A plug-flow fermentation device for receiving a fermentation material and for fermentation of the fermentation material, the plug-flow fermentation device comprising: a plug-flow fermenter; and a stirring device located in the plug-flow fermenter, the stirring device comprising: a shaft rotatable about an axis of rotation, the axis of rotation being parallel to an axial direction; a plurality of stirring elements including a first stirring element, a second stirring element and a third stirring element; wherein the first stirring element is a boundary stirring element defining an axial extent of a stirring volume covered by the stirring device, wherein the first stirring element is located in a discharge region of the plug-flow fermenter or the first stirring element is located in an input region of the plug-flow fermenter; the second stirring element is a nearest neighbor of the first stirring element in the axial direction; the third stirring element is a next-nearest neighbor of the first stirring element in the axial direction; and in the axial direction the second stirring element has a maximum width which is smaller than a maximum width of the first stirring element and which is larger than a maximum width of the third stirring element; the plurality of stirring elements further comprising two further, axially neighboring stirring elements (110-4, 110-5) defining in the axial direction a first minimum distance therebetween; the first stirring element and the second stirring element defining in the axial direction a second minimum distance therebetween; and wherein the first minimum distance is larger than the second minimum distance. a plug-flow fermenter; and a stirring device located in the plug-flow fermenter, the stirring device comprising: a shaft rotatable about an axis of rotation, the axis of rotation being parallel to an axial direction; a plurality of stirring elements including a first stirring element, a second stirring element and a third stirring element; wherein the first stirring element is a boundary stirring element defining an axial extent of a stirring volume covered by the stirring device, wherein the first stirring element is located in a discharge region of the plug-flow fermenter or the first stirring element is located in an input region of the plug-flow fermenter; the second stirring element is a nearest neighbor of the first stirring element in the axial direction; the third stirring element is a next-nearest neighbor of the first stirring element in the axial direction; and in the axial direction the second stirring element has a maximum width which is smaller than a maximum width of the first stirring element and which is larger than a maximum width of the third stirring element; the plurality of stirring elements further comprising two further, axially neighboring stirring elements (110-4, 110-5) defining in the axial direction a first minimum distance therebetween; the first stirring element and the second stirring element defining in the axial direction a second minimum distance therebetween; and wherein the first minimum distance is larger than the second minimum distance. a shaft rotatable about an axis of rotation, the axis of rotation being parallel to an axial direction; a plurality of stirring elements including a first stirring element, a second stirring element and a third stirring element; wherein the first stirring element is a boundary stirring element defining an axial extent of a stirring volume covered by the stirring device, wherein the first stirring element is located in a discharge region of the plug-flow fermenter or the first stirring element is located in an input region of the plug-flow fermenter; the second stirring element is a nearest neighbor of the first stirring element in the axial direction; the third stirring element is a next-nearest neighbor of the first stirring element in the axial direction; and in the axial direction the second stirring element has a maximum width which is smaller than a maximum width of the first stirring element and which is larger than a maximum width of the third stirring element; the plurality of stirring elements further comprising two further, axially neighboring stirring elements (110-4, 110-5) defining in the axial direction a first minimum distance therebetween; the first stirring element and the second stirring element defining in the axial direction a second minimum distance therebetween; and wherein the first minimum distance is larger than the second minimum distance.