4 CIRCULAR 2 7 8, U. S. DEPARTMENT OF AGRICULTURE 



the spread between the temperature of the refrigerant and that of 

 the room is more important in maintaining humidity than in pre- 

 venting fluctuations in the room temperature. This point is dis- 

 cussed in more detail on page 5. Storage rooms should be equipped 

 either with reliable, accurate thermostats or with means for manual 

 control which are given frequent personal attention by someone 

 charged with that duty. Even when reliable automatic controls are 

 used, they should be checked periodically by some responsible 

 person. 



In commercial cold-storage rooms thermometers are usually placed 

 at a height of about 5 feet, sometimes slightly lower, for conven- 

 ience in reading. It is important, however, to take temperatures 

 frequently at the floor and the ceiling also, and at any other places 

 where they might be expected to be undesirably high or low. In 

 providing recommended temperatures for given products, considera- 

 tion should be given to differences between the temperatures of the 

 air at the position of the thermometer and at different places around 

 the packages of the stored product, and also to differences between 

 air and commodity temperatures. Often the packages are piled too 

 closely together or distribution of refrigeration is inadequate to reach 

 all parts of the piles of the stored commodity, and it is not unusual 

 under such conditions to have commodities remain for several days 

 or even weeks at temperatures several degrees higher than those in- 

 dicated by the thermometer. This condition can be detected by open- 

 ing the pile and taking commodity temperatures and can be cor- 

 rected by wider spacing of packages and the use of portable fans 

 and baffles for the direction of air currents to the centers of the 

 piles. The installation of such equipment will also be useful in pre- 

 venting dead-air pockets that are hard to cool, especially in rooms 

 cooled by direct-expansion coils or by brine coils and without means 

 for air circulation. 



The importance of maintaining fairly constant temperatures in 

 cold-storage rooms lies in the effect of such control, or the lack of it, 

 on the keeping quality of stored commodities. Most varieties of 

 apples keep best and longest if held constantly at 30° to 32° F. ; the 

 best temperature for Bartlett pears is between 29° and 31°. If the 

 air temperature where either of these fruits is stored rises 2° or 3° 

 above the upper limit mentioned, there is danger of increased decay 

 and undue ripening, the danger being greater the longer the period 

 during which the temperature is above 32°. For example, 3 or 4 

 days at 35° usually would have little or no effect, partly because of 

 a slower rise in the temperature of the fruit than in that of the air ; 

 :but 10 days at this temperature would probably shorten the life of 

 the fruit by about a week and possibly result in more decay. On the 

 other hand, if the temperature goes a degree or two below 29°, 

 there is a chance that freezing will occur. Celery and cabbage al- 

 lowed to remain too warm in storage may show yellowing and decay ; 

 potatoes are likely to begin to sprout if the temperature is too high 

 and usually become undesirably sweet if it is too low. Other com- 

 modities undergo these or other kinds of deterioration if the tem- 

 perature variations throughout long storage periods exceed the limits 

 given for them in this circular. In addition, there is always the 

 possibility that fluctuations in temperature will cause condensation 



