496 THE LIFE-WORK OF A CHEMIST. 



In September, 1871, Pasteur visited one of the large London brew- 

 eries, in which the use of tlie microscope was then unknown. A single 

 glance at the condition of the yeast instantly told its tale, and enabled 

 him to explain to the brewers the cause of the serious state of things 

 by which frequently as much as 20 per cent, of their product was 

 returned on their hands as unsalable — this being that this yeast con- 

 tained forsigD or unhealthy organisms. And just as pure yeast is the 

 cause of the necessary conversion of wort into beer, so these strange 

 forms which differ raor[)hologically from yeast, and whose presence can 

 therefore be distinctly ascertained, are the cause of acidity, ropiness, 

 turbidity, and other diseases which render the beer undrinkable. It is 

 no exaggeration to say that, whereas before Pasteur's researches the 

 microscoi)e was practically unknown in the brew-house, it has now be 

 come as common as the thermometer or the saccharimeter, and by its- 

 help and by the interpretations we can i)lace upon its revelations through 

 Pasteur's teaching, yeast — of all brewers' materials the least open to 

 rough and ready practical discernment — becomes easy of valuation as 

 to its purity or impurity, its vigor or weakness, and therefore its 

 behavior during fermentation. Thus, while in former days the most 

 costly materials were ever liable to be ruined by disease organisms 

 unconsciously introduced into them with the yeast, at the present day 

 the possibilities of any such vast pecuniary disasters become easil}" 

 avertable. 



Of all industries, brewing is perhaps the one which demands the most 

 stringent care in regard to complete and absolute cleanliness. The 

 brewers' materials, products, and by-products, are so putrescible, there 

 is always so vast an abundance of disease organisms in the brewery air, 

 that the minutest amounts of these waste products lying about in ves- 

 sels or pipes transform these places into perfect nests for the propa- 

 gation of these microorganisms, whence, transferred into the brewings, 

 they inevitably ruin them, however carefully and scientifically prepared 

 in other respects. Without the microscope, any breach of discipline in 

 the way of the supreme cleanliness necessary is impossible of detection ; 

 with it we can track down the micro-organisms to their source, whether 



V 



it be in uncleanly plant, in impurity of materials, or in carelessness of 

 mani[)ulation. 



Among the more direct applications of Pasteur's researches, the so- 

 called Pasteurization of beer claims a place. Pasteur showed that tem- 

 peratures well below the boiling-point sufficed for destroying the disease 

 organisms in alcoholic fluids, and, based on these results, enormous 

 quantities of low-fermentation beers are annually submitted to these 

 temperatures, and thus escape the changes otherwise incident to tue 

 micro organisms which have succumbed to the treatment. This process 

 is however for several intricate reasons, not suited for English beers, 

 but if we can not keep our beers by submitting them to high tempera- 

 tures, we can foretell to a nicety how they will keep by artificially forc^ 



