Paper recycling industries are oriented towards re-use and sustainability. These effects are combined in different ways to achieve the requirements on printing and writing papers. Biodeinking is an alternative analysed in this study. Cellulase uses improve ink detachment from old newspapers giving similar or better results when cellulase is used in place of classical chemicals. Cellulase needs an optimal contact time with the pulp suspension. Ink detachment can also be optimised by means of defibering efficiency and specific energy consumption. Increasing the consistency and decreasing the repulping time enhance savings and therefore sustainability. These two parameters are analysed in terms of shear factor lambda. (C) 2002 Elsevier Science Ltd. All rights reserved.