2 CIRCULAR 5 7 9, U. S. DEPARTMENT OF AGRICULTURE 



As will be seen from these definitions, the stage of ripeness of the 

 fruit is based primarily on firmness, although flavor is also consid- 

 ered, and the terms are presumed to indicate the potential life of 

 the apples. In these definitions the distinctions between the 

 stages are not very sharp ; for example, the main distinction between 

 "hard" and "firm" is that in the firm apples the flesh is "tenacious but 

 becoming crisp" instead of "tenacious," and the flavor is "slightly 

 starchy" instead of "starchy." Inspectors may differ in their opin- 

 ions as to whether the tenacious flesh of a lot of apples is becoming 

 crisp and whether the flavor is starchy or only slightly so. Thus, 

 the ripeness rating may depend considerably on personal judgment. 

 Likewise, a lot of apples may have a tenacious flesh and would rate 

 "hard" according to firmness but be entirely lacking in starchiness 

 and would rate "firm ripe" according to flavor. Such a lot would not 

 comply with any of the definitions and might be rated "hard" or "firm 

 ripe," depending on whether the inspector gave primary considera- 

 tion to firmness or to flavor. 



Because of the possibilities of errors in designating ripeness, due 

 to the inexactness of the definitions and the personal equation, it is 

 extremely desirable to establish some more definite means of deter- 

 mining ripeness, regardless of the month or the season of the year 

 and the conditions under which the fruit was grown. The object of 

 this investigation was to ascertain whether the firmness as determined 

 by pressure test could be used for this purpose. 



The definitions for the degrees of ripeness to some extent indicate 

 the changes that occur in the apples during ripening. One of the 

 principal changes is the softening of the fruit from the tough or 

 tenacious condition of the hard stage through the crisp, juicy condi- 

 tion of the firm-ripe stage to the mealy and dry condition associated 

 with the ripe and overripe stages. This softening of apples after har- 

 vest has been found by Haller 3 and others to be associated with hy- 

 drolysis of the insoluble protopectin to a soluble pectin. The proto- 

 pectin cements the cell walls together, and its conversion to a soluble 

 form results in softening of the fruit as the cells become more easily 

 broken apart and ruptured. 



The hydrolysis of starch to sugar is another important change that 

 occurs during ripening of apples. Thus, the starchy taste of "hard" 

 fruit is lost with a corresponding increase in sweetness. However, 

 the amount of starch present may vary greatly, depending on the 

 variety and growing conditions. During ripening there is generally 

 a decrease in acidity with a corresponding loss of sourness. Acidity 

 also may vary greatly with variety and growing conditions, conse- 

 quently the sweetness or lack of sourness may not indicate the degree 

 of ripeness. Other important changes may occur in the aroma, en- 

 zymes, and other minor constituents of the apple during ripening, 

 but relatively little is known concerning these factors. 



As apples develop on the tree they reach a point at which they are 

 considered mature. At this point they have accumulated sufficient 

 reserves or developed certain characteristics so that they will become 

 mellow and have normal flavor for the variety after being: removed 

 from the tree. As used m this circular the terms "maturity" and 



3 Haller, M. H. changes in the pectic constituents of apples in relation to soften- 

 ing. Jour. Agr. Res. 39 : 739-746, illus. 1929. 



