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. 
