AIR AND WATER. 73 



Based upon these observations, Hansen devised the 

 following method : Small quantities of the water, either in 

 its original state or diluted, are added to a series of Freudenreich 

 flasks containing either sterilised wort or beer.* After in- 

 cubation at 25 C. for fourteen days the contents of the culture 

 flasks are submitted to examination. If only a part of them 

 show any growth, the rest remaining sterile, it may be assumed 

 with approximate certainty that each of the flasks belonging 

 to the former set has received only a single germ. Information 

 is thus gained concerning the number of germs capable of 

 development existing in an ascertained volume, and the 

 different germs are also under more favourable conditions 

 for their free development. An exact examination will then 

 show to what species these germs belong. 



Although wort - cultures give a very small number of 

 growths in this method in comparison with plate-cultures, 

 yet in many cases the number of wort-growths will still be too 

 high, for these growths are able to develop in the flasks un- 

 disturbed and without hindrance from other organisms, but 

 when wort is mixed with good culture-yeast in the fermenting 

 vessel, many of these germs will be checked. Further, the 

 flasks which show a formation of mould will have no import- 

 ance for the brewery itself, but only for the malt-house. In 

 order that the conclusions based on the results should approxi- 

 mate more closely to practical requirements, Hansen proposes 

 the following method of procedure : The flasks containing a 

 development of yeasts and bacteria are divided into two groups 

 (1) those in which the growths appear rapidly, and (2) the 

 remainder, in which they make their appearance later ; for 

 instance, after five days. Among the latter are those species 

 which develop less readily in wort. To these, then, less 

 importance is attached in forming an opinion as to the nature 

 of the water or air. 



The same principle is used by Wichmann, who endeavoured 

 to give a numerical expression for the " harmfulness " of 

 water that is to say, to express to a definite degree the 

 destructive property of water with regard to wort and beer. 



* In the analyses of air the germs are aspirated into sterilised water, or first 

 into cotton-wool and then transferred to water. 



