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 like 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 5, 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 Ludwigti, 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 



