462 MICROBIOLOGY OF SPECIAL INDUSTRIES. 



Where leaven made from old dough is used, as in most parts of 

 Southern Europe, the part of bacteria in the fermentation is much 

 greater. 



The bread has a thicker and firmer crust, a fuller flavor and a distinct 

 acidity which is often excessive. It holds its moisture well and keeps 

 for a week longer. 



The making of so-called French bread, as it is carried out in Paris, is 

 a successful attempt to combine the good qualities of the above extremes 

 and to avoid their defects. It is based on the fact that where a leaven 

 consisting of a mixture of yeast and bacteria is used, the yeast develops 

 more rapidly at the beginning and the bacteria at the end. By successive 

 additions of flour and aeration by repeated kneading, sufficient yeast 

 growth is obtained to make the bread light and the bacteria kept within 

 the limits necessary for flavor and keeping qualities without causing undue 

 acidity. 



VEGETABLES. Various vegetables, cabbage (sauerkraut), string- 

 beans, cucumbers, etc., can be preserved by covering them with weak 

 brine and allowing them to undergo spontaneous fermentation out of 

 contact with the air. 



The vegetables are cleaned, cut into pieces of convenient size, mixed 

 with i to 3 per cent of salt and tightly packed in a fermentation vessel 

 of wood, earthenware or cement. A perforated cover is placed on top 

 and weighted down with stones. The vegetable juices are forced out by 

 the combined action of the salt and pressure and the solM matter reduced 

 in volume one-third or one-half. 



A gaseous fermentation commences within twenty-four hours if the 

 temperature is favorable, 18 to 20, and continues for several weeks. 

 At the end of this time the sugar in the juices has been destroyed and 

 acids, principally lactic, produced to the extent of .5 to i.o per cent. 

 The liquid is then drawn off and replaced with 4 to 8 per cent of brine 

 in which the vegetables will keep in good condition for a long time if 

 kept from the air. 



The fermentation is due to a large number of microorganisms origina- 

 ting on the surface of the vegetables and in the water. The yeasts attack 

 the sugar and exhaust the oxygen. The lactic bacteria at the same 

 time produce lactic acid. This is the principal fermentation and produces 

 the acidity to which the conservation of the mass is due. Many other 

 substances are formed by the complex fermentation, the principal pro- 



