The fermenter may be installed horizontally, however, there is no effect on efficiency of the fermenter even when installed vertically. Fermenters can be stacked one above other. The present invention further focuses on a system of aeration ,a very important factor in large fermenters. In a fermenter with a high microbial population density, there is a tremendous oxygen demand by the culture, but oxygen being poorly soluble in water hardly transfers rapidly throughout the growth medium. The tubular fermenter encompasses within its body, an aeration line for a controlled aeration and a means of homogenous distribution of air and other material inside the fermenter. The said means is an impeller. The present tubular fermenter has a helical impeller. Helical impellers are specially used when the density of the fermentation medium is higher, to provide a uniform mixing and to eliminate “dead” zones. Helical blades efficiently create a more homogenous and uniform mixing at a faster rate and with lower power consumption. The invention further intends to overcome the economics of continuous preparation of yeast inoculum for running the continuous process. The wastage of the yeast culture during downstream processing is addressed by retaining the yeast cells in the fermentation media, thereby increasing the yield of bioethanol. The invention describes a rotating perfusion system enabled to retain 170 the yeast inside the tubular fermentor and allow a continuous outflow of a filtrate product. The problem of contamination of the fermentation media is also overcome as any contaminating bacterial culture is filtered out along with the filtrate. The tubular fermentor is enabled for a continuous fermentation. Sterile medium is added continuously at a controlled flow rate so that the biologically active yeast inoculum remains functional for 1 to 3 months. The process parameters are controlled by a computerized control unit.