AOAC Official Method 941.16 Filth in Grain Products and Brewer’s Grits

(Applicable to corn grits, rye and wheat meal, whole wheat flour, farina, semolina.)
A. Rodent Excreta
Weigh 50 g test portion sample in 250mLhooked-lip beaker. Add CHCl3 to within ca 1 cm of top, mix thoroughly, and let settle 30 min,stirring surface layer occasionally. Carefully decant CHCl3 and float tissue onto Büchner, without disturbing heavy residue in bottom of beaker. Before decanting, take care that floating layer has not become so compact as to render this operation difficult. Add amount of CCl4 equal to amount of CHCl3 and tissue left in beaker, let settle again, and decant as before. Repeat this process with mixture of equal parts CHCl3 and CCl4 until very little tissue remains in beaker. Do not decant any rodent excreta fragments that may be present. Wash residue in beaker onto 7 cm ruled paper with stream of CHCl3 or CCl4 and examine microscopically. Retain decanted floating tissues for light filth analysis.

Reference: Cereal Chem. 18, 655(1941).

B. Light Filth
(Not applicable to whole and degerminated corn meal.)
Draw air through material in Büchner, A, until liquid evaporates. Air dry overnight, or dry in oven at ca 80°C. (Caution: In oven drying,phosgene is liberated and adequate ventilation must be provided.) Transfer residue to 1 L trap flask, 945.75B(h)(4) (see 16.1.01). Add 100 mL 60% isopropanol saturated with heptane, 945.75C(n) (see 16.1.01), and mix thoroughly. Wash down sides of flask with isopropanol-heptane solution until ca 400 mL is added, and soak 30 min. Trap off twice with 20–30 mL heptane, 945.75C(l) (see 16.1.01), for each trapping and 60% isopropanol saturated with
heptane as liquid extraction medium. In first trapping, let stand 5 min after stirring in heptane before filling flask. Filter, and examine both trappings microscopically.

Revised: March 1997