in spite of minor limitations due to membrane fouling and catalyst inactivation, one-step hydrolysis of starch with termamyl enzyme in a continuous recycle membrane reactor appears to be a promising way to produce high DE sugar syrups. In addition to the main advantage over batch process to correctly integrating reaction and separation, this type of system opens up to process engineer tunable performance in terms of conversion, capacity and productivity. In this paper the effects of enzyme concentration and space time have been examined. As a Whole it appears that by increasing these two parameters the conversion is improved; but the capacity and productivity are reduced leading to higher processing costs. Optimisation of enzyme concentration and space time needs that economic criteria are very carefully taken into account.