122 MICRO-ORGANISMS AND FERMENTATION. 



which manifests itself as follows : The liquid gradually loses 

 its brightness, and when it is agitated filaments of a silky 

 lustre rise from the bottom, and the beer assumes a disagree- 

 able odour and taste. According to Fellowes, this species 

 is also found in English beer. It does not always react on 

 the beer, probably on account of the larger amount of hops. 

 In cultures, the bacillus develops either in the presence or 

 absence of free oxygen. In nutrient liquids it ferments 

 carbohydrates, and amongst them the saccharoses, without 

 previously inverting them. Amongst its fermentation pro- 

 ducts, lactic acid, acetic acid, and alcohol predominate. The 

 acids produced cause the precipitation of nitrogenous com- 

 pounds in the liquid, and these, mixed with the bacilli, produce 

 a cloudiness, consisting of lustrous filaments. The nutritive 

 mixture best suited to this bacterium is an extract of malt 

 mixed with agar and a small quantity of alcohol, or, still 

 better, neutral or slightly alkaline sweet wort. 



If this bacterium is exposed to a temperature of 55-60 C. 

 in beer, it is soon killed. Henneberg has closely investi- 

 gated both this species and two other lactic acid bacteria 

 occurring in beer which cause the same disease Saccharo- 

 bacillus Past., var. berolinensis and Bac. Lindneri. These all 

 occur as thin and comparatively long bacilli, either straight 

 or curved, and usually cluster together. In hanging drops 

 they form very long threads. From a physiological point of 

 view they behave quite differently. Saccharobacillus Past. 

 gives the most vigorous formation of acid in arabinose and 

 trehalose, weaker in saccharose, maltose, dextrose, laevulose, 

 and galactose. Its optimum for acid formation lies between 

 24 and 33 C. The variety berolinensis gives a weaker yield of 

 acid, and none at all in raffinose and trehalose. Its optimum 

 for acid formation is at 20-24 C. According to Henneberg 

 it is this species in particular which grows in Berlin " Weiss- 

 bier," and imparts to it its peculiar character. Other varieties 

 of lactic acid bacteria occur, however, in this kind of beer. 



Bac. Lindneri produces acid in maltose, and to a small 

 degree in dextrose. The optimum for acid formation is at 

 17- 18 C. This species or variety frequently occurs in 

 ordinary lager beer, and influences its flavour and aroma, 



