Scientific Lectures. 117 



peniiitted to dry down, it leaves a hard, transparent, glassy substance, 

 wliich requires considerable time to again dissolve in water. Now, 

 this is true, whether the change occurs Avithin the loaf or without. 

 T^e see at once the necessity of heating the loaf, in the process of 

 baking, to a temperature of 212 deg. throughout. The starch sacs 

 must be burst, and the starch granules moistened and resolved into 

 mucilage, to render the bread palatable. The heat must penetrate 

 throughout the loaf to expand the gas bubbles, and thus increase the 

 lightness of the bread, and, finally, it is essential to arrest and destroy 

 the ferment. But what does the heat do to the outside of the loaf? 

 It dehydrates and stiffens the gluten, of course. But it does more. 

 It roasts the gluten and starch at and near the surface, giving rise to • 

 grateful aromas and a beautiful reddish tint, if not carried too far. 

 The starch becomes dextrine, or British gum, and the loaf is arched 

 over to prevent the collapsing of the loaf, which heat and the last 

 eftects of fermentation have expanded to its full capacity. Some 

 chemists have ascribed the delicate red tint, which carefully regulated 

 heat will produce on bread and pastry, to assamar, a body discovered 

 by Reichenbach. I once obtained a liquid of an exquisite rosanaline 

 color, by heating, to the temperature of destructive distillation, a mix- 

 ture of dried flour with soda lime. It is probable that this body, 

 whatever it may be, is present in the crust of bread. 



Dextkine oe Gum in the Ceust. 



You all know, or, at least, all who have ever had anything to do 

 with the baking of bread, how hazardous it is to leave a loaf in the 

 baking tin after it is taken from the oven. It should be instantly 

 removed, as 3'ou are aware, siiice if this is neglected, the surface of 

 the loaf becomes moist and adhesive. This is due to the formation 

 of roasted starch or British gum in the crust. At the conclusion of 

 the baking process the loaf is exhaling steam. If it remains in the 

 pan, as the latter cools, the steam condenses to water at the surface of 

 tlie loaf, and liquifies the roasted starch, converting it into mucilage. 

 The adhesive nature of this substance, which makes it so useful in 

 the arts, was discovered, it is said, by accident, A flouring mill 

 somewhere in England burned down, and quantities of wheat were 

 roasted. It was noticed that the water that drained away from one 

 of the piles of roasted wheat was sticky. When the British govern- 

 ment instituted the penny post and the use of letter-stamps, the post- 

 ofiice department used this mucilage to secure the adhesion of the 



