PHOSPHORIC ACID REQUIREMENTS OF YEAST. 197 



pelled to use very soft brewing liquor (i.e. deficient in lime), and 

 it is a common practice to counteract this evil by adding a little 

 powdered (unburned !) gypsum to the mashing liquor (about ijoz. 

 per 1000 galls.). Very satisfactory results are obtained : good 

 head, thorough fermentation, good " break " and a firm sedimental 

 yeast (provided the yeast employed is capable of furnishing such, 

 see vol. i. p. 256). We are indebted to H. SEYFFERT (I.) for an in- 

 teresting example, relating to a St. Petersburg brewery, working 

 with a liquor containing only 1.3 parts of CaO per 100,000. After 

 having failed to obtain satisfactory fermentation with a series of 

 pure yeasts, of German origin, it was finally decided to examine the 

 worts, and these were found to be deficient in lime, so that the 

 yeasts grown in them became more and more impoverished in 

 that constituent, as can be seen from the table (vol. ii. p. 196). 

 (The column headed CuO will be dealt with later on.) The yeasts 

 were famished in respect of lime, and even absorbed the small 

 quantities of that base present in the water with which they were 

 washed (vol. ii. p. 118). 



H. SeyfFert pushed his experiments to the furthest limit, by 

 reducing the already small lime content of the wort still more 

 by dialysis, before pitching it with yeast. In these circumstances a 

 highly frothy fermentation (vol. ii. p. 184) ensued. His observa- 

 tions have also a certain value in connection with the pure 

 culture of yeast, since they demonstrate that a successful result 

 depends not only on the happy selection of a suitable race of yeast, 

 but also on the favourable composition of the nutrient medium 

 a point already insisted on by HANSEN (III.)- Hence, in cases 

 where the application of pure yeast does not fulfil expectations, 

 one should not immediately condemn the innovation. The yeast 

 can only furnish good results when a suitable medium is provided 

 and this is the task of the practical man. 



259. The Phosphoric Acid Requirements of Yeast. 



Yeast requires a good deal of phosphoric acid ; and, as can be 

 seen from particulars already given, a considerable amount of this 

 acid is present in the ash. The figures given in the table on p. 1 93 

 agree with those reported by K. LINTNER (IV.) as obtained at the 

 Munich Experimental Station, and ranging between the limits of 

 3.21 and 3.84 percent, of P 2 5 (referred to dry matter), the mean 

 being 3.61 per cent. All these values, however, are surpassed by 

 59.5 per cent, of P 2 5 found in the ash of English top-fermenta- 

 tion yeast by A. C. SALMON and W. BE YERE MATHEW (I.). 



Under ordinary conditions in the brewery the needs of the 

 yeasts for phosphoric acid are satisfied by the phosphates and 

 organic phosphorus compounds present in the malt, though in 

 some cases the amount contained in the barley and malt is in- 

 adequate. As a rule, 0.9 per cent., calculated on the dry residue, 



