STBtrCTURE OP THE HOP CONE. 285 



Behrens holds that no great importance attaches to tannic 

 acid in this connection, but that the colour is greatly 

 influenced thereby, the larger the quantity of hop tan- 

 nin present the paler the beer. 



Nitrogenous constituents} — The total nitrogen in hops 

 amounts to 2 to 4 per cent. It is believed that the soluble 

 nitrogenous materials in hops stimulate the yeast in strongly 

 hopped beers to increased assimilation of nitrogen (Hay- 

 duck). Bungener detected asparagin in hops ; and Griess 

 and Harrow found cholin in aqueous hop extract acidified 

 with hydrochloric acid. Griessmayer, however, believes 

 that cholin does not exist ready formed in hops, but that 

 it is a constituent of the lecithin they contain. 



Acidity or acid content of hops.^- — ^A freshly prepared aqueous 

 hop extract has a more or less acid reaction. Behrens in- 

 clines to the view that the increased acidity of wort subse- 

 quent to hopping is due to the acids introduced into the hops, 

 without this increased acidity having any appreciable import- 

 ance so far as the sterilisation of the wort is concerned. 



Calculated in terms of lactic abid, the acidity of hops 

 varies, according to the variety and the season, from 2'81 

 to 6'75 per cent. (Behrens) of the air-dry matter. Behrens 

 assumes that the degree of acidity has an important bearing 

 on the colour of hops, since the dreaded red or brown col- 

 oration only appears when they are deficient in acidity, 

 through loss or neutralisation of acid by lixiviation, or the 

 action of light or of mould fungi. Fresh, healthy hops 

 owe their acidity to phosphoric acid, malic acid and citric 

 acid, either in the free state, or, what is more probable, in 

 combination as acid salts. 



^E. Prior, Chemie und Physiologie des Maizes und des Bieres, Leipzig, 

 1896. 



2 Behrens, Studien iiber die Conservirung mid Zusammensetzung des. 

 Hopfens, Berlin, 1896. 



