PRESERVATION BY DRYING. 241 



tive changes going on in the hay. As a result of all three, the 

 temperature rises. 



This self-heating is utilized in some countries to cure the hay. 

 The grass is built up into a stack or rick 13 to 16 feet high, and 

 1 6 to 24 feet in diameter. It is well trodden down, but not firmly 

 packed, and the whole stack is thatched so as to shed the rain. 

 In such ricks a spontaneous fermentation sets up and the mass 

 becomes heated. The temperature frequently rises as high as 

 1 60 F., but not much higher, and there is no danger of spontaneous 

 combustion. The rick is not opened, but the hay remains in the 

 mass until the farmer wishes to use it. It is immaterial whether 

 the hay is rained on or not, and this makes the process especially 

 adapted to rainy districts. 



The fermentation which takes place in these ricks produces a 

 great change in the nature of the product. It becomes a firm, 

 dry mass, of a pale or dark brown color or, if the heating is too great, 

 it may be almost black. It has developed at the same time an 

 aromatic odor which resembles freshly baked bread. There 

 develops also a large amount of lactic and butyric acids, the amount 

 of lactic acid being as high as 7 per cent, and the butyric acid over 2 

 per cent. These acids are derived chiefly from the carbohydrates, 

 as is shown by the great reduction in the amount of these bodies in 

 the drying hay. A considerable part of the nitrogen material is also 

 lost, the total loss in the hay being about 14 per cent. This loss of 

 material is one of the objections to this method of curing hay. 

 It is known as brown hay. 



Sometimes a slightly different method is used. The freshly 

 mown grass is piled in heaps from 10 to 13 feet high, the mass being 

 trodden down as tightly as possible to prevent the admission of 

 air. The temperature in these heaps rises rapidly, and is tested 

 by a thermometer. When it rises to about 158 F., which occurs 

 generally in from 48 to 60 hours, the heaps are opened and spread 

 out in thin layers to the air. The heat in the hay now rapidly dries 

 the product and, with a single turning, it is ready for storing. Hay 

 thus prepared is called burnt hay, and develops an aromatic odor 

 which ordinary sun-dried hay does not possess. 



