2 CIRCULAR 62 7, U. S. DEPARTMENT OF AGRICULTURE 



practical applications have dealt with apples, pears, peaches, and 

 plums, and with the use of the United States Department of Agricul- 

 ture (Magness and Taylor) or the Oregon-type instrument with a 

 plunger having a diameter of % 6 or %<$ of an inch. Since these results 

 are scattered through various publications, the purpose of this circular 

 is briefly to describe the pressure testers, to indicate their applica- 

 tions and limitations, and to summarize in one place the widely 

 scattered data concerning them. 



DESCRIPTION OF VARIOUS TYPES OF FRUIT PRESSURE 



TESTERS 



The type of pressure tester described by Magness and Taylor (4.8) is 

 shown in figure 1, as modified and manufactured at the present time. 

 The apparatus consists of a cylindrical metal barrel within which 

 works a plunger attached to the barrel by a steel tension spring. A 

 groove is cut in the barrel to show the plunger sleeve. The calibra- 



■ 



lif 



Figure 1. — Fruit pressure tester for apples, pears, and peaches. (Photograph 

 through courtesy of R. Schneider.) 



tion in pounds of the pressure required to force the plunger back is 

 marked on the barrel at the side of the groove. An indicator slide 

 that is pushed back by a screwhead on the plunger sleeve loosely en- 

 circles the barrel. The pressure-test reading is made at the edge of 

 the indicator slide nearest the plunger. A slightly rounded plunger 

 tip screws into the outer end of the plunger and holds a splash plate 

 in place between the plunger tip and the plunger. The purpose of the 

 plate is to protect the operator from any juice that may squirt out 

 from the fruit being tested. The plunger tip has a mark around it to 

 indicate the proper depth of penetration. 



In the tester as originally described by Magness and Taylor the 

 depth of penetration of the plunger was indicated by electrical con- 

 tact with a flashlight and the reading was made directly. The 

 apparatus as now manufactured differs from the original in that the 

 depth of penetration is determined by the line around the plunger 

 and the reading is made from the indicator slide. 



Blake (9) described a pressure tester for use with peaches similar 

 to that described by Magness and Taylor (48) except that the plunger 

 rod extends through both ends of the barrel and the instrument has 

 an indicator slide. He tried plungers having diameters of K 6 , Ke, 

 3 /{ 6 . and 3 7(ooo of an inch. 



