126 
Journal of Agriculutral Research 
Vol. XXIX, No. 3 
2. Cooling apples below their freezing 
points without the formation of ice in 
the tissue does not cause any visual in¬ 
jury or perceptible softening of the fruit. 
3. Undercooling of isolated apples 
can sometimes be carried to a point as 
low as 7 or 8 degrees below their freez¬ 
ing point without ice formation, pro¬ 
vided the fruit is left undisturbed. 
4. Inoculation or the beginning of 
ice formation in apples takes place 
rather slowly at times, and ice forma¬ 
tion in the tissues does not spread so 
rapidly as in some other plant organ¬ 
isms that have been studied. 
5. The bruising of apples while they 
are hard frozen results in a much more 
serious injury than does a similar pres¬ 
sure on unfrozen fruit. Consequently, 
any handling of frozen apples will usu¬ 
ally result in more or less severe bruis¬ 
ing injury. 
6. The severity of the injury caused 
by bruising frozen apples is lessened as 
the amount of ice in the tissues de¬ 
creases during thawing. 
7. Bruises made on apples before 
they are frozen do not become more 
serious as to depth when the fruit is 
frozen, nor do they change materially 
in appearance. 
8. There are no significant differences 
in the depth of bruises on hard-frozen 
fruit when subjected to different thaw¬ 
ing temperatures. 
9. Visual freezing injury may be 
classed under two heads, that appear¬ 
ing in the tissues of the apple, and that 
appearing on the surface, both being 
found in the same apple or occurring 
independently. 
10. Visual freezing injury exhibits 
a great variety of forms and intensities 
which depend not only on the severity 
and duration of the prevailing freezing 
temperatures, but also on other factors, 
such as the physiological condition of 
the fruit. 
11. The point to which the internal 
temperature of an apple must be 
reduced before visual injury occurs 
varies widely with the time of exposure 
to the temperature, with the variety, 
and with the individual apple. Under 
conditions of moderate thawing rates 
and rather short exposures to freezing 
conditions, it was found that the in¬ 
teriors of the apples usually had to 
reach a point at least 2° to 3° below 
the actual freezing temperatures after 
ice formation had started, before visual 
injury occurred. As the internal tem¬ 
perature dropped lower there was a 
rapid increase in the amount and 
severity of the injury, due probably to 
the increase in the quantity of ice 
formed in the fruit. 
12. The data on the rate of cooling 
down of different packages at different 
freezing temperatures emphasize that 
apples can be exposed in such packages 
for considerable periods of time with¬ 
out the occurrence of any considerable 
actual freezing. There is some evidence 
that apples scattered through different 
parts of the package do freeze and that 
the heat produced by the ice crystalli¬ 
zation in their tissues raises the temper¬ 
ature of the mass of fruit as a whole 
sufficiently to delay freezing in it. It 
does not seem possible to carry the un¬ 
dercooling of apples in packages to the 
degree to which it has been shown to 
occur in isolated, undisturbed apples, 
surrounded on all sides by cold air. 
13. The fruit in the lower part of 
a package held under freezing condi¬ 
tions is exposed to a greater danger of 
freezing injury than that in any other 
portion of the package. 
14. Wrapping serves to hinder the 
loss of heat from fruit under freezing 
conditions, thereby delaying the forma¬ 
tion of ice in the fruit tissues. In this 
way the amount and severity of the 
freezing injury may be reduced, as re¬ 
gards both that determined visually and 
by means of other tests. 
15. Repeated freezing and thawing 
of apples causes a progressive increase 
in the freezing injury, though not so 
great an increase as a prolonged con¬ 
tinuous exposure. Thus two exposures 
of 90 hours each to freezing conditions 
will cause more injury than one ex¬ 
posure of 90 hours, but less than one 
exposure of 180 hours. 
16. There is no evidence of progres¬ 
sive and sustained raising of the freez¬ 
ing point of apples held in 32° F. 
during the storage season. The greater 
susceptibility of apples to freezing 
injury as the storage season progresses 
lies apparently in a change in the 
physiological condition of the fruit and 
is not determined by a changing freez¬ 
ing point. 
17. The temperatures at which apples 
are ordinarily thawed have only 
a slight effect upon the subsequent 
condition of the fruit. Yet very high 
temperatures and low humidities are 
not recommended because of the rapid 
water loss from the fruit under such 
conditions and the more rapid develop¬ 
ment of other injurious effects. 
18. There is a distinct weakening in 
the keeping quality of apples when they 
are frozen, even when there is no visual 
evidence that freezing has occurred. 
The tissues of frozen apples are softer 
and more mealy after thawing and 
in poorer condition to stand storage 
and marketing, even though no direct 
discoloration has occurred. The degree 
of this softening again varies with the 
exposure and intensity of the freezing 
period. 
