed in the laboratory was used (Figure 1). A radio dial was employed to measure the elongation of the spring from which buoyancy weight was calculated. Each division on the dial was found to be equivalent to 0.08 grams or 8
B. Photograph of apparatus as used. EXPERIMENTAL RESULTS
In order to standardize the Jolly balance for eggs it was necessary to find out first what is to be expected in the variations in buoyant effect among day old eggs and to
MEASUREMENT OF FRESHNESS OF UNBROKEN EGGS
find out so far as possible by analysis what causes each of these variations. Fresh eggs were collected from the University Farm and divided in three main groups according to weight. Group A included eggs weighing 57 grams or more, group B eggs weighing 47 to 57 grams and group C eggs weighing less than 47 grams. The weight of the egg, yolk, albumen, and shell and membrane together with the Jolly number and buoyancy weight were determined. The data are given in Table 1. It will be observed from this table that the yolk solid is the heavy portion of the edible part of an egg and usually has more than 50 percent of its weight solid material. It will be noted also that the fresh weights of eggs 45 and 52 indicate heavy yolks, but the small weights of their dried solids show they were watery and were easily detected by their Jolly number and buoyancy weight. The white of an egg consists of three main parts—an outer thin white, a middle layer of jelly white, together with a layer next to the yolk and continuous with the chalazae. It is probably this thick white rather than the total weight of white in an egg that is the most important factor in determining freshness by the Jolly number. The thick white is notable for its high content of the glucoprotein-mucin which is characterized by its ability to swell in water. It was shown by Moran (1937) that at a pH greater than 6 the swelling of mucin particles was so great and their density so near to that of water that it was impossible to separate them in bulk from the solution. He noted also that the decrease in volume and gel strength of the thick white during storage is caused by the chemical breakdown of the mucin and to the shrinkage of the gel framework. When this collapse of the gel has occurred through change in carbon dioxide content, enzyme action, or other reasons the original volume of the thick white is not regained; hence the big shrinkage of this large
227
mass of gel in the thick white, with the production of an airpocket is an outstanding result of storing eggs and this can be detected by the low Jolly number of an old eggThe weight of the shell should make a difference in the Jolly number if it were anything like that of number 58, Table 1, which has a Jolly number of only 31 (buoyancy weight = 2.48 grams) but, of course, this thin crust of a shell and most other shells of this thin chalky structure are easily evident and can be avoided. Egg 45 had a small weight of shell and a very low percentage of dried yolk also; hence a low Jolly number. If it is the amount of albumen that is most desirable in buying eggs for special uses, the small eggs may be very desirable as those noted in Table 1 have relatively three percent more albumen to yolks than the larger egg. In a recent article Olsson (1934) noted that a high correlation was found between the specific gravity and the percentage of shell weight of the total weight of the egg— indicating specific gravity was a good measure of the percentage of shell. The specific gravity of yolk was found to average 1.032, the albumen 1.036, and the shell 2.325. It would appear from Table 1 that shell, yolk, and albumen have to be considered in the Jolly number interpretation. Thus eggs generally may be grouped as A, B, or C on the basis of their dried shell and membrane as follows: Group A—57 gram egg or more, the shell-membrane should weigh over 5 grams; Group B—eggs over 47 grams, shellmembrane should weigh over 4 grams; whereas Group C—eggs under 47 grams weight should average over 3 grams. The data indicate that fresh eggs weighing 57 grams or above will have a Jolly number of 63 or more, those weighing 47 to 57 grams will have a Jolly number of over 50, and those weighing less than 47
228
R. H. CARR TABLE 1.— Data
Egg Egg NumWeight ber
obtained on fresh eggs of different weights
Yolk
Albumen
Fresh Weight
Dry Weight
Gms.
Gms.
Gms.
