To investigate the mechanisms involved in sugar drying, experiments were carried out drying a molasses film with an embedded thermocouple suspended from a microbalance. The heat and mass transfer coefficients for the air film are those applicable in normal humidification theory. The humidity at the molasses surface is the difficult quantity to estimate. In extended drying the surface of the molasses film rapidly becomes depleted in water and the resulting substantial drop in surface humidity controls the rate of drying. In a sugar dryer, the drying is periodic, consisting of about a second of drying followed by a 10-fold period of conditioning, which allows some of the internal water in the molasses film to diffuse to the surface.