MASS. EXPERIMENT STATION BULLETIN 360 



Humidity 



Repeated experiments have shown that under cold-storage conditions a relative 

 humidity of 85 percent is adequate to prevent shriveling. Roxbury Russet and 

 Golden Delicious tend to shrivelmore readilythan varieties suchas Mcintosh and 

 Baldwin, because of the absence of a waxy coating over the skin which, when 

 present, retards the loss of moisture. Therefore, the maintenance of a relatively 

 high humidity is of special importance where varieties of the former type are to be 

 stored. An excessively high humidity not only is difficult to maintain but may be 

 objectionable in that it provides favorable conditions for the development of 

 rots and molds. 



There may be some difficult} in maintaining a huniiditx 

 of 85 percent in a refrigerated storage during the loading 

 period. Continuous operation of the compressor will cause 

 heavy frosting of the coils, and this removal of moisture from 

 the air may reduce the relative humidit>- to as low as 70 per- 

 cent. Usually there is no difficulty in bringing up the humid- 

 ity when the initial cooling of the fruit is completed. 



The most satisfactory method for determining humidity is 

 by means of a sling psychrometer. Hair h>grometers are more 

 convenient to read but are less accurate and require fre- 

 quent checking. 



During the season of 1935-36 an experiment was conducted 

 to determine what effect this low humidit\ might have on the 

 subsequent condition of the fruit. Three lots of Mcintosh 

 apples were stored at 32° but at different humidities from 

 September 27 to November 2^. after which they were all 

 stored at 85 percent relati\e huniidit\'. The conditions under 

 which the various lots were stored and the loss in weight of 

 each are shown in Table 1, and the losses are shown graph- 

 ically in Figure 4. 



Table 1. 



Loss OF Weight of McIntosh Apples Stored 

 UNDER Different Conditions. 



Figure i. 

 SlinR P.-ychrometer. 



This experiment was repeated the following year with comparable results. 

 The data and observations from these two experiments indicate that, while there 

 may be a slight loss of moisture from apples at low humidilx', it will not cause 

 shriveling or any appreciable iiijurN to the fruit if it continues oiil\- while the 

 storage is being filled. 



Apples tend to lo.se moisture more readih- in common storage because evapora- 

 tion is more rapid at the higher temperatures. Therefore, a relative humidity 

 of not less than 85 percent should he constantly maintained in a common storage. 



