the cooking process superfluous transport liquid may be drawn off with a strainer in the top and then be reintroduced into a flow 2 to the feeding system the feeding system may either be a conventional tap or a sluice feeding valve or pumps or in some cases a prior filled impregnation vessel which pressurizes the wood chips mixture before being transferred to the top of the digester in the figure the flows of cooking liquors in concurrent treatment zones of the digester are indicated with df down flow and counter current treatment zones with uf up flow and the flow of wood chips is indicated with cf chip flow in the upper part of the digester a first impregnation zone may be provided down to the strainer 11 b and optionally a cooking circulation 11 a 18 a may be provided prior to this in which circulation the cooking liquor is drawn off through the strainer 11 a and reintroduced to the center of the digester via a conventional central tube with pipe 18 a in the first impregnation zone the wood chips are impregnated with an impregnation liquid at a temperature that is above 80 u00b0 c but at the same time below the cooking temperature by at least 20 u00b0 c the impregnation.