UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 839 
Contribution from the Bureau of Chemistry 
CARL L. ALSBERG, Chief 
yu^"^ 
Washington, D. C. 
April 23, 1920 
MICROSCOPICAL EXAMINATION OF FLOUR. 
By George L. Keenan, Microanalyst, and Mary A. Lyons, Microanalyst , 
Microchemical Laboratory. 
CONTENTS. 
Page. 
Review of literature 1 
Purpose of investigation 3 
Microscopical method 3 
Sources of variation in method 5 
Examination of mill stocks 11 
E xamination of commercial grades of flour . . 
Examination of experimental series of flour. 
Summary 
Bibliography 
Page. 
16 
29 
31 
32 
REVIEW OF LITERATURE. 
A review of the literature has shown very few methods for the 
microscopical examination of flours. In the great majority of the 
methods found, suggestions are offered for the separation of the 
wheat tissues from the starch material and the subsequent examina- 
tion of the offal under the microscope. The results obtained from 
such microscopical examination, however, are only roughly indicative 
of the offal that may be present. 
The work of Delaye (5) 1 was concerned largely with the detection 
of foreign spores in flour and also with the presence of ergot. Girard 
(7) suggested the separation of the gluten from the starch and im- 
purities by forming the flour into a cake and washing it with running 
water. The starch and impurities were separated with a fine sieve, 
and the offal particles examined under the microscope. Kraemer 
(11) has offered a quantitative method for the examination of com- 
mercial flours by means of the microscope, this quantitative method 
to be preceded by a general qualitative examination. A small por- 
tion of the flour was weighed out, a few drops of a reagent added, 
and the number of typical starch grains or characteristic tissues 
enumerated in examining five different portions of the microscop- 
ical mount. Standard samples were employed for purposes of com- 
1 The numbers in parenthesis refer to the bibliography on page 32. 
152332°— 20— Bull. 839 1 
