FRUIT PRESSURE TESTERS 7 



long seasons, but it might also be due to the difference in tempera- 

 tures at the time of ripening. 



The pressure tester has been used extensively in studies of the ma- 

 turity and ripening of fruit, but factors other than maturity may 

 influence the firmness of the fruit. 



Temperature of Fruit 



The condition of the fruit at the time of the test may also influence 

 the pressure test. Hawkins and Sando (37), using a needle plunger, 

 found that strawberries, raspberries, blackberries, and cherries re- 

 quired more pressure to puncture the epidermis at low temperatures 

 than at high. Rose et al. (56), using a %-inch plunger, found that 

 strawberries had a considerably greater resistance to penetration at 

 low temperatures than at high temperatures; however, with a 

 squeeze tester the difference, although statistically significant, was of 

 no practical importance. Using a plunger % inch in diameter, Hart- 

 man (32) found pears to be 3.4 pounds (10 percent) firmer at 51° F. 

 than at 97°. Hartman and Bullis (34), using a plunger 2 millimeters 

 in diameter, found the resistance to penetration of cherries to be nearly 

 30 percent less at 90° than at 32°. 



To determine the effect of temperature on the resistance to penetra- 

 tion of apples, duplicate 10-apple samples were removed from storage 

 at 32° F. and held at various temperatures from 80° to 32° for 3 to 6 

 hours. This was long enough to permit the fruit to attain approxi- 

 mately the temperature of the room but not long enough to permit 

 any appreciable ripening to occur. The pressure-test determinations 

 were made at room temperature (about 75°) and were completed for 

 each sample within 5 minutes after removal from the various tempera- 

 tures, during which time no appreciable change in the temperature of 

 the fruit occurred. That temperature of the fruit at the time of test- 

 ing had no significant effect on the pressure-test readings of apples is 

 shown by the data presented in table 1. The effect of temperature 

 on the resistance to penetration of peaches is not known. 



The results indicate that temperature may be an important source 

 of error and that the temperature should be controlled within some- 

 what narrow limits for some fruits, but that this is not necessary with 

 apples. 



Table 1 . — Relation of temperature to firmness of apples 



Temperature of fruil (°F.) 



33.5 

 40.5 

 48.5 

 55.5 

 68.5 

 77.0 









Pressure-test reading of— 







Rome 



Beauty 



Gallia Beauty 



Winesap 



Stay man 

 Winesap 



a i 



b i 



a i 



hi 



a i 



b > 



a' 



b' 



Pounds 



Pounds 



Pounds 



Pounds 



Pounds 



Pounds 



Pounds 



Pounds 



19.1 



19.3 



20.1 



19.6 



21.8 



21.9 



19.0 



19.3 



18.2 



19.1 



19.5 



19.1 



21.7 



22.0 



20.7 



19.0 



17.9 



19.5 



19.1 



20.2 



22.1 



22.6 



18.6 



19.1 



19.9 



19.7 



20.6 



19.7 



22.9 



22.4 



19.3 



19.3 



19.5 



19.0 



20.0 



19.7 



22.7 



23.2 



19.2 



18.9 



18.6 



18. 6 



19.5 



20.3 



22.9 



22.0 



19.5 



19.4 



1 



Aver- 

 age 



Pounds 

 20.0 

 19.9 

 19.9 

 20.5 

 20.3 

 20.1 



a and b represent duplicate 10-apple samples. 



