The presence of foam is an important characteristic of chocolate beverages. In Mexico, which is part of ancient Mesoamerica, foam has been produced since ancient times mainly through two different techniques: by pouring the liquid from one vessel to another and by using the molinillo, which is a chocolate beater currently is widely used. Knowledge regarding the different designs and modes of use of the molinillo has traditionally been empirical. Therefore, the characterisation of the performance of the traditional molinillo is necessary. In this work, the performance of the molinillo during the preparation of a chocolate beverage was characterised through high-speed video, and the foam production at three different levels of immersion (clearance), was measured. Furthermore, the hydrodynamics in the system was analyzed. The tip speed reached approximately 3 m s-1, and a typical forward-backward cycle lasted approximately 300 milliseconds. A small clearance resulted in a high solid dispersion capacity but a limited foam production, whereas a large clearance improved the foam production but exhibited a poor solid suspension. The results quantitatively revealed the scientific basis underlying the empirical ancestral performance of the molinillo in the dispersion of cocoa solids, the promotion of liquid (water)-liquid (cocoa fat) mixing, and the production of foam.