68 MICRO-ORGANISMS IN WATER 



{Hansen). — In the case of water used for brewing pur- 

 poses, the mere numerical determination of the bacterial 

 contents is of little moment, whilst it is of great import- 

 ance to ascertain whether bacteria are present which 

 will develop in the malt extract or beer, and so possibly 

 exercise a deleterious effect upon the liquor. Eecog- 

 nising this fact, Hansen^ uses, instead of gelatine- 

 peptone, sterilised wort and sterilised beer respectively 

 as culture media. 



By thus abandoning solid culture media for these 

 liquid ones, Hansen has to adopt of course a totally 

 different method of forming an approximate estimate of 

 the number of microbes in the water under examination. 

 The method he employs is in fact a modification of 

 Miquel's (see p. 7o), which we shall subsequently de- 

 scribe, but it will be convenient to indicate Hansen's 

 precise mode of procedure with regard to brewing- 

 waters at this stage. 



Hansen takes 15 small flasks containing sterile malt- 

 wort and 15 similar flasks with sterile beer, and to each 

 of these he adds 1 drop (of known volume) of the water 

 under examination, whilst to each of 10 further flasks 

 of sterile wort and 10 of sterile beer respectively he 

 adds ^ c.c. of the same water. The 50 flasks to which 

 the water has thus been added are kept at 25° C, and 

 examined after 14 days to see how many of them have 

 become turbid through growths. From the percentage 

 number of turbid flasks an opinion can be formed as 

 to the bacteriological fitness of the water for brewing, 

 whilst an estimate of the number of micro-organisms 

 capable of flourishing in these media can be arrived at 

 in the following manner. Thus, taking the 10 flasks of 



^ * Methode zm Analyse des Brauwassers in Riicksicht auf Mikro- 

 organismen,' Zeitschrift fur das ges. Brautvesen, 1888, No. 1. Also 

 TJntersuchit/ngen aus der Praxis der Gdrungsindustrie^ Mtinchen und 

 Leipzig, 1892, p. 1. 



