PREPARATION OF BURNT HAY. 169 



necessary heat is applied from outside, i.e. they are exposed to the 

 sun's rays, thus producing air-dried hay, or else the same result is 

 obtained by spontaneous heating, and therefore by the action of 

 the thermogenic micro-organisms dwelling on the plants. Here 

 again there are two possible methods of procedure, by following 

 one of which burnt hay is obtained. On this subject we are in- 

 debted to BOHMER (I.) for a critical research. According to him, 

 the mown grass is piled up into heaps about 10 to 13 feet high 

 and 13 to 1 6 feet in diameter, the mass being trodden down as 

 tightly as possible in order to prevent the admission of air which 

 might favour the development of mould into the interior. In 

 these heaps spontaneous heating goes on and becomes apparent, 

 often within twelve hours, but generally in twenty-four to thirty 

 hours. The operation is watched, and as soon as the temperature 

 inside the heap reaches 70 C. which is mostly the case in forty- 

 eight to sixty hours the heaps are opened and the contents spread 

 out thinly, a single turning being then sufficient to complete the 

 curing of the hay. By this fermentation, about which nothing 

 definite is known from the physiological point of view, not only 

 is the desired degree of dryness attained, but the hay also becomes 

 friable and acquires an aromatic odour. 



As mentioned above, the heaps must be opened when the 

 temperature has risen to 70 C., since, if this be neglected, the 

 spontaneous heating will quickly become spontaneous ignition. 

 If, as is possible, it is rainy when the hay is ready for spreading 

 out, such preliminary labour is futile. To this circumstance is 

 due the fact that burnt hay is seldom prepared, as also that, in 

 districts where the weather is too uncertain to allow of ordinary 

 haymaking being conveniently practised, another method of drying 

 has been developed, in which the necessary heat is likewise gene- 

 rated by a process of fermentation, from which a product known 

 as "brown hay" is obtained. This will be dealt with in the 

 Section on Lactic Fermentation. 



