FRUIT 



167 



by a process of bottling, in which the fniit is placed in bottles 

 along with water with or without sugar, and sterilized by 

 heating with steam, or by making into jam. In the bottling 

 method, so long as bacteria can be prevented from obtaining 

 access to the fruit it will keep indefinitely. 



Jam and similar preserves are the result of preserving 

 fruit, even though it subsequently comes into contact with 

 air, and, therefore, bacteria. The object aimed at in producing 

 such a type of preserve is to obtain a solution of such strength 

 that even the hardiest bacterial .spores undergo plasmolysis. 

 For this purpose it is not the percentage composition of the 

 solution that is the determining point, but the molecular 

 concentration, and 26 per cent, of glucose will be equivalent 

 to 50 per cent, of cane sugar in producing a definite molecular 

 concentration. During the process of boiling jam, much of 

 the cane sugar is hydrolyzed, and the molecular concentration 

 of the liquid is therefore almost doubled. In Japan salt 

 is used for the preservation of fruit, and the French dried- 

 fruit industry is an important one. Fruit can be dried in the 

 sun, or by artificial heat. The gas industry is now supplying 

 suitable fruit-drying ovens heated by gas. Crystallized 

 fruit is produced by soaking the fruit in a saturated solution 

 of cane sugar. Many of these processes, however, depend 

 upon secret details, which often involve a limited amount of 

 fermentation to bring out special flavours. In spite of the 

 acid flavour of many fruits, a fair proportion of sugar is 

 always present as shown in Table 23. An apple, for example, 

 contains more sugar than a red beetroot. 



Table 23. — Sugar in Fruits. 



Apple .. .. .. .. .. 12 per cent. 



Apricot .. .. .. . . . . . . II 



Banana . . . . . . . . . . . . 20 „ 



Blackberry . . . . 6 „ 



Grape . . 8 to 26 per cent. 



Orange 6 per cent. 



Peach 8 



Pear . . . . . . o 



Plum . . ..13 



Raspberry . . . . . . 5 



Strawberry . . . . (> 



