272 FOOD AND FOOD ADULTERANTS. 



After the mashing process comes the boiling of the wort, which is be- 

 gun as soon as it is drawn off from the exhausted malt and continued 

 for one to two hours. This prevents the formation of acid, and serves 

 to extract the hops, which are added at this stage of the process. The 

 boiling of the wort with hops serves not only to impart to it the de- 

 sired hop flavor, but also to partially clarify it by precipitating some 

 albuminous matter by means of the tannin in the hops, and to en- 

 hance its keeping qualities. To this end larger quantities of hops are 

 used for beers intended for exportation or long keeping. 



The wort is now ready to be submitted to the most important oper- 

 ation of all fermentation which calls for very careful supervision on 

 the part of the brewer. 



FERMENTATION, 



After the wort has been boiled with hops it is cooled as rapidly as 

 possible, to prevent the formation of acid, usually effected by means of 

 artificial refrigerating apparatus ; it is then ready for the addition of the 

 yeast. 



There are two distinct methods of fermentation in use, called by the 

 Germans Ober- und Untergahmnff t aad by the French fermentation haute 

 (top fermentation) and basse (bottom fermentation). The former is 

 carried on at a comparatively high temperature, the action is rapid, and 

 the yeast with the impurities is carried to the surface of the liquid ; in 

 the latter method the temperature is kept low, the fermentation goes 

 on slowly, and the yeast and impurities sink to the bottom. The sec- 

 ond method is often called the Bavarian method, as it seems to have 

 originated there, and is used exclusively in that country. It is gener- 

 ally preferred in Germany and France, while in England and this 

 country the upward clearing method appears to be more in vogue. 



The nature of the fermentation depends greatly upon the character 

 of the yeast used, for Pasteur's experiments have shown that yeast from 

 upward-fermented beer tends to produce the upward fermentation, 

 while yeast from bottom-fermented beer produces the bottom fermenta- 

 tion. The purity of the yeast used is of the very first importance in 

 the production of good beer. Many experiments have been made with 

 the end in view of producing a perfectly pure yeast, which should con- 

 tain only the yeast ferment proper, and thus produce a beer of good 

 flavor and keeping properties, free from diseased or acid ferments. 



PURE YEAST. 



The production of pure yeast for brewing purposes has been put on 

 a practical basis of late years through the scientific researches of Dr. 

 E. C. Hanseii, of the Carlsberg Institute, in Copenhagen. I Fe succeeded 

 in producing a pure yeast cultivated from a single c< II. lie was able to 

 differentiate- in this way six different species or varieties of sacckaromy- 

 cetes, several of which may usually be, found in an ordinary brewer^ 



