108 Mr. Roberts on the Action of Isinglass 



Suppose, for example, that sixteen fluid ounces of the 

 acid porter to be tried, is put into a vessel that will contain 

 about double that quantity. 



Carefully measure a given portion of the standard liquor, 

 say four fluid ounces. Add small quantities of this standard 

 liquor to the acid porter (stirring the mixture upon every 

 addition), until the effervescence ceases, or until the mixture 

 is so neutralized by the standard liquor, as not to change 

 the colour of litmus paper when it is dipped in. The mix- 

 ture may further be tried by turmeric paper, which should 

 be changed to a higher colour by the mixture, thereby 

 showing that the alkali of the standard liquor is slightly in 

 excess. — By the quantity of standard liquor required to 

 produce this result, may be known the greater or less 

 degree of acidity of the porter to be used for making 

 clearings. 



Sixteen fluid ounces of acid porter, such as is used by one 

 of the largest breweries in Ireland for making clearings, 

 standing 1° Twaddle's hydrometer, 61° F. temperature, re- 

 quired four fluid ounces of standard liquor to neutralize it, 

 which is equal to 1 part bi-carbonate of potash to 64 parts 

 of acid porter. 



This appears a good average strength of acidity for por- 

 ter, when required for making clearings. If acid porter 

 required less standard liquor to neutralize it than the above 

 quantity, it would indicate a weakness of acidity, which 

 would render such porter an imperfect solvent for Isinglass. 



Acid porter, such as the above trial was made with, acts 

 upon Isinglass, at 61° F., but its action is much facilitated 

 by an increase of temperature of 80° or 90° F. 



During the fermentation of malt liquor, the saccharine 

 matter of the malt is gradually converted into alcohol, by 

 the agency of yeast and atmospheric air ; ultimately the 

 liquor passesfrom the vinous into the acetous fermentation. 



This latter state is prevented by the exclusion of atmo- 

 spheric air ; hence, the necessity of bunging securely malt 

 liquor, when the vinous fermentation is complete, other- 

 wise the liquor will become sour. 



It is when unfined porter is put into casks, and the 

 vinous fermentation has, either in part or entirely, ceased, 

 that brewers apply the clearings to the best advantage. The 

 manner in which Isinglass acts upon unfined liquor in clear- 



