there is shown a diagram comparing the h factor for pulp produced according to conventional itc u2122 cooking and the invention the h factor is a function of time and temperature in relation to the delignification process degree of delignification during cooking the h factor is used to control the delignification process of a digester i e maintaining a certain h factor principally leads to the same kappa number of the produced pulp remaining lignin content of the fibre material independent of temperature variations during the cooking in fig5 it is shown that the h factor for pulp produced according to the invention is extremely much lower about 40 50 lower compared to pulp produced according to itc u2122 this means that much lower temperatures may be used for the same retention time in order to reach a certain degree of delignification kappa number and or that smaller vessels for the cooking within a continuous digester can be used and or that a lower kappa number may be achieved with the same kind of basic equipment and or that higher rate of production can be obtained the lower h factor demand is achieved by a high alkali concentration and a low cooking temperature in the concurrent cooking zone which is shown in fig6 which presents one reference itc cook itc 1770 and one cook according to the invention modified itc 1763 as shown the temperature in the counter.