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No. 627 

 Cop. % 



\^jii\jUi/uf No. 627 



Forest Service Library 



November 1941 • Washington, D. C. 



UNITED STATES DEPARTMENT OF AGRICULTURE 



Fruit Pressure Testers and Their Practical 



Applications 



By Mark H. Haller, associate pomologist, Division of Fruit and Vegetable Crops 



and Diseases, Bureau of Plant Industry 



CONTENTS 



Introduction 



Description of various types of fruit pressure 

 testers 



Methods of making pressure-test determina- 

 tions 



Factors influencing pressure-test readings 



Variations in methods of making tests 



Maturity and ripeness of fruit 



Temperature of fruit 



Turgidity and moisture content of fruit _ . 



Fertilization 



Thinning and size of crop 1 



Page 

 1 



Factors influencing pressure-test readings- 

 Continued. 



Fruit size 



Fruit color 



Rootstock 



Application of pressure test to various fruits 



Apples 



Pears _. 



Peaches 



Plums 



Summary 



Literature cited 



Page 



^ WMM^MM 



INTRODUCTION 



The resistance of fruit, particularly apples, to pressure of the thumb 

 has long been used as an indication of ripeness. In 1917 a simple 

 method of more accurately measuring this resistance of fruit to inden- 

 tation was devised by Morris (50). 1 He used a marble partially 

 embedded in paraffin and resting on a spring scale. The test was made 

 by pressing an apple against the marble until the marble penetrated 

 the apple as far as the paraffin, and the pressure was read in pounds 

 from the scale. Lewis et al. (Jfi) developed a more elaborate instru- 

 ment, in which a cylindrical plunger was used with a lever and the 

 depth of penetration was regulated by electrical contact. This 

 principle was later used in a portable machine devised by Magness and 

 Taylor U8). Such instruments have been used commercially to 

 measure picking maturity and ripeness of apples and pears, and these, 

 with other types, have been used extensively in investigations to 

 measure the firmness of various fruits under experimental conditions. 

 Although various types of pressure testers have been used in experi- 

 mental studies on the various fruits, most of the studies and their 



1 Ttalic numbers in parentheses refer to Literature Cited, p. 17. 



407589° — 41 1 1 



