28 president's addkess. 



at some suitable speed was considered a fixed cliaracter of each 

 race of yeast-cells. It was thought that the cultivation of the 

 progeny of an individual possessed of this quality would produce 

 a race with the desired properties. In practice, bakers found 

 that it was impossible to continue the cultivation of a particular 

 strain of yeast, as the fermenting power appeared to undergo 

 deterioration. Ever\^ few weeks, a baker started a new stock of 

 yeast. Failure in maintaining suitable yeast by continued culti- 

 vation was ascribed to contamination of the stock by unsuitable 

 yeasts. When I started my study on yeasts for the Advisory 

 Council, I thought that my task was to isolate suitable races of 

 yeast-Cells and then to cultivate them under conditions which 

 would prevent contamination with uiisuitable yeasts. T hoped, 

 indeed, to isolate the strains that I needed by physiological 

 means rather than by bacteriological separation and the routine 

 examination of the progeny of hundreds of individuals, but I 

 did not imagine that I was going to find that any race of yeast 

 could be taught in a few days to ferment glucose quickly in a 

 baker's dough. Without going into details, I may say that I 

 found that any yeast of the species Saccharomyces cerevisics, 

 growing under certain conditions in a baker's wort, caused rapid 

 evolution of carbon dioxide in a dough. These conditions, as 

 far as I could define them, were a temperature less than that of 

 dough, aeration with a plentiful supply of air, the presence of 

 certain extractives from flour, the presence of certain substances 

 from hops detrimental to the growth of acid-forming bacteria 

 and a particular concentration of the sugar and other products 

 of malted starch. These conditions were so favourable to the 

 growth of yeast that in the bakehouse of the Technical College, 

 Sydney, Mr. F. Elliott was able to keep one strain of yeast for 

 making bread for almost six months. This yeast was so active 

 that two and a half ounces of the moist yeast ripened four 

 hundred and ten pounds of dough in six hours. If any of the 

 conditions in the wort were altered, the yeast rapidly became 

 quite unsuited for making bread. 



The manner in which the yeast is selected may be conceived 

 in two different ways. Each yeast-cell buds off' daughter-cells 