67 66 47 59 63 70 49 56 45 60 57 65 Average
*68.61 67.85 =64.47 64.31 "63.88 61.95 60.27 "60.16 "59.79 "59.93 58.36 '57.82
19.607 23.551 16.851 20.250 18.942 20.043 19.054 19.829 21.027 18.211 16.588 18.156
Percent Group A 9.880 50 12.551 52 8.821 52 10.367 51 9.699 51 10.998 55 11.311 59 11.989 60 9.445 45 9.429 52 8.611 52 9.110 50
62.28
19.342
10.184
52 54 46 64 53 51 55 50 48 71 Average
"56.51 "56.66 "54.08 "54.43 53.17 51.21 "51.89 50.87 49.72 47.00
22.352 17.077 15.888 15.437 17.443 17.850 16.978 17.807 16.251 18.245
52.55
17.533
61 62 72 73 69 Average
"46.55 "46.87 44.63 "44.07 32.10
24 25 58
Solids
Fresh Weight
Dry Weight
Gms.
Gms.
Shell and Membrane Solids
Fresh Dry SolWeight Weight ids Gms.
Percent
5.956 5.696 5.423 5.463 4.935 5.832 5.819 5.173 3.653 5.057 5.228 6.156
78 70 77 77 69 69 80 76 75 73 73 87
66 67 55 66 63 62 68 74 46 66 63 62
5.28 5.36 4.40 5.28 5.04 4.96 5.44 5.92 3.68 5.28 5.04 4.96
5.366
75
63
5.05
3.915 4.984 4.706 4.907 4.737 4.315 4.271 5.042 4.908 4.660
65 75 79 69 75 63 79 73 72
—
49 61 60 55 59 49 54 57 56 51
3.92 4.88 4.80 4.40 4.72 3.92 4.32 4.56 4.48 4.08
4.644
72
55
4.41
15.197 15.875 11.460 12.215 9.128
57 28.275 3.267 11.3 6.455 Group C (weight, below 47 grams) 7.291 48 25.491 3.032 11.9 5.640 8.506 54 25.071 2.617 10.4 5.676 5.891 55 27.827 3.450 12.4 5.022 54 25.849 3.369 6.638 — 5.882 44 18.076 2.463 13.6 4.769 4.048
3.682 3.822 4.266 4.823 3.753
65 67 85 82 79
47 47 47 53 42
3.76 3.76 3.76 4.24 3.36
42.84
12.771
6.475
4.069
76
47
3.78
"30.53 "17.53 *42.58
0.0 trace 14.581
0.0
46
38 29 31
3.04 2.32 2.48
*—largest egg. B —flat side. °—no yolk—long.
(weight, 41.334 36.234 40.614 36.471 37.471 33.132 33.925 33.515 33.837 34.789 34.155 32.332
PerGms. cent 57 grams or above) 4.776 11.6 7.564 3.692 9.9 8.064 4.224 10.4 7.000 3.471 10.5 6.942 4.895 12.8 7.089 3.652 11.0 8.422 4.071 12.0 7.291 3.754 11.2 6.815 — — 4.829 4.075 11.7 6.686 3.911 11.5 7.178 3.751 11.6 7.092
Jolly BuoyNo. ancy Weight
52 35.651 Group B (weight, 51 28.178 11.263 10.468 61 32.798 8.939 56 31.400 8.167 53 31.645 10.346 59 29.283 8.895 50 26.410 9.976 59 28.661 10.287 58 26.027 9.238 57 26.050 12.032 66 22.294
4.025 11.3 7.081 47 to 57 grams) 3.381 12.0 6.038 3.345 10.2 6.685 3.642 11.6 5.937 4.064 12.8 7.044 3.337 11.4 6.339 2.468 9.5 6.850 3.462 12.0 5.431 2.837 10.9 6.939 2.865 11.0 6.827
—
—
—
9.961
7.477
51
51
24.463 Freak 24.635 14.428 23.163
2.986 Eggs 5.896 2.258 2.883
*—no shell—crust. n —very long—thin.
grams a Jolly number of less than 50. Pullet eggs, eggs without shell and freak eggs will not conform to the above specifications. Table 2 shows the changes that take place in the weight of eggs stored under different conditions. It will be noted that,
12.1
5.398
23.9 15.7 12.5
3.105 3.953
1.831
Gms.
