STORAGE OF FRUITS, VEGETABLES, AND FLORISTS' STOCKS 5 



perature between the refrigerant and the air of the room, thus rais- 

 ing the dew point of the air and its relative humidity. This permits 

 the maintaining of high humidity. For low humidity the tempera- 

 ture of the refrigerant is lowered. To build up humidity quickly 

 in cold-storage rooms some operators evaporate water from insulated 

 open-top tanks equipped with insert electrical heaters. Others use 

 a fan to beat water into very fine particles, and to blow this spray 

 into the room. These humidifiers are sometimes made automatic, 

 connecting with humidistats. However, if the coil temperature is 

 too low, that is, if the spread between the temperature of the refrig- 

 erant and that of the room is too great, the effect of these various 

 measures will be short-lived. The relative humidity will soon become 

 undesirably low, and harmful drying out of the stored product will 

 occur. 



When warm products are placed in a cold room the spread between 

 commodity temperature and refrigeration temperature is wide at 

 first. Such a condition hastens cooling and shortens the time during 

 which undesirable changes can occur in the commodity. As the 

 spread is reduced, the cooling proceeds more and more slowly. 

 Eventually, if the temperature of the refrigerant is properly adjusted 

 and there is adequate refrigerated surface, the desired temperature 

 can be reached without subjecting the commodity to excessive desic- 

 cation. If it could be successfully managed under commercial con- 

 ditions, a temporary reduction in refrigerant temperature below what 

 is desired or safe for long-time operation would be extremely helpful 

 in shortening the initial cooling period. 



Operators of certain large cold-storage houses have found that 

 when a room is filled with apples or celery, for example, the relative 

 humidity soon becomes constant at a fairly definite level, which for- 

 tunately is about the optimum for the particular commodity con- 

 cerned. The same result has been observed with other commercially 

 important fruits and vegetables and probably is obtained in many 

 of the larger, well-constructed cold-storage warehouses of the country. 

 This is probably due to the fact that when a storage room is nearly 

 full and there is comparatively little air space left the pull on the 

 moisture in the produce is less, and it is easier to maintain the desired 

 humidity. In these cases, however, it must be assumed that the spread 

 between coil temperature and air temperature is kept narrow. 



For most fruits that are stored commercially the statement is true 

 that a relative humidity of 80 to 90 percent gives the best results. 

 Exceptions are discussed at various places in the text. For leafy 

 vegetables and root crops the relative humidity should be about 90 

 to 95 percent; for other vegetables, except as noted in the text, 85 to 

 90 percent. If it seems necessary to increase the relative humidity 

 in rooms used for common or air-cooled storage, this can best be done 

 b} r sprinkling the floor occasionally. Earth floors are more desirable 

 in air-cooled storages than floors of concrete because they are more 

 easily kept damp. An increase in air circulation calls for an increase 

 in relative humidity, if wilting of the stored commodity is to be 

 avoided. Allen and Pentzer (#) found that doubling the rate of air 

 movement increased moisture loss by about one-third and was equiva- 

 lent to about a 5 -percent drop in relative humidity. The drying effect 

 of increased rate of air movement is particularly marked if the hu- 

 midity of the air is lower than the moisture content of the commodity. 



