TECHNICAL MYCOLOGY. 



SECTION XIII. 

 YEAST NUTRITION AND YEAST CULTURE. 



CHAPTER XLIX. 



MINERAL FOODSTUFFS. 



257. Ash Content and Ash Analysis. 



SINCE the requirements of the Eumycetes in general in respect of 

 ash constituents have already been fully dealt with in chapter xli., 

 it may seem superfluous to the reader to revert to the question of 

 the mineral needs of the yeasts, all of which belong to that group. 

 It should, however, be remembered that the matter was then 

 treated from a purely physiological standpoint, the problem being 

 to ascertain what mineral substances are essential t > the structure 

 of the Eumycetes, and therefore also yeasts. The question, 

 however, comes into the region of practical economics, so soon as 

 we have to deal with ferments (e.g. yeasts) that are required in 

 large quantities for industrial purposes. In this case it is no 

 longer sufficient to know that certain ash constituents are indis- 

 pensable, but it also becomes necessary to ascertain how these 

 requirements can be satisfied in practice, and to investigate the 

 conditions under which the activity of these ferments can be 

 raised to the maximum by a suitable selection of the sources of 

 supply of the mineral foodstuffs under consideration. 



From this practical standpoint we shall deal more fully, in the 

 present chapter, with three elements : calcium, phosphorus, and 

 sulphur, which have been, up to the present, more fully investi- 

 gated than any others with regard to their influence on the develop- 

 ment and activity of yeast. On the other hand, our knowledge 

 on the importance of potassium must be characterised as scanty, and 

 therefore this foodstuff (also known to be essential) must neces- 

 sarily be dismissed in a few words. From experiments conducted 

 by H. BECKER (I.) it appears that the quantity of potash in the 

 nutrient solution influences the degree of attenuation . A beer wort 

 containing naturally 0.071 per cent, of potassium (K), attenuated 

 to 56.4 per cent., whereas in the case of two parallel samples, the 

 potassium content of which was raised to 0.078 and 0.085 per 

 cent, by the addition of potassium carbonate, attenuated, under 

 VOL. u : PT. 2 191 N 



