As most recombinant strains cannot tolerate high concentrations of ethanol, an alternative solution to this problem could be the simultaneous removal of ethanol as it is produced. As ethanol is removed from the fermentation broth, the culture is relieved of the ethanol toxicity effects and as a result produces more ethanol. As ethanol is produced, the level of sugar present in the reactor is reduced. To replace sugar, the reactor is fed with a concentrated sugar solution at a rate that is compatible to sugar utilization by the microbe for ethanol production. This process is called fed-batch and is applicable to systems where the use of a concentrated sugar solution is toxic to the culture. It should be noted that most lignocellulosic hydrolysates contain low sugar levels, hence a combination of lignocellulosic hydrolysate supplemented with glucose to raise the sugar level is an approach to consider. Alternately, cultures that are not inhibited by high sugar concentrations can be used in batch systems with simultaneous product recovery. In such systems all the sugars present in the bioreactor are converted to a final product. Application of these simultaneous product recovery techniques would reduce reactor size, process stream volume, and result in energy-efficient removal of final product. Use of these techniques for butanol fermentation has been successfully demonstrated in labo­ratory scale reactors (Qureshi 2009). Two of the most common technologies that can be used for product recovery include gas stripping and pervaporation. Gas stripping can be performed using fermentation gases (CO2 in the case of ethanol production, and CO2 plus H2 in the case of the butanol fermentation). The use of pervaporation requires a selective membrane that allows diffusion of biofuel only and restricts water transport across the membrane.