Abstract: The invention concerns a mixing vessel (1) for containing a product to be mixed with other content in a receiving vessel (18), said mixing vessel comprising a container (2) and an adapter (3), said container comprising a neck (4) intended to be mounted on a neck of the receiving vessel via the adapter, the neck of the container being a universal neck that can be used on any receiving vessel comprising a neck of any size, said adapter (3) comprising a removable lid (5) for opening the mixing vessel (1) on the receiving vessel (18) such that the product of the mixing vessel and the product of the receiving vessel mix.