Abstract: A beverage ingredient dispenser can include a seal assembly configured to form spillproof seals with the inner surface (I.D.) of a beverage container opening. Additionally, a beverage ingredient dispenser can include a beverage ingredient reservoir containing a beverage ingredient to be mixed with another ingredient for creating a mixed beverage. For example, the beverage ingredient dispenser can include a dried powdered, tablet, or liquid ingredient to be mixed with water contained in a water bottle. The dispenser can also include a sealing mechanism configured to generate spillproof seals with a plurality of different sizes of beverage containers. The dispenser can also include an anchoring mechanism configured to enhance an anchoring of the dispenser to a beverage container.