The invention concerns a beverage preparation assembly (1) comprising: —a container (2) for storing a water soluble beverage powder, said container comprising a tank (21) and a powder outlet (22), —a dissolution chamber (3) for preparing a beverage from the water soluble beverage powder and a diluent, said dissolution chamber comprising at last one diluent inlet (31) and a beverage outlet (32), —a chute (4) for guiding the water soluble beverage powder from the powder outlet (22) of the container to the dissolution chamber (3), —an air outlet (5) configured for evacuating air from the dissolution chamber (3), wherein the powder outlet (22) is connected to the chute (4) by a conduit (6), and wherein the powder outlet (22), the conduit (5), the chute (4) and the dissolution chamber (3) are connected together through airtight connections, and wherein said assembly comprises an air inlet (8), said air inlet being positioned above the chute (4) only.