YEASTS AND MOULDS 



51 



air, and thus secures anaerobic conditions favourable to the growth 

 of the lactic acid bacterium. This is an instructive example of 

 the way in which an organism may act beneficially by indirect 

 means. The mycoderma in question ferments dextrose but not 

 disaccharides. 



B. MOULDS 



It will not be necessary to enter into the classification of the 

 moulds, as only a few species are met with in dairy practice ; 

 the yeast-like forms, Monilia, Cladosporium and Oidium lactis, 

 and a few Penicillium species. 



1. Monilia and Cladosporium. Both of these groups reproduce 

 by budding, so that in young cultures they cannot be distinguished 

 from yeasts ; it is only at a 

 later stage that the cells be- 

 come elongated and form a 

 true mycelium which grows up- 

 wards into the air. The Monilia 

 group further resembles the 

 yeasts in being able to bring 

 about a true alcoholic fermen- 

 tation. A species which be- 

 comes black in old cultures, 

 Monilia nigra, will, according 

 to Burri and Staub 1 , form 

 deeply penetrating black spots 

 on the rind of hard cheeses. 

 On the other hand, the black- 

 ening of sour milk cheeses and 

 soft cheeses is due to Cladosporium herbarum, a mould which 

 is fairly prevalent in dairies 2 . A nearly related form, Clado- 

 sporium butyri, which is first white, then green, brown and 

 finally black, has been found by the author 3 to play an important 

 part in the development of rancidity in butter. Like several 

 of the mycodermse, it produces an ethereal fruity odour in milk, 

 but does not bring about alcoholic fermentation. The above- 

 mentioned Monilia and Cladosporium species liquefy gelatine, and 

 are able to grow in presence of large amounts of salt, so that their 

 growth in cheese is not inhibited by salting. 



2. Oidium lactis. This white mould is hardly ever absent from 

 any milk. It thrives better in cream than in skim milk, and 



1 " Landwirtschaftliches Jahrbuch der Schweiz," 1909, p. 487. 



2 This mould was first observed by Hers; (Milchzeitung, 1885). Adametz 

 has described several black moulds in his book, " Ueber die Ursachen und 

 Erreger der abnormalen Reifungsvorgange beim Kase" (Bremen, 1893). 



3 " Landwirtschaftliches Jahrbuch der Schweiz," 1901, p. 367. 



42 



FIG. 50. Monilia nigra,. (After Burri 

 - and Staub.) 



