32 MISC. PUBLICATION 168, U. S. DEPT. OF AGRICULTURE 



SYMPTOMS OF FREEZING INJURY 



External Appearance 



If freezing has been slight, there may be no marked external 

 symptoms of any sort; if it has been severe, the general outside 

 appearance of the apple is strikingly affected. The surface be- 

 comes discolored in irregular-shaped areas very soon after the 

 apple thaws and appears considerably darkened. It often assumes 

 a water-soaked appearance and a brown color closely resembling 

 the color of apple scald. It may become much darker, in some 

 cases almost black. When apples are in a frozen condition the 

 skin becomes temporarily shriveled, the shriveling usually occur- 

 ring in the form of a network of wrinkles rather than as parallel 

 lines of shrinkage such as are produced by normal evaporation. 

 Careful measurements have shown that the fruit actually becomes 

 smaller, sometimes by as much as 10 percent of its original 

 volume. The reduction in size is shown also by the fact that if 

 the apples in a packed box or basket become frozen they rattle 

 around when the container is shaken, even though the pack was 

 tight before freezing occurred. On thawing, the pack regains 

 practically its original volume, unless the freezing was very severe. 



When an apple thaws after having been badly frozen the skin 

 becomes shriveled, particularly if the air in the storage place is 

 very dry. This form of shriveling seems to be due to rapid 

 evaporation of the water withdrawn from the cells and changed 

 into ice in the spaces between the cells during the freezing process. 

 Shriveling, when slight, is accompanied by a reduction chiefly in 

 size ; when severe, by a marked reduction in both size and weight. 



Apples that have been severely frozen frequently show notice- 

 ably sunken spots, which may be % inch deep or more and have a 

 superficial diameter about equal to their depth. In virtually all 

 cases these sunken spots develop at places that were bruised while 

 the apple was still frozen. (See Bruises, p. 21.) 



Apples that have been both bruised and frozen while in transit 

 by rail frequently show flattened areas, 1% to 2 inches in diam- 

 eter, that are somewhat sunken and soft toward the center and 

 have a dull-brown or slate color over most or all of the surface. 

 Transit bruises, described on page 21, are smaller in diameter, 

 and flat instead of sunken, the skin covering them is not slate- 

 colored, and the flesh beneath is firm. 



It should be remembered, however, that during a short exposure 

 to an air temperature several degrees below freezing considerable 

 ice may form within the tissues and yet produce little or no effect 

 that could be diagnosed as freezing injury. 



Internal Appearance 



Usually the best indications of freezing injury are found by 

 examining a cross section of the fruit. If a cut is made crosswise 

 through the middle of an apple that has not been frozen, there 

 will be seen, about halfway between the center and the outside, 

 10 small dots, the natural color of which in most varieties is green 

 or yellowish green, but of which in Winesap, Esopus Spitzenburg, 

 and some other varieties is occasionally tinged with red. These 

 dots are the cut ends of the main fibrovascular bundles of the 

 apple, which are connected with numerous but less conspicuous 



