14 CIRCULAR 659, U. S. DEPARTMENT OF AGRICULTURE 



removed from the fruit; therefore, it is especially important to maintain 

 an optimum relative humidity in cold storages with air-circulating sys- 

 tems, especially when fruit is stored in orchard crates or boxes. Observa- 

 tions in commercial cold-storage plants have shown that the relative 

 humidity in the apple-storage rooms is frequently less than 85 percent, 

 sometimes as low as 70 percent. 



To maintain desirable humidity conditions so as to reduce wilting, 

 it is well to fill the storage rooms, thus reducing as much as possible the 

 ratio of air to fruit. 



In designing a cold-storage plant it must be remembered that most of 

 the moisture producing frost on the coils or diluting the brine used in a 

 brine-spray chamber daring the storage period comes from the fruit. 

 The greater the temperature difference between the air and the cooling 

 medium, whether it be coil surface or brine spray, the more rapid the 

 condensation of moisture and the greater the drying effect on the at- 

 mosphere, thus increasing the pull on the fruit and causing wilting. 

 Use of a brine spray in an air-circulating system is no insurance against 

 low relative humidity; it will have the reverse effect if the temperature 

 of the brine is greatly below that of the air. Consequently, it is essential 

 that there be enough coil capacity, or enough coil capacity plus volume 

 of brine spray, to provide the desired refrigeration without the cooling 

 medium being more than 7° or 8° F. below the air temperature of the 

 room (11). The adequacy of the building's insulation may play an im- 

 portant part in preventing shrivel in fruit, because the better the insula- 

 tion the less difference there will be between the temperature of the air 

 and that of the cooling medium. 



It is difficult to raise the humidity in a cold-storage room kept within 

 the most desirable temperature range for apples, 30° to 32° F., because 

 the moisture is so quickly condensed and frozen. However, if it be- 

 comes necessary to raise the humidity, it can be done best by using a 

 humidifying apparatus that introduces steam into the air of the storage 

 room. A simple humidifier of this type can be made by placing a shallow 

 pan of water on some strip heaters, operation of which is controlled 

 through a humidistat. An electric fan should be arranged to blow over 

 the surface of the water. The efficiency of the apparatus can be in- 

 creased somewhat if absorbent toweling is looped into the water from a 

 series of parallel supports placed 8 to 10 inches above the surface of the 

 water. In this arrangement the air current from the fan should pass 

 through the loops of the wicking. Adding moisture to raise the humidity 

 by any method is only an expedient, not the most satisfactory method 

 of controlling wilting and shrinkage. All that can be accomplished by 

 evaporating moisture into the storage air is to meet some of the moisture 

 requirement of the air rather than to permit it all to be taken from the 

 apples. The moisture requirement of the air cannot be satisfied so long 

 as the temperature of the cooling surfaces remains markedly below that 

 of the air. 



Other measures used to some extent to avoid the wilting effects of 

 dry atmospheres are the coating of apples with wax or packing them in 

 packages having moistureproof liners. These expedients have to be used 

 with a degree of caution, as there is danger of sealing the apples too well, 

 in which case the oxygen within the fruit is reduced to a point where the 

 fruit cannot respire normally; this results in development of undesirable 