-round—hard to break, -brown egg.
however fresh an egg may have been, it is hard to keep it from losing weight even when it is held in cold storage or wrapped in aluminum foil or oiled. The daily losses in weight given in Table 2 call attention to how regular the loss is and how difficult it is to stop loss in weight and especially how
229
MEASUREMENT OF F R E S H N E S S O F U N B R O K E N EGGS
TABLE 2.—Loss of weight in eggs on storage under different conditions Egg Weight Egg Number
Fresh Gms.
10 Days Later Gms.
25 Days Later
37 Days Later
Gms.
Gms.
Total Loss in Weight
Average Daily Loss in Weight
Gms.
Gms.
Jolly Number Fresh
37 Days Later
Eggs wrapped in aluminum foil—-Stored at 25-27°C. 1 2 3 4
57.899 47.505 62.058 57.609
57.439 47.250 61.688 57.214
57.349 46.682 61.024 56.559
56.416 46.177 60.147 55.882
Average
1.483 1.328 1.911 1.727
0.040 0.036 0.052 0.047
59 49 65 60
40 32 40 39
1.612
0.044
58
38
0.948 1.203 1.187 1.198 1.272
0.026 0.033 0.032 0.032 0.034
57 53 53 59 61
45 38 39 43 46
1.162
0.031
57
42
Fresh
30 Days Later
Eggs in Refrigerator—Stored at 4-5°C. 5 6 7 8 9
55.794 50.563 50.833 56.906 59.495
55.546 50.300 50.479 56.555 59.000
55.283 50.018 50.203 56.268 58.813
Average
54.846 49.360 49.646 55.708 58.223
Eggs Oiled—Machine Oil—Stored at 25-27°C.
10 11 12 13
Fresh
30 Days Later
62.786 54.329 57.400 54.147
62.003 53.870 56.590 53.546
Average
0.783 0.459 0.810 0.601
0.026 0.015 0.027 0.020
63 57 59 56
52 51 48 47
0.663
0.022
59
50
Fresh
14 Days Later
Uncovered and Untreated Eggs—Stored at 25-27°C.
14 15 16 17
Fresh
8 Days Later
14 Days Later
57.240 61.482 53.134 54.337
56.364 60.888 52.106 52.892
55.553 60.353 51.166 51.581
Average
an individual egg is compared to other eggs treated in the same way. It will be noted from Table 2 that although the daily loss in shrinkage may seem small, it is quite constant and hard to stop even in the case of oiled eggs. Thus, because of the regular loss, it is possible by means of the Jolly number to determine the approximate age of eggs, as normal fresh eggs will
1.687 1.129 1.968 2.756
0.121 0.081 0.141 0.197
59 64 55 56
37 49 30 12
1.885
0.135
59
34
have a Jolly number over SO and if below 50 the untreated eggs at room temperature will lose 0.10 gram per day or 0.70 gram per week until they will reach 0 grams (floaters). It was believed that the thickness of the egg white which is so characteristic of fresh eggs had some bearing on the Jolly number. Hence, using wire screen, number 20 mesh,
230
R. H. CARR
wire number 27, tests were made on the fresh eggs studied in Table 1, as well as on other commercial eggs. This consisted of breaking the egg on a screen resting on a beaker, and removing the yolk with the aid of a watch glass or retaining it in the half shell. After the drip had quit the volume of liquid and the thick white on the screen were measured. The data are given in Table 3. It was found that the volume of thick TABLE 3.—Effect
of thickness of albumen on the Jolly number
Egg Thick Thin Num- Albu- Albuber men men
Thick Albumen
Buoyancy Weight
Jolly Number
46 47 48 49 50
cc. 17 22 14 21 12
cc. 12 16 10 10 11
Percent 58.6 57.9 58.3 67.7 52.2
Gms. 4.80 4.40 4.48 5.48 4.56
60 55 56 56 57
51 52 53 54 55 56
23 17 23 23 18 20
1 8 4 7 10 12
95.8 68.0 85.2 76.7 64.3 62.5
3.92" 3.92* 4.80 4.89 4.30 5.82
49 49 • 60 61 53 73
x
Small yolks.
