THt] WOl^K OF riWlTS ;^15 



fruits (e. g., Currant, Raspberry, etc.), a marked pro- 

 duction of acid. It is these fruits which are principally 

 used in the preparation of jams, jellies, etc. The 

 " jelling " depends on the presence of gelatinous sub- 

 stances (pectin compounds and allied substances) which 

 are present in the ripe fruit and are increased in 

 quantity by boiling the fruit; in this process, the acid 

 contained in the fruit acts on various substances and 

 transforms them into other substances which readily 

 " jell"; in the young fruit, these bodies, as well as the 

 acids, are lacking to such an extent that such fruits 

 can not be used for jelly- making. On the other hand, 

 they disappear from over -ripe fruit to such an extent 

 that it, too, is unfit for this purpose. 



Along with these changes which occur during the 

 process of ripening, go changes in the sugar -content. 

 The young fruit is either tasteless and insipid or else 

 acrid and sour; as it approaches ripeness, it gets 

 sweeter, and the sugar may accumulate to such an ex- 

 tent as to almost completely mask the taste of the acid 

 (which is, however, still present in undiminished 

 amount). The sweetness (and the characteristic flavor) 

 of the fruit is increased by dryness and warmth: 

 mountain -grown fruit is, for this reason, sweeter; over- 

 irrigated fruit is insipid. Sweetness may also be in- 

 creased in some cases by appropriate fertilizers, and, 

 even, in the case of oranges, by spraying the fruit with 

 chemicals. 



