CIRCULAR 6 00, U. S. DEPT. OF AGRICULTURE 



the individual fruits. This subject has a bearing on the problem under 

 consideration, as it is necessary to have a common starting point in 

 designating the time required to effect complete disinfestation. 



Thermocouples were employed to determine the rate of cooling 

 under the conditions of the present experiment. The only departure 

 from the conventional set-up was the manner in which the constantan 

 and copper wires were joined and placed in the fruit. To provide a 

 known junction point, the wires were soldered together at the tip ends 

 instead of being twisted, as is customary. Then by threading either 

 the copper or constantan portion in a needle, it was possible to pierce 

 the fruit readily and bring the junction at or very near the center of 

 the fruit. No. 30-B. and S.-gage constantan and No. 32-gage copper 

 were used. Diagrams of the set-up are given in figure 1. 



The rate of fruit cooling in an air temperature of 36° F. is shown in 

 figure 2. Almost identical curves were obtained at 32°. As pointed 

 out by Rose, Wright, and Whiteman, 4 " although it is known to be 



■ AIR TEMPERATURE 



-FRUIT TEMPERATURE AT TOP OF BASKET 



■FRUIT TEMPERATURE AT CENTER OF BASKET' 



60 70 80 



TIME (HOURS) 



20 30 



Figure 2. — Rate of fruit cooling in an air temperature of 36° F. 



120 210 



only approximately correct, * * * the rate of temperature drop 

 at any given time during cooling is proportional to the difference be- 

 tween room temperature and fruit temperature at that time." The 

 data in figure 2 show that, whereas the apples at the top of the basket 

 appeared to cool to air temperature eventually, those at the center 

 were still about 0.7° above after 215 hours. In the present case this 

 difference in temperature is attributed to heat of respiration 4 5 . Rose 

 and coworkers calculated the amount of thermal energy produced in 

 respiration by apples at 32° as ranging between 660 and 880 B. t. u. per 

 ton of fruit in 24 hours. In gravity air-circulation systems the heat 

 generated by the fruit is apparently not removed at a sufficiently 

 rapid rate to allow the fruit in the interior of the package to attain air 

 temperatures. In view of this situation, if the starting point in disin- 

 festation schedules is to be based on the temperature of the fruit, it 

 may be desirable to indicate a temperature slightly above air tempera- 



* Rose, Dean H., Wright, R. C, and Whiteman, T. M. the commercial storage of fruits, vege- 

 tables, and florists' stocks. U. S. Dept. Agr. Cir. 278, 40 pp. 1933. 



« Griffiths, Ezer, and Awbert, J. H. the heat generated bt fruit. [Gt. Brit.] Food Invest. Bd 

 Rpt. 1927: 88-90, illus. 1927. 



