538 SCIENCE PROGRESS 



Colour 



It is of interest at the present juncture to discuss this ques- 

 tion of colour more in detail. As a matter of fact the colour 

 of a loaf is largely a question of optics and depends even more 

 on the character of the flour used than on its whiteness. It is 

 agreed that perfection of colour implies brightness of appearance 

 in both crumb and crust and it is found that a weak flour, 

 though very white in colour, makes loaves of poor, dingy 

 appearance. Questions of the refraction and reflection of light 

 enter far more into the colour of the loaf than is supposed. 



It is well known to the baker that the better aeration of a 

 loaf produced by the admixture of a stronger and possibly 

 darker-coloured flour with an originally weak flour causes a 

 distinct increase in the apparent whiteness of the bread. 



The invention of the roller mill and the vast improvement 

 in the technique of milling, which has been so marked in the 

 last few decades, has involved the almost entire elimination of 

 fragments of dirt and husk from flour : for this reason bread 

 has tended to become whiter than formerly, though the 

 nutritive qualities have been in no way impaired. 



There is of course no relation between the colour of bread 

 and its nutritive value and the standard of colour is from this 

 point of view a false one. 



The fetish of colour-worship being established, means were 

 sought by the trade of improving the colour of flours which 

 lacked whiteness and were principally for that reason classed 

 as lower grade, again without any reference to their nutritive 

 value. The spurious addition of alum — originally added so as 

 to make it possible for the baker to deal with flour milled 

 from wheat which had begun to germinate — which has the 

 effect of making the bread look very white, is happily a thing 

 of the past in this country. 



A modern development, however, is the application of 

 methods of bleaching flour artificially in milling practice. Most 

 of these methods involve the agitation of the flour, during a 

 few seconds only, with an atmosphere containing very small 

 quantities of the oxides of nitrogen or ozone, whereby a process 

 of nitration or oxidation or both of the colouring matter takes 

 place and the flour is bleached more or less according to the 

 time of exposure. Opinions of scientific men are divided as to 



