EXPERIMENTAL MILLING AND BAKING. 
31 
is increased as well as the activities of the yeast. The optimum 
reaction corresponds to a P H of approximately -5.0. For choice flours 
this figure is a little higher, and for the poorer grades a little lower. 
The percentage acidity of flour ordinarily diminishes with in- 
creasing refinement and grade. Exceptions to this rule are found, 
Fig. 24— Kjeldahl distilling apparatus with glassware in position for making test. Supply of caustic 
soda and automatic pipette to left of the still. 
however, in flour made from unsound wheat, or in flour milled from 
wheat containing noticeable quantities of inseparable foreign mate- 
rial. It is necessary that a normal acid limit for each grade of flour 
in sound condition be established before its acidity value can be used 
to judge its condition. As a rule, sound flours are low in acidity, 
whereas flours which have spoiled or are made from spoiled wheat 
