INCIDENTAL PRODUCTS 293 



PRESERVATION BY DRYING 



The changes that are produced in fruit after it becomes 

 ripe are of two sorts; the first is chemical, the second bac- 

 terial. 



406. Chemical changes. In all cells certain chemicals 

 known as enzymes are present. These act on the substances 

 in the cells, producing changes in them. For example, some 

 enzymes in the muscles of animals cause softening of these 

 muscles after death while others break down the tissues and 

 bring about- a ripening of meat whereby it becomes tender. 1 

 Certain enzymes in fruits attack the carbohydrates or the 

 proteins, producing changes which destroy the value of the 

 product. If the fruit is to retain its natural flavor, the action 

 of these enzymes must be prevented. This can be done either 

 by heating or by drying. 



407. Bacterial changes. It has been seen that wherever 

 food, moisture, and warmth are present, bacteria are sure to 

 abound unless they have been previously killed or excluded. 

 To preserve fruit from bacterial action, therefore, it is neces- 

 sary either to remove the heat or the moisture. The former 

 process is cold storage; the latter, drying or evaporation. 



408. The fruit-drying industry. Where the climate* is 

 sufficiently dry to remove the moisture quickly, fruit is cured 

 by the simple device of laying it on trays out-of-doors. In 

 the case of common stone-fruits such as peaches and apricots, 

 the pits are first removed and the fruit then halved and 

 placed on trays in the sun. The trays are left exposed to the 

 sun for a period, then are gathered up, piled on small cars, 

 and run into air-tight buildings, called sulfuring houses. Here 

 the partially dried fruit is subjected to the fumes of burning 

 sulfur for periods varying from two to twelve hours, about 

 one pound of sulfur being used to a ton of fruit. This sulfur- 

 ing process is useful in two ways : It improves the appearance 



1 Marshall's Microbiology. 



