Impurity inspection should pay attention to organic matters other than rice, including foreign grains and shriveled grains. Rice that has no use value, such as discoloration or deterioration due to serious diseases, damage, mildew or other reasons, is an impurity. 1. Inspection of impurities in large samples: 500g samples are screened twice according to the standard, and then the undersized materials and the large impurities selected from the undersized materials are combined and weighed. During inspection, the undersize should be cleaned up. 2. Small sample impurity inspection: take about 50 grams of samples from samples with large impurities, pick out impurities and weigh them according to standards. When checking, pick out the flat lines and press them with your fingers. If you feel that there are no grains of rice, it is flat and classified as impurities. 3. Total impurity inspection: The total impurity is the sum of large sample impurities and small sample impurities, expressed by mass fraction.