INDUSTRIAL FERMENTATIONS 310 



{a) Rods (i) thermophilic, e.g. LactohaciUnshulyaricus, 

 L. delbrilckii, 

 (ii) mesophilic, e.g. L, casei. 

 (h) Cocci, e.g. Streptococcus lactis. 



(c) An intermediate group, e.g. Str. cretnoris which 

 gives some volatile acids (acetic and propionic) 

 in addition to lactic acid ; Leuconostoc citrovorum 

 (Str. citrovorus) and Leuc. dextranicum [Str. 

 paracitrovorus) which give volatile acids and 

 acetoin from lactic and citric acids. 



2. The Hetero fermentative or Pseudo-lactic Acid Bac- 

 teria which produce volatile acids, carbon dioxide and 

 hydrogen, as well as lactic acid, which rarely exceeds 

 half the sugar fermented. They exhibit surface grow^th on 

 liquid media, reduce nitrates and produce catalase. The 

 group includes organisms of the coli -aero genes type and a 

 number of pathogenic organisms. 



At the present time thermophilic organisms like 

 L. delhritckii {B. acidificans longissimus) or L. bulgaricus 

 are used to ferment the maltose and sucrose in molasses, 

 or glucose derived from the starch of potatoes, maize or 

 other cereals (which are first submitted to acid hydrolysis 

 or to the action of malt diastase), or the lactose in skim 

 milk or whey. The optimum temperature for fermenta- 

 tion is about 45° C, at which temperature the growth of 

 most contaminating bacteria, especially the butyric acid 

 bacteria, is inhibited. Yields of lactic acid of about 98 

 per cent., calculated on the sugar fermented, are obtained. 

 The sterilised mash, containing about 10 to 15 per cent, 

 of fermentable sugar, is inoculated under aseptic condi- 

 tions with a pure culture of the appropriate organism, 

 and fermentation allowed to proceed at the optimum 

 temperature, which is maintained by steam pipes dis- 

 tributed in the tanks. Calcium carbonate or lime is 

 introduced at intervals in order to maintain the solution 



