Abstract: A method for optimization of a fed batch hydrolysis process wherein the hydrolysis time is minimized by controlling the feed addition volume and/or batch addition frequency of the prehydrolysate and optionally also the enzyme feed. The increase over time in hydrolysate consistency and volume and/or concentration of sugars released in the reactor, so that the enzymatic hydrolysis is controlled, significantly reduces the impact of cellulase feedback inhibition, especially for enzyme contents lower than 0.5%. The overall time to reach conversion of the total prehydrolysate feed is reduced significantly where the batch addition frequency is equal to one batch each time 70% to 90%, preferably 80%, conversion of the previous batch is reached in the reaction mixture. At an enzyme load of 0.3% in the reaction mixture, the optimum frequency each time 80% conversion was reached was found to be one batch every 105 minutes.