Abstract: Flocculation is caused by the protein flop which is encoded by flocculating gene and selectively binds the mannose sugars in the cell wall of other cells.Then cells adhere to form flocs consisting of thousands of cells.The genetic aspects and engineering of the yeast flocculation are reviewed.Factors,such as inorganic ion,nutrients,pH,temperature,ethanol concentration and cellular age,affecting the flocculation are also described