-1- 



S70RAC-5 l.IAITAGEIiEl^T 



Good cold storage management goes beyond the maintenance of suitable tempera- 

 tures alone. One of the frequently neglected operations in commercial storages is 

 the maintenance of a high relative humidity. 



Apples are about 85/o water and the intercellular spaces v/ithin the fruit may 

 be assumed to be saturated vrith v;ater vapor at any given temperature. Consequently, 

 apples v/ill lose moisture whenever the surrounding atmosphere has a relative 

 humidity below 100$'=, At any given temperature, the lower the relative humidity 

 the faster the rate of moisture loss by the fruit, 



V»l-ien apples lose about 5/j of their weight as v/ater vapor, visible shriveling 

 is apt to occur. It would seem that the simplest thing to do to reduce losses 

 v>rould be to maintain a relative humidity of 100/b, However, it is difficult to do 

 so at 32° F, Even if it were possible, it is undesirable since a saturated atmos- 

 phere is ideal for mold and fungus grovrth on boxes, walls, and fruit, A musty 

 odor may develop and be absorbed by the fruit and readily tasted by the consumer* 

 A relative huiaidity of 85 to 90/J is considered most desirable. 



Chief Factors VHiich Tend to Loiver the 3Iumidit y. (l) Dry Poxes , It has been shovm 

 that a b'o'nW-dry field crate nay absorb up to one pound of v/ator in a cold storage, 

 TJhen there are 10,000 dry boxes in a room they may absorb enough v/ater to be 

 equivalent in weight to 250 bushels of apples. Unless water is added to the room 

 the moisture absorbed by the boxes will come largely from the apples, IVe have had 

 a dry harvesting season. Many boxes were very dry v.-^hen they went into storage. 

 Don't hesitate to soak then dovm ivith a hose even after they are in storage, 

 (2) Cold Coils . The lower the tomperature of the refrigerant in the coils the 

 greater the amount of water vapor v;hich v;ill condense on then as frost. V.lien the 

 fruit has been cooled to the desired point and outdoor temperatures are cooler, 

 raise the refrigerant temperature if possible, 



Maintenanco of Suitable Relative Kuniditios . Vmen the relative humidity is belov/ 

 65>i there are several v/ays in which it can bo raised. Some operators atomize water 

 into the air by the use of commorcial humidifiers or home made outfits. Vnien one 

 considers tlic quantities of vrater ivhich can be absorbed by dry boxes it is obvious 

 that those units must deliver large qiiantitics of v/ater vapor to be effective. 



The boxes and floors may be v;ct dorm periodically v;ith a hose. If one adds 

 no vrater to the room until it is fillod to capacity this method is probably not 

 nearly as effective as it v;ould be if it is done each day as the fruit is moving 

 into the room because one just can't get the v/ater quickly to all parts of the 

 room once it is full. 



How t_o j-ioasurc Relative Hujnidity . The instruments availably for measuring relative 

 humidity are numerous. Frequently those tj'pos vmich can be read directly, such as 

 hair hygrometers, arc popular because thoy can be road as easily as a thermometer. 

 However, they are not consistently as accurate as a s ling psychrometor \^hich r/e 

 recommend for this purpose. If any substitute is used it should be checked fre- 

 quently v/ith a sling psychrometor. A sling psychrometor consists of two thermom- 

 eters fastened to a v/ooden or metal backing so that they may be twirled on a handle. 

 The bulb of one thermometer is enclosed in a cloth wick v.'hich is moistened (v:et 

 bulb) v/hilc the other remains uncovered and dry (dry bulb). As the thermometers 

 are twirled (air movonent ovor the wet bulb is necessary) v;ater evaporates from 

 t!ic v;st bulb tuid since evaporation is a cooling process the temperature of the vxet 

 bulb is reduced as compared to the dry bulb except when the relative humidity is 



ioo;a. 



