642 



MICROBIOLOGY OF ALCOHOLIC FERMENTATION 



the top of the cask. These holes should be covered with varnished 

 metal netting to prevent the entrance of flies. 



The top bung hole is then closed with a cork, through which a funnel 

 passes, furnished at its lower end with a glass tube extending to within 

 a few inches of the bottom of the cask. By means of this funnel 

 new liquid can be added without disturbing the surface film. The 

 lower bung-hole is closed with a cork, through which passes an 

 L-shaped glass tube which serves as an indicator of level and which 

 also can be used to draw off the vinegar. 



FIG. 159. Vinegar barrel. Z,, Surface of liquid; 0, O, openings for entrance of 

 air; t, tube for introducing new supplies of wine without disturbing surface films; 

 E, glass tube to show level of liquid and for drawing off vinegar. (Original.) 



When this apparatus is working well, from one-fifth to one-quarter 

 of the contents may be taken off every three or four weeks. This 

 depends on the temperature, which should be between 10 and 18. 

 The vinegar drawn off is immediately replaced with wine or cider which, 

 if added slowly, will, owing to its lower specific gravity, remain at the 

 surface in contact with the bacterial film. 



ORLEANS METHOD. This is practically the same as the method just 

 described with slight modifications to adapt it to large scale opera- 

 tions. It is the oldest commercial method and produces vinegar of the 

 highest quality. 



Barrels of about two hectoliters are usually employed, fitted 



