2 3 o CULTIVATION AND REPRODUCTION OF YEAST. 



and is determined by numerous factors, more particularly the 

 age of the cells and the conditions of its earlier life. Hence both 

 the fecundity and reproductive power differ, under identical 

 external conditions, with the species (or race) of the yeast. On 

 this point P. LINDNER (XX. and XIV.) in 1889 instituted com- 

 parative experiments with twenty-two beer yeasts and fifteen white 

 beer, spirit and pressed yeasts. The former, sown in 650 c.c. of 

 hopped wort (11.95 Balling), furnished from 4.3 to 12 grins, of 

 crop, weighed after pressing, whilst the yield from the second 

 group, sown in 1350 c.c. of wort, was 9.3 to 19.5 grins. The 

 highest yield was obtained from the white-beer yeasts, the pressed 

 yeasts coming second. Further contributions on this matter have 

 been published by F. SCHONFELD (I.), 0. SOLDAN (I.), F. HESS (I.),. 

 RODERICK MEISSNER (I.), G. KORFF (I.), W. KNECHT (I.), and 

 others. 



The influence of the age of the sowing on the reproductive 

 capacity and reproductive power was examined by M. ELLIESEN (I.) 

 in the case of Frohberg and Logos yeasts. Some of his results 

 are given below : 



With increasing age the vitality and reproductive power of the 

 cells are weakened. Whilst the gradual thickening of the cell 

 membrane is a good defence against adverse influences on the 

 part of a nutrient medium that is changed for the worse, it 

 equally presents obstacles which must be overcome by the stimu- 

 lating ingredients of a fresh medium before the sowing can 

 reproduce itself and lay up new material. The far higher repro- 

 ductive capacity of the day-old sowing in the above table is 

 therefore not surprising. 



An important point in fermentation technology is the influence 

 of the extent of the sowing on the amount of crop that can be 

 produced in a nutrient medium of given quantity and composition. 

 This applies to the brewer and vintner, as well as to the yeast 

 manufacturer. The first reliable determinations obtained under 

 practical working conditions were those of THAUSING (I.), who insti- 

 tuted parallel experiments in four Austrian breweries (A to D), 

 the wort being pitched with 0.33, 0.5 and 0.66 litre of thick low- 



