Storage Humidity Influences Quality 

 of Mcintosh Apples 



William J. Bramlage 



Department of Plant & Soil Sciences, University of Massachusetts 



Very few apple storage operators in the North- 

 east give any consideration to humidity levels in the 

 storage. In part, this is because it is difficult to 

 measure humidity accurately when it is near 100%. 

 I do not know of any New England storage, except at 

 the University of Massachusetts Horticultural Re- 

 search Center in Belchertown, that is equipped to 

 measure storage humidity. Yet, humidity is an 

 important variable in determining the quality of 

 fruit after storage. 



We are reminded of this by a recent report of 

 research by Dr. Perry Lidster, conducted at the 

 Agriculture Canada Research Station in Kentville, 

 Nova Scotia (J. Amer. Soc. Hort. Sci. 115:94-96, 

 1990). In this study, Mcintosh apples were stored in 

 either standard CA (3% 2 , 5% C0 2 , 37T), or in low- 

 oxygen CA (1% 2 , 0.5% C0 2 , 37T). In each atmos- 

 phere, relative humidity was maintained at 75%, 

 81%, 89%, 92-96%, or 96-100%. The total experi- 

 ment was repeated in two separate years. 



Humidity influenced fruit quality after storage 

 in a number of ways. As you would expect, weight 

 loss increased as relative humidity fell, due to evapo- 

 ration of water from the fruit. For example, in 

 standard CA one year, fruit lost 4.4%, 2.7%, 2.5%, 

 1.0%, and 0.3% of their original weight during stor- 

 age at 75%, 81%, 

 89%, 92-96%, and 

 96-100% relative 

 humidity, respec- 

 tively. In addi- 

 tion, fruit lost 

 more firmness 

 during storage as 

 humidity was 

 reduced, and 

 these differences 

 were still meas- 

 urable after 7 

 days at room tem- 

 perature. Fruit 

 also were pro- 

 gressively less 

 permeable to 



gases as humidity was reduced; low permeability 

 can interfere with normal respiration by fruit at CA 

 conditions. 



The clearest effects of humidity during storage 

 were on the development of various disorders in the 

 fruit after storage (Table 1). It commonly is recom- 

 mended that apple storages be operated at 90-95% 

 relative humidity. Humidities lower than this did 

 not increase the occurrence of disorders in standard 

 CA, and in fact 75% lowered the amount of senescent 

 breakdown that occurred. (Similar results have 

 been reported before.) However, humidity at greater 

 than 95% increased senile brown core and senescent 

 breakdown. The effect on rotting was not statisti- 

 cally significant, but there tended to be more rot with 

 very high humidity. These results are consistent 

 with those in earlier studies, indicating that very 

 high humidity encourages senescent disorders in 

 apples. 



However, in low oxygen storage, effects of 

 humidity on disorders were quite different from 

 those in standard CA (Table 1). Low humidities 

 clearly increased epidermal bluing and cortical 

 browning, both of which are symptoms of oxygen 

 deficiency. It is likely, therefore, that low humidity 

 caused greater occurrence of these disorders by 



Fruit Notes, Winter, 1991 



