FOODS AND CONDIMENTS 179 



WALTER OSTWALD and A. RIEDEL made a porous starch bread by 

 adding a starch paste to the starch dough before baking. A " pseudo- 

 coagulation" occurred during the baking, the unburst starch grains 

 abstracting water from the burst ones. The internal friction of the 

 paste becomes so great that the air bubbles cannot escape during 

 the baking process, the dough does not fall but is fixed as a foam. 



[In discussing the physical chemistry of bread making, E. J. COHN and L. J. 

 HENDERSON (Science, Nov. 22, 1918, p. 501, et seq.) conclude that "the acidity of 

 the dough, at the time of baking, seems to be the most important variable factor 

 in bread making." Soluble serum protein is an acceptable physical substitute 

 for gluten. Tr.] 



Beer. 



The fermentation industry so highly developed scientifically and 

 technically has already paid attention to colloid chemistry and pro- 

 duced a not inconsiderable literature (see F. EMSLANDER * 3 ) which 

 in part, however, is not altogether free from dilettantism. 



It would take us too far afield, were we to consider the whole 

 process of beer brewing l from the colloid-chemical viewpoint; we 

 must restrict ourselves to the finished product. 



Beer is a fermented beverage with an alcohol content of from 2 to 

 5 per cent, some acetic acid and from 4 to 8 per cent extractives. 



The extractives consist in greatest part of carbohydrates (maltose, 

 dextrin and gums), to a lesser extent of proteins (about 0.6 per cent), 

 and in addition, salts, hop bitters, hop resin and several alkaloidal 

 substances, besides small quantities of fermentation products such 

 as glycerin, lactic acid and succinic acid. 



The persistent fine foam which a fresh beer should show is brought 

 about by its colloidal content. It is a sign that the colloids have not 

 yet been broken down too far, and has at the same time the more 

 important purpose of retaining the carbonic acid gas. In a solution 

 supersaturated with gases, the formation of bubbles is either in- 

 creased or diminished by the colloids present at the moment. We 

 know further, from page 34, that a certain pressure is necessary to 

 overcome the surface tension and burst the bubble, e.g., a soap bubble, 

 so that the carbonic acid gas of beer is under a certain pressure 

 beneath the foam. 



The condition rather than the amount of the foam-forming albu- 

 mins is more important for the foam-keeping quality of beer. There 

 are beers rich in albumin which remain foamless and beers poor in 

 albumin which foam well. According to F. EMSLANDER* it is mainly 

 the soft hop resin, in addition to the acidity of the beer, which makes 

 the albumins foam. 



1 RICH. EMSLANDER calls attention to an interesting relation between beer 

 brewing and inactivation of ferments by shaking, see p. 189. Brewers have long 

 known that shaking by trains, machines, etc., interferes with the fermentation 

 and lagering of beer. 



