A propeller for a digestion tank mixer, wherein the propeller comprises a hub and at least two blades, wherein each blade comprises: - a thrust side surface and a suction side surface, - an inner edge fixedly connected to the hub and an outer edge located at a distance from the hub, and - a leading edge extending from the inner edge to the outer edge, and a trailing edge extending from the inner edge to the outer edge, wherein for each blade there is an outer geometrical plane that is parallel to a center axis of the propeller, perpendicular to a radius of the propeller and intersects both the leading edge and the trailing edge, and comprises at least one of the intersection between the outer edge and the leading edge and the intersection between the outer edge and the trailing edge, there is an inner geometrical plane that is parallel to the outer geometrical plane and that is tangent to the hub, and there is a radial distance between and perpendicular to the outer geometrical plane and the inner geometrical plane, wherein at each intermediate geometrical plane located between and parallel to the outer geometrical plane and the inner geometrical plane, the blade has: - an arc-shaped cross section that extends between the leading edge and the trailing edge and that is concave on the thrust side, and - a chord that extends between the leading edge and the trailing edge, characterized in that an angle (α) between the chord and a radial plane of the propeller, is equal to or greater than 25 degrees and equal to or less than 45 degrees in each intermediate geometrical plane taken along the entire radial distance, and that the ratio between an arc-height between the chord and the thrust side surface and the length of the chord, AH:C, is equal to or greater than 0,08 and equal to or less than 0,15 in each intermediate geometrical plane taken along the entire radial distance. - a thrust side surface and a suction side surface, - an inner edge fixedly connected to the hub and an outer edge located at a distance from the hub, and - a leading edge extending from the inner edge to the outer edge, and a trailing edge extending from the inner edge to the outer edge, wherein for each blade there is an outer geometrical plane that is parallel to a center axis of the propeller, perpendicular to a radius of the propeller and intersects both the leading edge and the trailing edge, and comprises at least one of the intersection between the outer edge and the leading edge and the intersection between the outer edge and the trailing edge, there is an inner geometrical plane that is parallel to the outer geometrical plane and that is tangent to the hub, and there is a radial distance between and perpendicular to the outer geometrical plane and the inner geometrical plane, wherein at each intermediate geometrical plane located between and parallel to the outer geometrical plane and the inner geometrical plane, the blade has: - an arc-shaped cross section that extends between the leading edge and the trailing edge and that is concave on the thrust side, and - a chord that extends between the leading edge and the trailing edge, characterized in that an angle (α) between the chord and a radial plane of the propeller, is equal to or greater than 25 degrees and equal to or less than 45 degrees in each intermediate geometrical plane taken along the entire radial distance, and - an arc-shaped cross section that extends between the leading edge and the trailing edge and that is concave on the thrust side, and - a chord that extends between the leading edge and the trailing edge, characterized in that an angle (α) between the chord and a radial plane of the propeller, is equal to or greater than 25 degrees and equal to or less than 45 degrees in each intermediate geometrical plane taken along the entire radial distance, and that the ratio between an arc-height between the chord and the thrust side surface and the length of the chord, AH:C, is equal to or greater than 0,08 and equal to or less than 0,15 in each intermediate geometrical plane taken along the entire radial distance.