MARKET DISEASES OP FRUITS AND VEGETABLES SI 



outer parts of a load, there should be no transit freezing elsewhere 

 in the car. If the injury is uniformly scattered through the 

 packages and through the load, in all probability freezing took 

 place before the product was loaded. 



The amount of injury that an apple may suffer from freezing 

 depends on the length of the exposure to low temperature, on how 

 low the temperature goes, and on other conditions affecting the 

 fruit when freezing occurs. Usually these conditions, as well as 

 the rate of thawing, are unknown when apples are inspected and 

 conclusions must be drawn from the appearance of the fruit at 

 that time. 



When apples freeze, ice crystals form within the tissues, not 

 in the cells but between them. The quantity of ice which forms 

 depends on the duration of cold and the minimum temperature 

 which the tissues reach. As the tissue temperatures fall, more and 

 more water is withdrawn from the cells and greater quantities of 

 ice form. Formation of a small amount of ice in the tissues causes 

 little damage if the fruit is not handled while frozen, as would be 

 the case while the fruit is on the tree. If the temperature of the 

 tissues becomes sufficiently low to build up large quantities of ice, 

 however, serious injury or death of tissues results. 



The presence of ice in an apple at the time of examination is 

 not evidence that serious freezing injury has occurred. Doubt- 

 less any ice formation injures the apple flesh to some degree, but 

 there is no visible evidence of injury from slight freezing and 

 no effect upon the market value of the fruit. If the freezing 

 process proceeds somewhat further, however, a slight noticeable 

 injury results, even though the cells may appear practically 

 normal; if it proceeds still further, the cells may be killed and 

 turn brown. Unless a significant proportion of the cells show 

 this browning it is inaccurate to say that an apple shows freezing 

 injury. 



FREEZING POINT OF APPLES 



Accurate determinations on several hundred specimens of the 

 more important commercial varieties of apple (Winesap, Stay- 

 man, Yellow Newtown, Ben Davis, Baldwin, Rome Beauty, 

 Wagener, Jonathan, Mcintosh, Tompkins King, and Grimes Gold- 

 en) showed that the freezing point ranges from 27.3° to 29.4° F. ; 

 the average is 28.4°. Unless the temperature of the air sur- 

 rounding an individual specimen is suddenly lowered much be- 

 low 27° to 29°, the temperature of the inside tissues often 

 drops temporarily a degree or more below the true freezing 

 point without any formation of ice. This phenomenon — lower- 

 ing the temperature of the tissue below its freezing point 

 without inducing the formation of ice crystals- — is known as 

 undercooling. If the temperature continues to fall or if the 

 exposure to the low temperature is prolonged, the resistance to 

 freezing is overcome, the undercooling period ends, ice quickly 

 forms in the tissues, and the temperature rises rapidly to the 

 approximate true freezing point regardless of the air temperature 

 around the apples. After ice forms in the tissues a further drop 

 in the temperature of the surrounding air will be reflected in the 

 temperature of the fruit. 



