TECHNOLOGY FOCUS - BIOLOGY - Preferred Process: The cultivation is carried out under simple sugar depleted conditions of having an amount of added simple sugar or simple sugars in the range of 0-10 wt.% of the sugar depleted cultivation environment on a dry basis for a portion of the cultivation time which is at least 50% of the cultivation time. The solid composition is obtained from the second pre-treated ligno-cellulosic biomass by either (a) hydrolyzing at least a fraction of the second pre-treated ligno-cellulosic biomass in the presence of a hydrolysis catalyst, to produce a hydrolyzed composition comprising the solid composition and a solution of water and soluble sugars and (b) removing at least 50% of the solution of water and soluble sugars from the hydrolyzed composition, or (a1) the step (a) as above per se to produce a hydrolyzed composition comprising complex sugars and lignin and the solution of water and soluble sugars, (b1) converting at least a fraction of the soluble sugars in the hydrolyzed composition to produce a converted composition comprising at least one sugar derived product, and the solid composition, and (c1) removing a fraction of the at least one sugar derived product. The step (b) is done by at least one method of decantation, sedimentation, centrifugation, filtration, press filtration or washing. The step (c1) is done by at least one method of decantation, sedimentation, centrifugation, filtration, press filtration, washing, evaporation or distillation. In the process, simple sugar is not added in the sugar depleted cultivation environment. The first enzyme is harvested by separating the sugar depleted cultivation environment into at least a harvested composition comprising at least a fraction of the amount of the first enzyme, and an exhausted composition comprising at least a fraction of an amount of solid residue of the solid composition. The first enzyme is further used to hydrolyze the first ligno-cellulosic biomass and the first ligno-cellulosic biomass and the second pretreated ligno-cellulosic biomass both comprise ligno-cellulosic biomass derived from the group consisting of the same grass genus and the same grass species. Preferred Components: The hydrolysis catalyst comprises a second enzyme or enzymes mixture and is hydrogen ions, organic acids or inorganic acids. The conversion of the hydrolyzed composition is carried out by fermentation process. The sugar derived product comprises ethanol. The portion of the cultivation time under simple sugar depleted conditions and sugar starved conditions is at least 75%, preferably at least 98% of the cultivation time. The amount of added simple sugar or sugars is in the range of 0-5%, preferably 0-1 wt.% of the sugar depleted cultivation environment on a dry basis. The total amount of complex sugars in the exhausted composition is present in a range of 0-30 wt.%, preferably 0-2.5 wt.% on a dry basis. EXAMPLE - No suitable example given.