Emerging identity-preserved grain markets depend on avoidance of commingling grain at harvest. Knowledge of where grain resides in a combine, cleaning labor requirements, and resulting purity levels would assist producers. Measurements were made of grain and other material residing in different areas of rotary- and cylinder-type combines in replicated clean-outs during corn and soybean harvest and also in preliminary clean-outs during oat harvest. Concentration of the prior (i.e. commingled) grain was measured in the first grain harvested of the subsequent crop.

Total material remaining in the combine ranged from 84 to 186 lb, 61% of which was whole grain. The greatest amounts of corn and soybean material (17 to 74 lb) were found in the grain tank and rock trap. Intermediate amounts were found in the head or feederhouse, elevators, and at times the cylinder/rotor (soybeans), the unloading auger (soybeans, oats), and rear axle/chopper area. The least amounts were found in the cleaning shoe and straw walkers (cylinder-type machine). Time spent to clean the combine varied from about two hours to seven hours. Cleaning the head, grain tank, threshing rotor/cylinder, and cleaning shoe required more time than other areas. Immediately after cleaning, small amounts of prior (commingled) grain and foreign material, 0.2 to 2.5 lb, were found in the first bushel of subsequent grain harvested. Following clean-outs, commingled grain levels dropped below 0.5% after 20 bu were harvested. Over 14 lb of wheat were found during the first clean-out of a combine following 50 ac of oat harvest (no physical clean-out prior to oat harvest).