Abstract: The invention relates to a container assembly comprising fluid, and particularly beverage, cooling and/or mixing means. The cooling and/or mixing is achieved by positioning a movable plunger assembly within the container, the base of which defines notional volume variable upper and lower chambers of the container. The base of the plunger is provided with perforations (and optionally, sealable compartments for sugar, milk etc.) adapted to allow pressurised liquid to be urged from the lower chamber to form upwardly directed jets of liquid in the upper chamber. The invention is particularly advantageous because it allows the consumer to selectively cool and/or mix a beverage by means of a plunging and/or twisting action, thus balancing the demand for hot beverages with the dangers of scalding.