A membrane for sealing an open spout of a food package comprises a central circular disc member, an outer annular disc member connected to the central circular disc member along its inner periphery at a connection angle, and a resilient tubular portion extending between a first open end and a second end being connected to the outer annular disc member, the diameter of the second end being smaller than the outer diameter of the annular disc member, wherein the annular disc member is pivotable relative the central circular disc member for increasing the diameter of the second end of the tubular portion by changing the connection angle.