Continuous culture is called an open system because the constant internal condition is maintained throughout the culture by adding nutrition, microbes and removing waste. Here the cell volume and cell culture are maintained constant by adding a fresh and sterile medium. There are only two phases in the continuous culture system: lag and log phase. In the log the phase growth is rapid.In this type of fermentation growth limiting nutrients can be maintained at a steady concentration, which permits the growth of microbes at a submaximal rate.