lowering gas permeability of the 

 fruit. Furthermore, the very 

 high humidity did not have an 

 adverse effect in low oxygen CA, 

 as it did in standard CA. 



These results indicate that 

 the effects of humidity follow 

 several patterns. In terms of 

 fruit condition, humidity should 

 be kept as high as possible. 

 However, in terms of occurrence 

 of disorders, humidities above 

 95% are detrimental if senescent 

 disorders are a concern, as they 

 are in air storage or standard 

 CA. But if the storage is being 

 run as a low oxygen CA, the 

 threat is not senescent disorders 

 but ones due to disruption of 

 respiration, and here, humidity 

 as high as possible would be 

 beneficial. 



In New England we have 

 had no success with low oxygen 

 CA and have never recom- 

 mended its use. Thus, humidity above 95% is not 

 desirable in our apple storages. We should be trying 

 to maintain about 92-95% relative humidity. Lower 

 levels cause loss of fruit condition and high levels 

 enhance senescent disorders. 



What can a storage operator do to maintain 

 appropriate relative humidity? It cannot be con- 

 trolled because it is not even being measured! Yet, 

 basic procedures will provide reasonable assurance 

 that relative humidity is probably between 90 and 

 95%. Making sure that rooms and bins have ab- 

 sorbed ample water before loading avoids the prob- 

 lem of dry wood absorbing large quantities of water 

 from the air during storage. Placing water on the 

 floor provides an evaporating surface other than the 

 fruit. However, correct operation of the cooling 

 system is the most fundamental way to avoid inap- 

 propriate storage humidity, because the cooling coils 

 have a drying effect on the storage atmosphere by 

 causing ice to form on the coils (thereby taking water 

 from the air). 



Table 2. Minimum relative humidity levels (%) developed at 

 various storage and evaporator discharge temperatures. 

 (From: Bartsch, J. A and G. D. Blanpied. 1984. Refrigeration 

 and Controlled Atmosphere Storage for Horticultural Crops. 

 NRAES-22, Cooperative Extension, Cornell University, Ithaca, 

 NY 14853.) 



*Actual airstream temperature drop between inlet and outlet. 

 The coil temperature difference will be approximately twice 

 this value. 



The minimum humidity level in the storage 

 atmosphere is determined primarily by the tempera- 

 ture difference ("split") between the evaporator inlet 

 and outlet. The effect of this "split" on relative 

 humidity in the room is shown in Table 2. The "split" 

 must be no more than 2* or 3* or humidity will be too 

 low. On the other hand, if it is 1* or less, humidity 

 may become high enough to enhance the occurrence 

 of senescent disorders. 



It is often believed that "wet" coils (using a brine 

 spray defrost) produce higher humidity than do 

 "dry" coils. This is not true. In fact, "wet" coils often 

 produce lower humidities than "dry" coils, especially 

 at lower temperatures. What is important is not 

 whether coils are "wet" or "dry", but rather, the 

 temperature drop across the evaporator. 



The effects of humidity in storage on apple 

 quality are often forgotten in the worries over tem- 

 perature and atmosphere, but as Lidster's data 

 clearly show, the humidity in the storage may have 

 much to do with the quality of the fruit when it is 

 taken from the storage. 



Fruit Notes, Winter, 1991 



