BACTERIA AND FERMENTATION 



135 



Saccharomyces pastorianus I. is a low fermentative yeast 

 in elongated cells, producing a bitter taste to beer and an 

 unpleasant odour. It can also produce turbidity. 5. pastor- 

 ianus III. produces turbidity, and 5. ellipsoideus II. has a 

 similar effect. 



In 1883 Hansen demonstrated that the much-dreaded 

 turbidity and disagreeable tastes and smells in beer may be 

 due to mixture of two yeasts, each of which by itself gives 

 a faultless product. 



Industrial Application of Bacterial Ferments. From what 

 has been said we trust it has been made evident that bac- 

 teriology has a place of ever-increasing importance in regard 

 to fermentative processes. Not only have the caus'al agents 

 of various fermentations been isolated and studied, but from 

 their study practical results follow. The question of pure 

 cultures alone is one of practical importance ; the recognition 

 of the causes of " diseases " of beer is another. 



We cannot enter into a full discussion of the role of bac- 

 teria in industrial processes, but several of the chief directions 

 may be pointed out. Without exception, bacteria have a 

 part in them on account of their powers of fermentation. In 

 securing their food, bacteria break down material, and bring 

 about chemical and physical change. The power which 

 organisms have of chemically destroying compounds is in 

 itself of little importance, but the products which arise as a 

 result are of an importance in the world which has not 

 hitherto been recognised. We have used bacteria abund- 

 antly in the past, but we have not perceived that we were 

 doing so. The maceration industries may be mentioned as 

 illustrative of this use without acknowledgment. The flax 

 stem is made up of cellular substance, flax fibres, and wood 

 fibres ; the later are of no service in the making of linen, but 

 the whole is bound together by a gummy, resinous sub- 

 stance. Now this connective element is got rid of in the 

 process of retting. There is dew-retting and water-retting. 



