Attention 1. The milk could not be long-placed or the lactose will transform to lactic acid which may affect the isolation 2. Excess acetic acid is not allowed. since the acetic acid will accelerate the hydrolysis of lactose1. The milk could not be long-placed, or the lactose will transform to lactic acid, which may affect the isolation. 2. Excess acetic acid is not allowed, since the acetic acid will accelerate the hydrolysis of lactose. Attention