4 CIRCULAR 713, U. S. DEPARTMENT OF AGRICULTURE 



If the shipments arrive at market in good condition but, after 

 being unloaded, have to be held on a pier or in a receiver's" ware- 

 house or storeroom during severely cold weather, the danger that 

 they may freeze depends on (1) the quantity of the fruits or vege- 

 tables to be stored and their temperature before exposure to the 

 conditions where they must be held, (2) the amount of artificial 

 heat provided, (3) the tightness and insulating quality of the pier 

 or warehouse construction, (4) the temperature of the storage 

 space during the previous day,, and (5) the quantity of other 

 commodities held in the storage space and their capacity for 

 retaining heat. 



Additional facts that should be kept in mind in attempting to 

 prevent freezing are (1) produce cools more slowly if packed 

 tightly than if packed loosely and more slowly in tight boxes, bas- 

 kets, or barrels than in slatted crates or hampers; (2) certain 

 produce (pears, apples, and citrus fruits) cools more slowly if 

 wrapped than if not wrapped; (3) close stacking of packages 

 gives some protection from freezing; (4) the bottoms. of outside 

 stacks need the most protection because freezing occurs there first ; 

 (5) sawdust along the bottoms of outside doors helps to keep cold 

 air out; (6) a covering, such as a tarpaulin, over the stacks and 

 tucked carefully around them, especially at the bottom, helps to 

 retain both the heat already present in the produce and that which 

 it produces by virtue of being alive (heat of respiration) . 



Even if there is no permanent equipment for heating the room 

 or pier, substantial help in keeping up the air temperature can be 

 obtained by setting barrels, oil drums, or buckets of hot water 

 under the tarpaulins where heat is most likely to be needed. Since 

 water will freeze before any of the fruits or vegetables do, the 

 heat it gives up on freezing is available for further protection. The 

 heat that could be furnished by a lighted lantern, an oil heater, or 

 a container full of hot water set under a tarpaulin covering stacks 

 of produce might seem small, but it might be just enough to keep 

 the produce from freezing. The beginning of ice formation on 

 water in a container can be taken as a sign that the surrounding 

 temperature is becoming dangerously low. It should be remem- 

 bered, however, that the heat given up by the water as it freezes 

 can help to protect the produce until all the water is turned to ice. 

 Care should be taken, of course, that overheating does not occur. 



LENGTH OF TIME REQUIRED FOR FREEZING TO OCCUR 



Because of qualifying factors already mentioned (p. 4) it is 

 not safe to make general statements concerning the time required 

 for fruits and vegetables to freeze in a place where the air tem- 

 perature is below 32° F. Even if surrounding conditions were 

 identical there might still be differences in freezing time, because 

 of differences in varieties or kinds, in maturity of the commodity, 

 and in its freshness. Freshness would be important chiefly in 

 connection with leafy crops such as spinach, lettuce, and kale. 



In order to obtain information on freezing under specific condi- 

 tions, single commercial packages of 4 kinds of fruit and 23 kinds 

 of vegetables were held at 14° to 25° F. until freezing occurred in 



