A container assembly comprising: a container having a first end, a second end, and a sidewall extending therebetween and defining a container interior, the container defining a container longitudinal axis; a first closure sealing the first end of the container; and a second closure sealing the second end of the container; characterized in that the container assembly further comprises: a first mixing element protruding into the container interior, the first mixing element extending from a portion of the first closure, whereby, with the container rotated about the container longitudinal axis, the first mixing element forms at least one vortex (w, x) which effectuates mixing of a first substance provided within the container interior and a second substance provided within the container interior; and a second mixing element (64, 70, 80, 90) protruding into the container interior, the second mixing element extending from a portion of the second closure, whereby, with the container rotated about the container longitudinal axis, the first mixing element and the second mixing element form the at least one vortex which effectuates mixing of the first substance and the second substance within the container assembly. a container having a first end, a second end, and a sidewall extending therebetween and defining a container interior, the container defining a container longitudinal axis; a first closure sealing the first end of the container; and a second closure sealing the second end of the container; characterized in that the container assembly further comprises: a first mixing element protruding into the container interior, the first mixing element extending from a portion of the first closure, whereby, with the container rotated about the container longitudinal axis, the first mixing element forms at least one vortex (w, x) which effectuates mixing of a first substance provided within the container interior and a second substance provided within the container interior; and a second mixing element (64, 70, 80, 90) protruding into the container interior, the second mixing element extending from a portion of the second closure, whereby, with the container rotated about the container longitudinal axis, the first mixing element and the second mixing element form the at least one vortex which effectuates mixing of the first substance and the second substance within the container assembly. a first mixing element protruding into the container interior, the first mixing element extending from a portion of the first closure, whereby, with the container rotated about the container longitudinal axis, the first mixing element forms at least one vortex (w, x) which effectuates mixing of a first substance provided within the container interior and a second substance provided within the container interior; and a second mixing element (64, 70, 80, 90) protruding into the container interior, the second mixing element extending from a portion of the second closure, whereby, with the container rotated about the container longitudinal axis, the first mixing element and the second mixing element form the at least one vortex which effectuates mixing of the first substance and the second substance within the container assembly.