DISTILLERY AND BREWERY MASH. 121 



not a few of the numerous species described must be regarded 

 as sub-species of a certain parent form. 



Thus Beijerinck takes, as the parent form of Leichmann's 

 species, Bac. DelbriicJd, a very vigorous acid producer Lacto- 

 bacillus fermentum, a young culture of which prepared at 

 37 C. for 36 hours in an acid mash, and then transferred to 

 wort jelly (gelatine agar), forms very small transparent colonies 

 consisting of motionless bacilli of different lengths together 

 with micrococci. In wort it forms threads of different lengths. 

 The smaller the amount of oxygen present the more extended 

 are the cells. Its optimum for the production of acid is 

 41-42 C., and at 50 C. it ceases to develop acid. According 

 to Beijerinck this parent form may be converted into Bac. 

 Delbriicld through a continued series of cultivations with free 

 access or air at 48 C. (well above its optimum for acid pro- 

 duction), and then transferring to wort jelly at 37 C. 



In the distillery, Lafar, Leichmann and the author (in 

 1896), and more recently Kusserow and others, have introduced 

 into practice pure cultures of predominant species occurring 

 in normal sour mash (Bac. acidificans longissimus, Bac. Del- 

 briicki), with the object of regulating the souring of the mash. 

 By the proper application of such cultures in distilleries and 

 yeast factories, and at the same time securing a uniform 

 temperature of acidification throughout the whole mash, it 

 is possible to absolutely prevent the development of foreign 

 and harmful bacteria. 



In the brewing industry the lactic acid fermentation takes 

 place in malting, and in particular in mashing. Accurate 

 investigations were made by Prior. Some lactic acid is also 

 formed during fermentation. Lactic acid is formed in large 

 quantity in Belgian beers prepared by " spontaneous fer- 

 mentation," imparting a sharp taste. " Weissbier " owes its 

 refreshing taste to a vigorous lactic acid fermentation. In 

 modern low-fermentation breweries attempts are made to get 

 rid, not only of lactic acid bacteria, but also of bacteria of all 

 kinds from the fermentation. 



The Saccharobacillus Pastorianus described by van Laer, 

 which occurs in the form of rods of different lengths, produces 

 a characteristic disease (" tourne ") in weakly hopped beer, 



