The invention relates to a rotary stirring device (6) of a beverage preparation machine, comprising a rotary tool (7) about an axis A and a pipe (24) for conveying hot water and / or steam comprising a hollow part (18) of a drive shaft (12) which communicates with a tubular part (20) extending along the axis A between a first end (22) coupled to the rotary tool and a second end (23) coupled to said hollow part by means of a magnetic coupling device (25) configured to generate a magnetic attraction force along the axis A between the drive shaft (12) and said second end (23). The magnetic coupling device comprises a metal member (30) arranged on said second end (23) and formed by an internal ring (32) made of stainless steel resistant to corrosion in a vapor environment and an external ring (31) made in a ferromagnetic material. The internal ring (32) is intended to slide on said hollow part (18) which is made of stainless steel resistant to corrosion in a vapor atmosphere, when the coupling is produced.
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