PROTEIDS 33 



sugar as possible is proflucod. At tliis point the plantlets 

 are killed by heat so that they will not use np arn^ of the 

 sugar they have made. The sweet substance is then dis- 

 solved out bj' soaking the malted grains in water. From the 

 liquid so .sweetened, lager beer and other malt liquors are 

 made by subsequent fermentation with yeast. Diastase 

 separated from malt may be used instead of an acid to con- 

 vert starch into sugar. 



30. Proteids. Let us I'cturn now to that other constituent 

 of the wheaten dough, the elastic material which remained 

 after removal of the .starch. This is known as gluten ' and 

 is a mixture of several substances which belong to the class 

 known as proteids.- To this class belong also the substances 

 which form the chief part of our own flesh and blood — and 

 indeed, mainly constitute the living substance of all plants 

 and animals. Hence, proteids must l)e regarded as the 

 most precious of all food substances. Like the carbohydrates 

 they contain carbon, hydrogen, and oxygen (though in some- 

 what different ]iroportions), but in addition they always 

 have a certain amount of nitrogen, and usually a little sulphur 

 and phosphorus. The nitrogenous nature of the proteids 

 is made evident by the pungent ammoniacal odor which 

 is given off when anj' of them are burned, — ammonia being 

 NH;,. Although in chemical composition proteids are all 

 very much alike, there are important differences in their 

 solubility — some, like white of egg, dissolving in cold water, 

 while others, such as those of the "wheat gum" are in- 

 soluble. Among the latter is a form of proteid called glutin 

 or gliadin which gives to wheat-gluten its wonderful tenacity 

 and elasticity. 



It is a significant fact that wheat is the only one of the 

 cereals which contains gliadin in any considerable amount, 

 although it should be said that rye contains a closely similar 

 proteid. Macaroni, which owes its consistency chiefiy to 

 gliadin, is therefore made only from wheat: and wheaten 

 dough alone possesses just the right tenacity and elasticity 

 for making the lightest, spongiest loaf. The lightest rye bread 



1 Glu'ten < Ij. glutiis, tenacious. 

 - Pro'te-id < Gr. protos, before. 



