barrett] THE MOST USEFUL HOUSE PLANT 19 



fermentation in the same way. It is impossible that any whole 

 plants should survive this rough treatment and should afterwards 

 grow and ferment ; but in order to make sure that not even living 

 bits of them escape, an antiseptic has been used which stops the 

 action of living matter on sugar. As this has been proved not 

 to interfere with the process, evidently the cause of alcoholic 

 fermentation is a substance which is not alive, although it is 

 produced by a living organism. It has been named zymase, and 

 it is only one of several ferments found in this tiny plant. The 

 others may help in this process or may work upon the protein 

 (nitrogenous) matter of the dough. 



If then its growth is not the cause of alcoholic fermentation, 

 why are we so particular to give yeast the best conditions for 

 reproduction ? 



Because, since zymase is produced by living plants, any increase 

 in the number of these will lead to an increase in the quantity of 

 the ferment and so in the amount of action produced. 



Now let us compare the alcoholic fermentation which we have 

 seen in its simplest terms with that which takes place in dough. 

 The water of the experiment is represented by water, warmed to 

 start the action, or by the water in milk. The molasses corres- 

 ponds partly with the sugar, if any, partly with the sugar of the 

 milk and partly with the carbohydrates of the flour. These 

 consist of a little sugar and a large amount of starch. Starch, 

 we found, is not acted upon by yeast; but unfortunately flour 

 contains a ferment of its own called, diastase, which combines 

 starch with water, making it into the particular kind of sugar best 

 for the yeast. For that matter neither molasses nor any one of 

 our ordinary sugars is exactly right for yeast. It has to change 

 that sugar by another ferment which it contains, before zymase 

 can begin to work. 



There are a number of other substances involved in the making 

 of dough. Wheat flour, besides its 76 per cent of starch and 

 sugar, contains in small amounts water, gluten and other proteins, 

 fats and oils, mineral substances, ferments and the inevitable 

 bacteria. Gluten forms the tough but elastic part of the dough. 

 If it were not for this the bubbles of gas would break through the 

 surface of the loaf and the bread would fall. The stronger the 

 gluten of a flour the more yeast is necessary to raise it. Upon it 

 more than any other one thing depend the quality and flavor of the 



