Capsule containing a substance for the preparation of a potable beverage by extracting and/or dissolving the substance by means of supplying a fluid under pressure into the capsule, wherein the capsule comprises an aluminum capsule body having a central capsule body axis, said aluminum capsule body being provided with a capsule body bottom, a side wall and an outwardly extending flange comprising a curled outer edge, said outwardly extending flange extending transverse to the central capsule body axis, the capsule further comprising an aluminum cover attached to the outwardly extending flange, the cover hermetically closing the capsule, wherein the capsule further comprises a sealing member at the outwardly extending flange for providing a fluid sealing contact with an enclosing member of a beverage preparation device if the capsule is positioned in the enclosing member of the beverage preparation device and the enclosing member is closed by means of a closing member of the beverage preparation device, such as an extraction plate of the beverage preparation device, such that the outwardly extending flange of the capsule and at least a portion of the sealing member of the capsule are sealingly engaged between the enclosing member and the closing member of the beverage preparation device, wherein the enclosing member of the beverage preparation device comprises an annular element having a central annular element axis and a free contact end, said free contact end of the annular element optionally being provided with a plurality of radially extending open grooves, characterized in that, the sealing member is integral with the outwardly extending flange and comprises a single annular projection comprising a projection top projecting axially towards the capsule body bottom from an inner foot portion racially outside of a flat inner flange portion extending between the capsule body side wall and the projection and an outer foot portion racially inside of a flat outer flange portion extending between the projection and the curled outer edge, and wherein:
- the flat outer flange portion is axially spaced from the flat inner flange portion towards the bottom of the capsule body;
- or
- the flat outer flange portion and the flat inner flange portion are in line and wherein a radially outer wall of said projection is oriented transverse to the flat outer flange portion.