A closure assembly for a bottle including a cage, a closure cap, and a sealing nut. The cage includes a side wall with an inner surface including a first annular relief and a second annular relief spaced so as to form a seat for a collar of the bottle. The closure cap includes a head and a shank. The sealing nut includes a side wall. The inner surface of the side wall of the cage includes one or more retaining teeth for retaining the head of the closure cap. The retaining teeth are cantilevered and inclined with respect to the inner surface of the side wall of the cage. Opposite the retaining teeth a recess is provided within which the teeth can be retracted, so that the head of the sealing cap can be pushed towards the base of the cage.