FERMENTATION OF BREAD 125 



disintegrated as in many fermentations. The bacterium is a coccus with 

 fixed planes of division, and, like the alga Nostoc, forms unbranched rosary- 

 like chains embedded in jelly. Cane and grape sugar are necessary for 

 the production of the mucilage. In media containing neither of these 

 carbohydrates, the organism grows as a simple Streptococcus, without any 

 capsule. 



In bread-making (101), too, we cannot dispense with the help of micro- 

 organisms, which are important agents in the conversion of the nutritious 

 wheat meal into a tasty bread. Yeast, as used by bakers, consists of 

 a mixture of Saccharomyces cells (the alcohol ferment), and of different 

 species of bacteria. The bacteria, to some extent, prepare the starch for 

 the yeast by enzymes, and contribute to the taste of the bread by the 

 organic acids (lactic and acetic) they produce. The fermentation set up by 

 the yeast gives rise, per kilogram of bread, to about 2-5 grm. alcohol and 

 3-7 grm. C0 2 - This gas it is which causes the bread to 'rise,' and the 

 inflation is of course increased by the expulsion of alcohol vapour and 

 steam, which takes place in baking. Some of the fermentation products 

 finally remain in the bread and affect its taste. 



