1 86 SCIENCE PROGRESS 



can more readily obtain their food from wheaten flour ; partly 

 because high-class bread is darkened by them ; partly because 

 they contain so much natural moisture that their use is not 

 profitable ; partly because much more effective and reliable 

 yeast foods have been invented or adopted. Where some form 

 of "yeast food" is wanted, most bakers nowadays use either 

 sugar itself or malt extract. I need not now pause to inquire 

 whether yeast can get its food directly from cane-sugar or 

 whether the hydrolising constituent of yeast has first of all to 

 change cane-sugar into some other form of sugar before yeast 

 can utilise it ; but in effect we have in sugar a food which 

 yeast can assimilate, and in malt extract an article which by 

 diastatic action can convert starch into a food for yeast. 

 Only an exceedingly small quantity of either is required — less 

 than i per cent, of sugar and say 0-25 per cent, of malt extract, 

 taking the quantity of flour used as the basis of calculation. 

 " Malt diastase " or " absolute diastase " can bring about the 

 same result, and then the infinitesimal proportion of o"02 per 

 cent, will bring about striking differences in the size, appearance, 

 and flavour of loaves produced from some flours. 



Nobody could, or at any rate would, as an article of ordinary 

 diet, eat loaves of the usual shape made from a mixture of flour, 

 salt, and water, and baked soon after the mixture is made. 

 Such a "loaf" made of 2 lb. 2 oz. of dough and baked in a tin 

 would measure say 1,000 c.c. The same ingredients properly 

 fermented and baked in a tin would measure say 2,800 c.c. The 

 difference is due to inflation by gas, mostly carbon dioxide. 

 In the first case, the crust would be so hard that ordinary 

 human teeth could not break it, yet the " crumb " would be 

 practically dough itself, utterly repugnant to the taste, and 

 highly indigestible. Unless such a dough be baked in very thin 

 layers, which the heat could penetrate in baking, it is inedible, 

 and in that form it is no longer bread as modern people 

 understand the term. Aeration is essential. This may be 

 brought about in several ways. 



If a mixture of flour, salt, and water be put into a sterilised 

 receptacle, covered up and left under favourable conditions for 

 say thirty hours, one or more forms of fermentation are set up 

 spontaneously. I need not attempt to say what chemical changes 

 have taken place, or what gases have been generated, but the 

 loaves so produced, bad though they may be, are very much 



