DESICCATION, EVAPORATION AND DRYING OF FOODS 521 



stances dissolved in the water may be actually antiseptic when concen- 

 trated, as the acids of the juices of certain fruits. More often the 

 sugars reach a concentration so great as to prevent growth by plasmo- 

 lyzing the cell contents of the organism. For every organism there is a 

 maximum concentration reached sooner or later beyond which growth 

 is impossible. 



Dried foods may be divided into three groups using the relative 

 abundance of carbohydrates, fats, and proteins, as the basis 

 of classification. 



Carbohydrate foods are usually preserved by drying. Many, such as 

 grains and nuts and the flours and meals prepared from .them, do not re- 

 quire artificial heating. They are, however, somewhat hygroscopic and 

 in damp climates enough moisture is taken up to allow the growth of 

 injurious molds and bacteria. Still other carbohydrate food stuffs 

 require more or less care in the drying or curing, such as hay and fodder 

 in general. These are usually dried by exposure to the air and sun 

 until most of the water has been evaporated. Fodder that has become 

 moldy through the presence of too much moisture is the cause of trouble 

 in horses and less frequently in cattle. Many deaths due to the so- 

 called cerebro-spinal meningitis in the horse are frequently due to the 

 consumption of moldy hay. In localities where the air is too moist or 

 rains so frequent as to make it difficult to dry hay, curing is effected 

 by a process of self -fermentation. The hay is piled in a mass while 

 still green and undergoes a process of heating. The temperature rises to 

 about 70. The cause of this rise is somewhat uncertain but is probably 

 due to the combined action of enzymes and microorganisms. Just how 

 much of the keeping quality is due to the heating, how much to the loss 

 of water, and how much to the accumulation of products of fermenta- 

 tion is uncertain. In other cases the heated hay is spread out and 

 quickly dried sufficiently so that it may be stored. A certain small 

 percentage of the nutriment in the hay is necessarily lost in the develop- 

 ment of the heat. 



Many vegetables in desiccated form can now be bought upon the 

 market, and have been prepared in recent years in large quantities for 

 household use by the housewife. Fruits are also quite generally pre- 

 served by drying. In many instances, as in peaches, apples, and berries, 

 it is probable that enough moisture is removed to prevent organisms 

 from growing, but in many other cases, as in the preparation of currants 



