Abstract: A retrofit infuser may be configured to be used with a drinking container to allow material, held within the infuser, to be infused within a liquid of the drinking container. The material may be fruits, vegetables, teas, coffee beans, coffee grounds, or other food and drink related items. The infuser may include a lid. The lid may be configured to removably secure the infuser within a neck of the drinking container or to float atop a liquid in the drinking container. The infuser may include a cage configured to hold the material to be infused and to allow the material to be infused into the liquid of the drinking container. The cage may be configured to be removably secured within the lid of the infuser. The infuser may further be configured to removably secure to a straw of the drinking container.