Strength delivery of softwood chemical pulps has been previously studied extensively without being able to define the underlying morphological factors such as the initiation of weak points within the fibres. In this study an industrial kraft cooking process was simulated with the use of a laboratory batch digester and applying compression and shear forces to the chips during cooking. The results of cooks of pine, to kappa 30 and 45, were significantly affected when subjected to shearing forces during the last 15 minutes of the cook. The typical behaviour of a softwood industrial pulp viz. being more difficult to beat and having lower tear index at comparable tensile index around 90 Nm/g, when compared to a laboratory pulp produced from the same raw material, was obtained. The mechanically treated pulps also had substantially higher dewatering ability reflecting a more collapsed cell structure. Pure compression loading of chips during cooking did not induce these detrimental effects.