FERMENTATION. 



109 



at a temperature of 23° C, most slowly (seventeen days) at 3° to 4° C, 

 and cease to be formed at 29° C. and at .5° C. 



This yeast gives rise to neither cloudiness nor to any 

 unpleasant bitter taste. It secretes an invertase and causes 

 fermentation of all the carbo-hydrates that are fermented by 

 the other yeasts of this group. In old cultures of the films 

 the cells are small, very irregular in shape, and thread-like, 

 like the preceding. 



6. Saccharomyces Pastorianus III. (Hansen) is, according 

 to Hansen, one of the causes of turbidity in beer. Grown on 

 yeast water gelatine at a temperature of 15° C, at the end of 

 sixteen days the colonies present peculiarly fringed edges ; 

 grown in wort it gives rise to a top fermentation, and causes 

 considerable turbidity with a production of alcohol and 

 carbonic acid gas. 



The spore formation is very much hke that in the preceding species ; it takes 

 place most rapidly (twenty-eight hours) at 25° C, most slowly (nine days) 

 at 8.5° C, and ceases at 29° and at 4° C. The film appears in the form of 

 small flakes most rapidly (seven to ten days) at 26° to 28° C, most slowly 

 (five to six months) at 3° to S°, and ceases altogether at 34° and 2°. Here 

 again the elongated or sausage form predominates, but large and small 

 rounded and oval cells are also present in the sedimentary forms in the 

 films at from 20° to 28° C. The cells are of much the same shape as are those 

 of the sedimentary yeast, but at a temperature of from 15° down to 3° C. 

 there are elongated mycelial-like threads which in old cultures become still 

 more characteristic. These mycelial-like threads are developed at the 

 above temperature, which is much lower than in the case of the threads in 

 Saccharomyces Pastorianus I., where they are most characteristic at a 

 temperature of 13° to 15° C. At the same temperature, 15° to 3° C, the 

 cells in Saccharomyces Pastorianus II. are oval and rounded. 



Hansen describes in less detail a number of other ferments 

 which produce alcohol from sugar. 



7. Saccharomyces Ludwtgtt, though found in the sap of 

 oaks, grows freely in yeast water, when it appears as a peculiar 

 caseous mass or as fungus-like specks which float in the 

 fluid. One great peculiarity of this form is that it may be 

 so modified by cultivating it in- beer wort through several 

 generations at a temperature of 25° C. that it does not form 

 spores, or that it forms them but slowly. The spores, 

 when formed, are usually from one to four in number, but 

 there may be more ; the cells of the film are usually con- 

 siderably elongated. The film formation goes on most 

 rapidly at about 25° C. ; at the ordinary temperature of 



