UNITED STATES DEPARTMENT OF AGRICULTURE 



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BULLETIN No. 839 



Contribution from the Bureau of Chemistry 

 CARL L. ALSBERG, Chief 



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Washington, D. C. 



April 23, 1920 



MICROSCOPICAL EXAMINATION OF FLOUR. 



By George L. Keenan, Microanalyst, and Mary A. Lyons, Microanalyst , 

 Microchemical Laboratory. 



CONTENTS. 



Review of literature 1 



Purpose of investigation 3 



Microscopical method 3 



Sources of variation in method 5 



Examination of mill stocks 11 



Examination of commercial grades of flour ... 16 



Examination of experimental series of flour. 29 



Summary 31 



Bibliography 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. 

 -20— Bull. 839 1 



