for recirculation to the first vessel 80 either without further treatment or after having been mixed with a stream of white liquor 92 and conveyed into the first vessel in the depicted embodiment of fig2 intermediate the top and bottom ends of the vessel there are provided a wash circulation sub system 66 a lower extraction location 68 and a trim circulation sub system 70 an upper extraction location 72 is associated with the trim circulation sub system the preferred embodiment of the method of the present invention was employed with the digester depicted in fig1 in this single vessel continuous digester cooking liquor rich in dissolved calcium of u02dc 40 u2013 120 ppm is withdrawn from the first row of screens of the upper cook circulation screen set at a flow rate of 0 10 u2013 0 50 gpm for each ton per day production rate or gpm tpd factor for example for a pulp production rate of 750 tons per day 0 1 u2013 0 5 times 750 yields 75 u2013 350 gallons per minute gpm a mixture of cold blow filtrate and wash extraction streams the sum of which is about the same as the upper extraction flow and the concentration of dissolved calcium is less than 40 ppm is added to the top of the digester via the makeup liquor pump in this example up to about 45 of the total dissolved calcium may be removed from the digester system significantly reducing the tendency of calcium scaling on digester screens and cooking heaters in a further example of the preferred embodiment of the method of the present invention employing a single vessel digester as depicted in fig1 cooking liquor with u02dc 100 ppm.