An apparatus and method for defoaming aerobic fermentation cultures is provided, where the amount of liquid culture medium used is greater than that in conventional aerobic cultures (70% or more of the total capacity of the culture tank) without lowering the productivity of the intended, desired product. In the present apparatus and method, a device for separating vapor from liquid of a foam is in fluid communication with the fermentation tank, a device for condensing residual liquid of the vapor received from the separating device is in fluid communication with the separating device, and a sensor for detecting foams is provided in a location along the fluid communication pathway. In the defoaming apparatus, an optional defoaming device is provided, which may be based on either a rotary body rotating at a high speed by use of an electric motor which beats the foams, or on a centrifugal atomizer. The defoaming device may be provided between the vapor-liquid separating device and the condensing device.