and thin albumen was not important in affecting the Jolly number, as both the stiff and watery white has about the same solid content. It will be noted in Table 3 that the percentage of thick white in fresh eggs varies from 52.1 to 95.8 of total white but this did not materially affect the Jolly number. Sharp and Powell (1931) emphasize the usefulness of pH as a guide to the quality of eggs, noting that the white changes from about pH 7.6 to 9.25 in two days at 37°C, in five days at 16°C, and 10 days at 2°C. This is due to the rapid loss of carbon dioxide in a short time even when eggs are cold. Erikson et al. (1932) stress the value of pH for testing freshness of eggs. Healy and Peter (1925) explain the changes in
the pH of the albumen as due to a disturbance in the bicarbonate buffer system. It has been our observation that all eggs after as little as 48 hours will give a red color when phenolphthalein is added to the shell and membrane. It appears to be reasonable that when the carbon dioxide which is dissolved in the white is released and comes in contact with the calcium carbonate of the shell to form bicarbonates the alkaline reaction produced would hasten the breakdown of the albumen. During the progress of this study, it has been a matter of personal interest to purchase eggs which were represented to be fresh, and later to test them for the Jolly number. It was often found that the eggs were from mixed lots, having in one-half dozen three or four with Jolly numbers over 60, indicating that they were fresh and the remainder having low numbers of 25 to 35, which indicated old eggs. After opening the eggs it was found that the Jolly number indicated the true condition of the egg. Thus by means of the Jolly balance it is possible to determine easily the relative freshness of the unbroken egg. SUMMARY
1. The Jolly balance furnishes a means of checking up on the probable freshness of eggs before they are opened. 2. By using many fresh, day old eggs as a standard it was found that the Jolly number was over 50 for eggs weighing over 47 grams and 63 or more for those over 57 grams. 3. The Jolly number of the normal fresh egg ranging from 50 to 70 grams, regardless of the shape, is dependent on the dry weight of the yolk, which is over half solid, and the shell and membrane, which is about 75 percent solid. The large bag of thick egg white is important in its effect on the Jolly number, as it is largely re-
MEASUREMENT OF FRESHNESS OF UNBROKEN EGGS
sponsible for the air pocket produced when the thick white collapses and loses its gel structure. 4. It is convenient to divide egg shells plus membrane into three groups based on the dry weight. Group A—composed of eggs over 57 grams, have dry shells over five grams; group B—containing eggs weighing 47 to 57 grams, have dry shells over four grams; and group C—those small eggs under 47 grams and have dry shells over three grams. The Jolly numbers of group C may be less than 50 and be fresh, but those in group B will not be fresh when under the 50 mark, and group A when under 63. 5. Normal sized eggs having a Jolly number of only 25 to 45 are probably old eggs. The loss is about one Jolly number (0.1 gram) per day. There is a range of only 0 to 6 grams between stale and fresh eggs,
231
and an accurate instrument is needed to determine this. REFERENCES
Almquist, H. J., and W. F. Hoist, 1931. Variability of Shell Porosity in the Hen's Egg. Hilgardia 6:61. Curtis, M. R., 1911. An Accurate Method for Determining the Weight of the Parts of the Eggs of Birds. Maine Agricultural Experiment Station Bulletin No. 191. Erikson, S. E., R. E. Boyden, J. H. Martin, and W. M. Insko, 1932. The pH of Fresh and Storage Eggs. Kentucky Research Bulletin, No. 335. Givens, J. W., H. J. Almquist, and E. L. R. Stokstad, 1935. Transmission of Light Through Egg Shell. Ind. and Eng. Chemistry 27 :972. Healy, D. J., and A. M. Peter, 1925. American Journal Physical Chem. 74:363. Moran, T., 1937. Gas Storage of Eggs. J. Soc. Chem. Ind. 56:96-101. Olsson, N., 1934. Studies on Specific Gravity of Eggs. Leipzig-Otto Harrassowitz, p. 16. Sharp, P. F., and C. K. Powell, 1931. Increase in pH of the White and Yolk of Hen's Eggs. Ind. and Eng. Chemistry 23:196.