The invention relates to a method and an arrangement for admixing powdered substance to heated liquid in a mixing vessel (11). The powdered substance is fed into the mixing vessel via a powder inlet (16) provided in the upper part of the mixing vessel and is made to fall down into heated liquid in the mixing vessel in order to be mixed with this liquid. Dry heated air or other dry gas is blown into the upper part of the mixing vessel above the surface of the heated liquid via one or more gas inlets (25) provided in the mixing vessel in order to form a volume of dry hot air or other dry gas in upper part of the mixing vessel in the area of the powder inlet and thereby prevent vapour from the heated liquid in the mixing vessel from rising to the powder inlet.