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



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 30°. 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 

 of moisture on stored products, which in itself is undesirable because 

 it favors the growth of mold and the development of decay. 



Control of temperature is usually easier in large rooms than in 

 small ones if both are filled to capacity. This is because of the "fly- 

 wheel" effect produced by the larger mass of material, including 

 both the commodity and the building material. Refrigeration is thus 

 stored up, so to speak, and temperature changes occur more slowly. 

 For this reason small storage rooms generally will require closer 

 attention than large ones. 



Humidity of Storage Rooms 



The relative humidity of the air in storage rooms has a direct 

 relation to the keeping quality of the products held in them. With 

 only a few exceptions (see especially onions), the most desirable con- 

 dition is that in which the humidity of the air in the storage room 

 is kept at approximately the moisture content of the produce stored 

 therein. If it is too low, wilting is likely to occur in most fruits, 

 vegetables, cut flowers, etc.; if it is too high, it favors the develop- 

 ment of decay, especially in rooms where there is considerable varia- 

 tion in temperature. The exact control of humidity is rather diffi- 

 cult, however, and in the past was not often attempted in commercial 

 storage warehouses. However, at the present time new plants are 

 being designed and old ones changed over in such a way that a foun- 

 dation for humidity control in cold storage is being developed. 

 Sufficient refrigeration, whether coils or brine spray, is provided so 

 that the room can be operated with only a small difference in tern- 



