Extract 5 grams of the finely pulverized sample on a hardened filter
with five successive portions (10 cc. each) of ether, wash with small
portions of 95-percent alcohol by volume until a total of 200 cc. have
passed through, place the residue in a beaker with 50 cc. of water,
immerse the beaker in boiling water and stir constantly for 15 minutes
or until all the starch is gelatinized; cool to 55° C., add 20 cc. of
malt extract and maintain at this temperature for an hour. Heat again to
boiling for a few minutes, cool to 55° C., add 20 cc. of malt extract
and maintain at this temperature for an hour or until the residue
treated with iodin shows no blue color upon microscopic examination.
Cool, make up directly to 250 cc., and filter. Place 200 cc. of the
filtrate in a flask with 20 cc. of hydrochloric acid (sp. gr. 1.125);
connect with a reflux condenser and heat in a boiling water bath for 2.5
hours. Cool, nearly neutralize with sodium hydroxid solution, and make
up to 500 cc. Mix the solution well, pour through a dry filter and
determine the dextrose in an aliquot. Conduct a blank determination upon
the same volume of the malt extract as used upon the sample, and correct
the weight of reduced copper accordingly. The weight of the dextrose
obtained multiplied by 0.90 gives the weight of starch.