124 THE CARBOHYDRATES 



sweet taste owing to the conversion of starch into maltose ; if 

 the latter substance be estimated from time to time, it will be 

 found that the reducing power of the mixture increases rapidly 

 at first until, after about two hours, the amount of maltose 

 present corresponds to about 80 per cent of the starch em- 

 ployed, when practically no further change takes place. The 

 change in the starch paste can also be demonstrated by peri- 

 odic testing with iodine solution ; the blue-black coloration 

 gradually becomes less and less marked until various shades 

 of red are obtained, finally the iodine gives no distinctive 

 coloration. A corresponding fall in the optical activity of the 

 solution can also be observed, but as the activity is still greater 

 than what it should be for maltose alone, it must be concluded 

 that some other substance is formed at the same time as the 

 maltose, and that its reducing power is less but its activity is 

 greater than that of maltose. The amount of this " non-maltose " 

 product of diastatic activity varies directly with the tempera- 

 ture, and increases considerably at the expense of the maltose 

 if the temperature be kept at or above 60 ; if to such a pro- 

 duct, rich in non-maltose, a fresh quantity of malt extract be 

 added, the non-maltose will be attacked and converted into 

 maltose until the amount present again attains the value 80 

 per cent, which is the normal maximum ; this experiment, 

 which is due to Brown and Morris,* shows that the non-maltose 

 is composed of different constituents, some of which are con- 

 verted into maltose by diastase more readily than others ; 

 moreover experiments have shown that these substances behave 

 differently towards yeast, some being more readily fermentable 

 than others. This non-maltose constituent represents a mix- 

 ture of the various dextrins mentioned above as having been 

 described by several authors. More recently Maquenne and 

 Roux f and others, carrying on the experiments of Brown and 

 his collaborators, have found that on prolonged action extend- 

 ing over several days, even this non-maltose is slowly attacked 

 by diastase, and a practically theoretical yield, instead of only 

 an 80 per cent yield, can be obtained. 



The action of malt on starch accordingly takes place in two 

 stages, of which the first is rapid, being completed in about 



* Brown and Morris: " J. Chem. Soc., Lond.," 1885, 47, 527. 

 f Maquenne and Roux : " Compt. rend.," 1906, 142, 124, 1059. 



