Aug. 1, 1924 
Freezing Injury of Apples 
107 
amount of ice formation is required 
before injury results. Freezing points 
of a large number of apples of a certain 
variety were determined. When this 
was accomplished the apples were 
allowed to remain in the freezing room 
and further records were made of 
their internal temperatures. 
Table VII.— Effect of different thaw¬ 
ing temperatures on the depth of 
bruises made with SO pounds pressure 
on hard frozen Esopus Spitzenburg 
apples 
Condition when 
bruised 
Thaw¬ 
ing 
tem¬ 
pera¬ 
tures 
Dura¬ 
tion of 
expo¬ 
sure to 
thaw¬ 
ing 
tem¬ 
pera¬ 
tures 
Bruise 
depth 
Unfrozen.. 
° F. 
70 
Hours 
24 
Mm. 
5.1 
Frozen.. 
70 
24 
15.3 
Do.. 
70 
48 
15.0 
Unfrozen_ _ 
70 
72 
5.0 
Frozen. 
70 
72 
16.8 
Unfrozen__ 
50 
24 
5.1 
Frozen..__ 
50 
24 
15.4 
Do.. 
50 
48 
14. 0 
Unfrozen... 
50 
72 
6.0 
Frozen_ 
50 
72 
16.2 
Unfrozen... 
40 
24 
5. 5 
Frozen.. 
40 
24 
15.0 
Do.. 
40 
48 
19.3 
Unfrozen_ 
40 
72 
5.1 
Frozen. 
40 
72 
14.9 
Unfrozen_ _ 
32 
24 
5.1 
Frozen. 
32 
24 
14.3 
Do. 
32 
48 
13.4 
Unfrozen.. 
32 
72 
5.1 
Frozen.. 
32 
72 
14.8 
Ratio 
of 
depth 
of 
frozen 
to un¬ 
frozen 
bruises 
3.0 
3.4 
3.6 
2.7 
2.7 
2.9 
2 ." 8 
2.9 
The internal temperature in an apple 
exposed to freezing conditions usually 
drops below the freezing point, that is, 
it is undercooled. If the temperature 
is reduced enough, ice crystals begin 
to form, and the heat of fusion pro¬ 
duced in the formation of the ice 
crystals raises the temperature of the 
apple to a point where it remains prac¬ 
tically stationary, or with only slight 
reduction, until part of the water in 
the tissues which can be frozen out 
in the form of crystals of ice has been 
thus changed. The point at which the 
temperature remains constant is called 
the freezing point. After this is 
reached the temperature of the apple 
gradually becomes lower and ap¬ 
proaches that of the room or environ¬ 
ment of the fruit, where it can be held 
almost indefinitely after some minor 
fluctuations. 
IfckThese fluctuations may be due to 
the further crystallization of small 
amounts of water which are forced 
from the liquid state by the increasing in- 
99180—251*-2 
ternal tension in the cells of the apple as 
the temperature continues to fall. Fig¬ 
ure 1 shows a typical curve of the freez¬ 
ing of a Yellow Newtown apple, and il¬ 
lustrates the points mentioned above. 
A portion of the curve showing the 
temperature drop while the fruit was 
being cooled from the storage temper¬ 
ature of 34° F. has been omitted for 
the sake of brevity. The reactions of 
the fruit noted during and after the 
freezing process suggest that visual 
injury occurs when the temperature 
drops a certain distance below the 
freezing point. This injury is prob¬ 
ably due to the loss of water from the 
protoplasm of the cells, which has been 
shown to occur during the freezing 
process. In other words, the internal 
temperatures measured as freezing goes 
on are an indirect measure of the 
amount of ice which has been formed; 
and this degree of ice formation may 
determine the occurrence of visual 
injury for any set of internal con¬ 
ditions in the fruit. It will be shown 
elsewhere that other changes also 
seem to occur in the fruit as soon as 
ice formation has taken place. 
To obtain further information on 
the internal temperatures of frozen 
apples at which visual injury occurs, 
readings of the freezing point and of the 
internal temperatures when the fruit 
was removed from the freezing room 
have been collected, together with other 
relevant data. These are so volumi¬ 
nous that they are presented only in 
brief summary form to bring out certain 
facts (Table VIII). 
The temperatures prevailing in the 
freezing room while the different lots 
were under observation did not vary 
widely for the three varieties. The 
maxima and minima were 22.3° F. and 
21° for the Ben Davis, 22.7° and 21.9° 
for the Winesap, and 22.4° and 21.3° 
for the Rome Beauty. All the apples 
in this experiment were grown on Ar¬ 
lington Experiment Farm, Rosslyn, Va. 
In the case of the frozen Ben Davis 
apples studied, Table VIII indicates in 
the average only a small amount of 
visual injury when the internal tem¬ 
peratures were 4° F. below the freezing 
point. Below this point the percentage 
of injury increased rather sharply, 
though not markedly, so that in the 
group where the temperature was 6.1° 
to 7° below the freezing point nearly 
two-thirds of the apples showed visual 
injury. No injury appeared in 14 
apples of this variety when the internal 
temperatures dropped from 3.1° to 4° 
below their freezing points. 
The internal temperature of frozen 
Winesap apples could not go so far 
below their freezing point without 
