• The Composition and Food Valve of Bread. 21 



into the oven, and the greater the expansion as the temperature 

 rises during the process of baking. 



The epithet well piled perhaps requires some explanation. 

 A well piled loaf is one in which both the shape and the 

 texture are good. Good shape and texture depend on the 

 qualitj' of the gluten, and this in turn depends on the soluble 

 salts contained in the flour. Gluten is a colloid substance, and 

 like all colloids its properties varj- with its surroundings. This 

 is well shown in the familiar case of albumen or Avhite of egg. 

 In its natural condition it is a thick glairy liquid. On heating 

 it coagulates and changes its properties, becoming a white, soft 

 solid. A somewhat similar change in propei'ties is brought 

 about by the presence of acid, or of certain salts. Another 

 instance of a colloid substance is the clay of the soil. The 

 extent to which the properties of such a soil can be modified 

 by the application of lime or other manurial substances, both 

 for better or worse, is a matter of common knowledge. The 

 soluble salts present in different wheats vary greatly both in 

 kind and' in degree. Certain wheats, notably the hard wheats 

 of Canada, are specially rich in soluble phosphates, and contain 

 comparatively small proportions of sulphates and chlorides. 

 Other wheats, and amongst them especially Rivet, and many of 

 the heavy cropping wheats commonly grown in England, 

 contain but little soluble phosphate and much svilphate and 

 chloride. Now sulphates and chlorides have the power of 

 making gluten short aiid crumbly, whilst phosphates make it 

 tough and elastic. Hence the gluten of Canadian hard wheats 

 is tougher and more elastic than the gluten of home-grown 

 wheats, and toughness and elasticity are the precise qualities 

 necessary to hold the loaf in a good and symmetrical shape as 

 it expands when heated in the oven, and to ensure a good 

 texture by preventing the small vesicles of gas in the dough 

 from breaking into one another and forming large holes. 



The bearing of these properties on the feeding value of 

 bread is perhaps indirect. Nevertheless, it cannot be neglected. 

 High diastatic power which produces a large loaf is very 

 generally associated with a high percentage of protein. The 

 power of baking a well piled sha})ely loaf is associated with a 

 high percentage of solul)Ie phosphate, and other things being 

 equal, with a high percentage of gluten, the chief protein of 

 the wheat grain. A strong flour possessing both these proper- 

 ties is therefore usually above the average in content both of 

 protein and of phosphate, and the undoubted preference shown 

 by the working man for white bread made from strong floui- 

 is, so far, well founded, for strong flour gives him on the 

 average more nitrogen and more phosphate, the two consti- 

 tuents in which his dietary is most likely to be lacking. At 



