An extraction unit (1) has a piercing device (10) for piercing a capsule (20). The piercing device includes: a base (14) with peripheral sections, such as generally straight peripheral sections (14a, 14b, 14c1, 14c2); a plurality of blades (11a, 11b, 11c) that protrude from the base along a longitudinal direction (12a′, 12b′, 12c′), each blade extending laterally generally along one of the peripheral sections (14a, 14b, 14c1); and a plurality of assembly members (15a, 15b, 15c), each assembly member (15a, 15b, 15c) extending and protruding from one of the peripheral sections (14b,14c2). At least one assembly member (15a, 15c) of said assembly members (15a, 15b, 15c) is located at least in part generally in the longitudinal direction (12b′, 12c′) under a corresponding blade (11b, 11c).