A method for fractionating a milled grain product into coarse and fine fractions includes providing a sieving apparatus with a bottom chamber divided from a top chamber by a sieve, an inlet port in the top chamber, a top chamber cover defined by a plurality of openings, and a first exit port in the bottom chamber, and applying vacuum suction to the sieving apparatus. The vacuum suction is configured to draw grain particles through the inlet port into the top chamber, generate substantially horizontal airflow in the top chamber via the inlet port; and generate substantially vertical airflow in the top chamber via the plurality of openings, wherein the substantially horizontal airflow and the substantially vertical airflow combine to generate turbulence which fluidizes the grain particles in the upper chamber and prevents blockage of the sieve; and drawing fine grain particles through the sieve and out of the bottom chamber via the first exit port under the vacuum suction and collecting a fine grain particle fr
