Fuente: WIPO "dairy products" The invention relates to the technical field of dairy product processing, and discloses an expanding culture system for dairy product strains, a sterile online mixing device of the expanding culture system and an expanding culture tank for expanding culture fermentation of the strains. A feeding line is arranged between the sterile online mixing device and the expanding culture tank, and an expanding culture tank feeding valve is mounted on the feeding line; a heat preservation layer is arranged on the periphery of the expanding culture tank, and an ice water inlet valve is arranged on the heat preservation layer so as to cool the expanding culture stock solution in the expanding culture tank; a discharging line is arranged at the other end of the expanding culture tank, and a material quantitative discharging valve and a flow controller are arranged on the discharging line. The method has the effects of reducing strain waste in the production process and reducing the production cost.