BACKGROUNDCellulosic bioethanol processes involve several steps, all of which require experimental optimisation. A significant aid to this research would be a validated ultra scale-down (USD) model that could be used to perform rapid, wide ranging screening and optimisation experiments using limited materials under process relevant conditions. RESULTSIn this work, the use of 30 mL shaken conical tubes as a USD model for an enzymatic hydrolysis process is established. The approach is demonstrated for the hydrolysis of distillers' dried grains with solubles (DDGS). Results from the USD tubes closely mimic those obtained from 4 L stirred tanks, in terms of the rate, composition and concentrations of sugars released, representing an 80-fold scale reduction. The utility of the USD approach is illustrated by investigating factors that may be limiting hydrolysis yields at high solids loadings. Washing the residual solids periodically during hydrolysis allowed 100% of the available sugar to be hydrolysed using commercially available enzymes. CONCLUSIONThe results demonstrate that the USD system reported successfully mimics the performance of conventional stirred tanks under industrially relevant conditions. The utility of the system was confirmed through its use to investigate performance limitation using a commercially relevant feedstock. (c) 2015 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.