AOAC Official Method 935.24 Starch (Unconverted) in Beer Iodine Reaction Method
Procedure
(a) For light beer.—Fill 15 mm diameter test tube to within 2.5 cm from rim with beer, 920.49 (see 27.1.01). Carefully add 0.02M I2 from dropper to form distinct layer on top of beer. Observe at once, by transmitted light, color developed at interface. Report blue as indicating presence of starch; purple, amylodextrin; and reddish tinge, erythrodextrin. Qualify results by using terms faint trace, trace, and plain trace according to whether the color developed is faint, distinct, or strong.
(b) For dark beer, but applicable also to a light beer.—To 5 mL beer in test tube add 25 mL alcohol, shake thorougly, and let stand. Decant, pouring off last trace of beer-alcohol mixture Dissolve precipitate (dextrin) in 5mLH2Oand to this solution add 0.02M I2 solution dropwise. Interpret as in (a).
