CHAPTER XXVI. 



THE LACTIC ACID BACTERIA IN THE PREPARATION 

 OF FODDER. 



154. Brown Hay. 



ONE of the processes wherein micro-organisms play an active part for the pre- 

 servation of juicy fodder, viz., that dealing with burnt hay, has already been 

 noticed in 106; and we will now briefly sketch a second and more general 

 practice, viz., the preparation of brown hay. As in the former case, the warmth 

 necessary for driving off the water in the fodder has to be supplied by thermo- 

 genic bacteria. In addition to these, however, another series of organisms, 

 converting part of the carbohydrates into lactic acid, butyric acid, &c., comes 

 into play. The percentage of water in the green fodder employed for making 

 brown hay must be smaller than in that worked up into burnt hay. The 

 materials (grass, &c.) are built up into a round or square rick from 16 to 24 feet 

 in diameter, and 13 to 16 feet high, well trodden down, and thatched in thereof 

 to prevent the incursion of rain-water. At the end of about three days, spon- 

 taneous heating (" sweating ") will become manifest, and its progress can be 

 conveniently followed by means of a metal pipe laid in the stack and containing 

 a thermometer (provided with a couple of attached strings), which can be drawn 

 out as required, for the purpose of reading off the temperature prevailing in the 

 interior of the heap. In proportion as the temperature rises (generally up to 

 70 C., and frequently still higher), the mass begins to steam, and this goes on 

 for eight to fourteen days, a further four to eight weeks being allowed to pass 

 before the brown hay can be considered as finished. The product forms a firm, 

 dry mass, the colour of which, under normal conditions, is between pale and 

 dark brown, but is black when overheating has occurred. In point of cohesion 

 this brown hay is preferable to air-dried hay, being less brittle than the latter, 

 but tough and suitable for fodder. Its odour is aromatic, and recalls that of 

 freshly-baked bread or honeycomb. Comparative investigations into the chemical 

 changes produced in this method of preparation have been made by Dietrich, 

 Moser, Weiske, and others. The results obtained by Dietrich are given below 

 (see Table, p. 200), since they afford material for judging the process from the 

 Fermentation Physiologist's point of view. A parcel of aftermath was divided 

 into two portions, the one being worked up into withered (air-dried) hay, and 

 the other to brown hay ; and an average sample of each was subjected to analysis. 

 A comparison of the first and third lines of this table at once reveals the 

 high percentage of lactic acid and butyric acid in the brown hay, both of which 

 are entirely absent from air-dried hay. It will be evident, upon mature con- 

 sideration, that the production of these acids by bacterial activity does not occur 

 in the centre of the stack, since the temperatures (yo^go C.) prevailing there 

 are such as only the passive reproductive forms of these organisms are able to 

 withstand. To obtain a correct idea, we must picture the changes occurring 

 within the stack as proceeding in the following manner : the thermo-bacteria 

 develop in the centre of the mass and liberate heat, which radiates towards the 

 outside. Between this hot central layer and the external strata exposed to the 



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