FERMENTATION 353 



specific gravity of the solution of the whole amount of starch-sugar, as found in the 

 table, represented the original gravity of the beer. 



' This method must give an original gravity slightly higher than the truth, owing 

 to the circumstance that the dextrin, albumen, and salts, which are found among the 

 solid matters dissolved in beer, are treated as having the low gravity of extractive 

 matter, and accordingly amplified by about one-sixth, like that substance, in allowing 

 for them ultimately as starch-sugar. The error from this source, however, is incon- 

 siderable. It is to be further observed, that the error from imperfect manipulation, 

 of which there is most risk in the process, is leaving a little sugar in the extractive 

 matter from incomplete fermentation. This accident also increases the original 

 gravity deduced. The process has given results which are remarkably uniform, and 

 is valuable in the scientific investigation of the subject, although not of that ready and 

 easy execution which is necessary for ordinary practice, and which recommends the 

 former method.' 



The following is a statement by M. L. Pasteur of a new process for making beer so 

 as to render it unchangeable : 



' Every one knows that beer is very liable to change ; during the summer it will 

 deteriorate in a month or six weeks. 



' The wort used in the preparation of beer is very difficult to preserve. At a high tem- 

 perature the wort of beer, in the course of a few hours, especially in stormy weather, 

 will go through a great many different alterations. The alterations in the wort of beer 

 have such an influence in the making of this drink, that it becomes absolutely necessary 

 for the brewer to use the greatest precautions to guard against its disastrous effects. A 

 low temperature is essential to the preservation of the wort of beer, and sometimes ice 

 is employed. What, then, are these alterations which rule over the process of fer- 

 mentation, and why should not means for combating them be found, more simple 

 and more economical than those already in use ? I have devised a new process of 

 cooling and of fermentation, and the following are some of the results of my 

 work : 



' 1. The changes in beer are due to the development and the multiplication of 

 microscopical organisms which I will call sick fermentation. 



' 2. The germs of this fermentation are carried by the air, and by the utensils in 

 use, &c. 



' 3. Whenever the beer does not contain these living germs, which are the cause of 

 its deterioration, it becomes unchangeable, at whatever temperature it is made. 



' 4. I can show that by the employment of certain processes in brewing, all the 

 malt, all the yeast, and all the beer receive the germs of diseases proper to these sub- 

 stances. 



' Let us take a beer that has been made according to the usual process employed in 

 England, France, or Germany. Let us expose it in closed bottles at a temperature of 

 from 15 to 25 C. It constantly happens that this beer in the course of a few weeks 

 will be unfit for use. Its preservation is only possible, in some exceptional cases, by 

 the addition of a quantity of hops superior to those generally used. At the time that 

 the change is taking place, the microscopical organisms will make thIKr appearance 

 and multiply. What gives birth to these organisms ? 



' My studies have proved that the most changeable organic liquids, such as blood, 

 the juice of the grape, &c., can be preserved indefinitely, without any change what- 

 ever, when exposed to the ordinary air, but air deprived of those particles of dust 

 which it always carries about, and which are deposited on the surface of all the objects 

 of nature. The contradiction that this proposition has raised will soon be overcome 

 by a simple experiment which I have often shown before the Academy, and which 

 consists in shutting up the liquids in vessels, having an opening placed at the end of 

 a winding-tube, but so far removed from the liquid contained in the vessels that the 

 particles of dust held in suspension in the air cannot come in contact with the 

 liquid. 



' That settled, let us prepare a series of vessels where the wort of beer may be per- 

 fectly preserved for weeks, months, or years ; then, by a very simple process, which is 

 the employment of a second tube like that of which I have spoken, let us introduce 

 separately in each of these a drop from all the beers of commerce. As the clearest 

 beer always contains some globules of yeast in suspension, the alcoholic fermentation 

 will be established, and the wort of beer contained in each of them will in a few days 

 undergo some transformation. Or, if the experiment be carried on in a stove at 

 summer heat, and allowed to remain some weeks, the globules of ordinary alcoholic 

 yeast will soon be associated, in numbers more or less considerable, with the sick fer- 

 mentation of which I have before spoken. The germs of this fermentation exist in 

 all the beers of commerce. This interpretation of facts is confirmed by the following 

 results : 



VOL. H. A A 



