A cap for a bottle includes a first portion, a second portion, and an end piece having a concave body and a hole. The second portion is configured to retain a first ingredient, and the bottle is configured to retain a second ingredient. The first portion may be threadingly secured to the second portion while the second portion plugs the bottle and the end piece is secured to the second portion. Unthreading of the first portion from the second portion causes the first ingredient to fall through the hole and mix with the second ingredient in the bottle.
