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ments obtained by certain brewers, who, thanks to the ex- 

 perience of years, knew how to choose yeast which gave a 

 particular taste, and also how to employ preventive measures 

 against accidental and pernicious ferments (such as the use of 

 ice, or of hops in a larger quantity). But, though laughing 

 at Bertin's jokes, Pasteur was convinced that great progress in 

 the brewer's art would date from his studies. 



He was now going through a series of experiments, buying 

 at Bertin's much praised cafe's samples of various famous beers 

 Strasburg, Nancy, Vienna, Burton's, etc. After letting the 

 samples rest for fwenty-four hours he decanted them and 

 sowed one drop of the deposit in vessels full of pure wort, 

 which he placed in a temperature of 20 C. After fifteen or 

 eighteen days he studied and tasted the yeasts formed in the 

 wort, and found them all to contain ferments of diseases. He 

 sowed some pure yeast in some other vessels, with the same 

 precautions, and all the beers of this series remained pure from 

 strange ferments and free from bad taste ; they had merely 

 become flat. 



He was eagerly seeking the means of judging how his labora- 

 tory tests would work in practice. He spent some time at 

 Tantonville, in Lorraine, visiting an immense brewery, of 

 which the owners were the brothers Tourtel. Though very 

 carefully kept, the brewery was yet not quite clean enough to 

 satisfy him. It is true that he was more than difficult to 

 please in that respect; a small detail of his everyday life 

 revealed this constant preoccupation. He never used a plate 

 or a glass without examining them minutely and wiping them 

 carefully; no microscopic speck of dust escaped his short- 

 sighted eyes. Whether at home or with strangers he in- 

 variably went through this preliminary exercise, in spite of 

 the anxious astonishment of his hostess, who usually feared 

 that some negligence had occurred, until Pasteur, noticing her 

 slight dismay, assured her that this was but an inveterate 

 scientist's habit. If he carried such minute care into daily 

 life, we can imagine how strict was his examination of scien- 

 tific things and of brewery tanks. 



After those studies at Tantonville with his curator, M. 

 Grenet, Pasteur laid down three great principles 



1. Every alteration either of the wort or of the beer itself 

 depends on the development of micro-organisms which are 

 ferments of diseases. 



