EXAMINATION OF YEASTS 239 



growth, but differing from them in not giving rise to spores 

 even when cultivated under the most diverse conditions. 

 The torulce produce little or no alcohol when grown in 

 saccharine liquids. To this group belong the Saccharo- 

 myees rosaceus, niger and albus, the pink, black and white 

 torula respectively that are frequently met with in the air. 



Examination of Yeasts. — Hansen, to whom the present 

 scientific aspect of the fermentation industries is due, 

 elaborated a scheme for the examination of the saccharo- 

 mycetes, which depends upon the isolation of a pure 

 culture, and the observation of the temperature and time 

 they take to form ' ascospores ' and ' films.' 



The importance of this method of investigation will be 

 apparent when applied to the examination of brewery yeast 

 to determine the presence of disease or ' wild ' yeasts, which 

 are the cause of such diseases as muddiness, ropiness, 

 bitter or acid taste, which render the beer undrinkable, or 

 injure its keeping properties. Starting with pure yeast, 

 thorough cleanliness, and means of keeping the beer free 

 from ' wUd ' yeasts and other organisms, beer may be pre- 

 served both bright and clear, even though the temperature 

 be comparatively high. To obtain pure yeasts, it is first 

 necessary to take a single cell, and from this to grow a 

 series of cells in sterilised beer-wort, to break this up into 

 different portions of seed-material, from which other crops 

 are produced, and so on, until a sufi&cient quantity of pure 

 yeast is produced to bring about the necessary fermentation 

 in a large bulk of wort. 



The characteristic appearance which at one time was 

 thought to belong to the yeast-plant has been shown by 

 Hansen to have no existence, except in a very limited sense. 

 Throughout the entire series of Hansen's researches the 

 leading idea obtains — namely, that the shape, relative 

 sizes, and the appearances of the cells, taken by them- 

 selves, are not sufficient to characterise a species. The 



