A 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 (2; 102), said capsule (2; 102) comprising: an aluminum capsule body having a central capsule body axis, said aluminum capsule body comprising a bottom, a sidewall, an outwardly extending flange (20; 120) and a sealing structure at said flange (20; 120); and a cover sheet (14; 114) attached to said flange (20; 120) and hermetically closing off the capsule (2; 102); wherein said sealing structure is deformable for providing a fluid sealing contact with an annular end surface of an enclosing member of a beverage preparation device if the capsule (2; 102) is positioned in said enclosing member and said 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, at least portions of said flange (20; 120) and said sealing structure being clamped between said annular end surface and said closing member; said annular end surface optionally being provided with a plurality of radially extending open grooves; wherein said sealing structure includes a deformable sealing ring portion of said flange (20; 120), said sealing ring portion projecting axially from base portions of said flange (20; 120), to which said cover sheet (14; 114) is attached, on a side of said base portion opposite of said cover sheet (14; 114), said deformable sealing ring portion comprising: an inner wall portion extending from and contiguous with an inner base portion of said flange (20; 120); an outer wall portion extending from and contiguous with an outer base portion of said flange (20; 120), said outer wall portion being located outward of and spaced from said inner wall portion; and a bridge portion (48; 148) interconnecting said inner wall portion and said outer wall portion, said bridge portion (48; 148) being located axially spaced from said base portions of said flange (20; 120); characterized by at least one support member (49; 149) between said inner and outer wall portions (46, 47), wherein the support member supports the bridge portion (48; 148). an aluminum capsule body having a central capsule body axis, said aluminum capsule body comprising a bottom, a sidewall, an outwardly extending flange (20; 120) and a sealing structure at said flange (20; 120); and a cover sheet (14; 114) attached to said flange (20; 120) and hermetically closing off the capsule (2; 102); wherein said sealing structure is deformable for providing a fluid sealing contact with an annular end surface of an enclosing member of a beverage preparation device if the capsule (2; 102) is positioned in said enclosing member and said 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, at least portions of said flange (20; 120) and said sealing structure being clamped between said annular end surface and said closing member; said annular end surface optionally being provided with a plurality of radially extending open grooves; wherein said sealing structure includes a deformable sealing ring portion of said flange (20; 120), said sealing ring portion projecting axially from base portions of said flange (20; 120), to which said cover sheet (14; 114) is attached, on a side of said base portion opposite of said cover sheet (14; 114), said deformable sealing ring portion comprising: an inner wall portion extending from and contiguous with an inner base portion of said flange (20; 120); an outer wall portion extending from and contiguous with an outer base portion of said flange (20; 120), said outer wall portion being located outward of and spaced from said inner wall portion; and a bridge portion (48; 148) interconnecting said inner wall portion and said outer wall portion, said bridge portion (48; 148) being located axially spaced from said base portions of said flange (20; 120); characterized by at least one support member (49; 149) between said inner and outer wall portions (46, 47), wherein the support member supports the bridge portion (48; 148). an inner wall portion extending from and contiguous with an inner base portion of said flange (20; 120); an outer wall portion extending from and contiguous with an outer base portion of said flange (20; 120), said outer wall portion being located outward of and spaced from said inner wall portion; and a bridge portion (48; 148) interconnecting said inner wall portion and said outer wall portion, said bridge portion (48; 148) being located axially spaced from said base portions of said flange (20; 120); characterized by at least one support member (49; 149) between said inner and outer wall portions (46, 47), wherein the support member supports the bridge portion (48; 148).