Spray-drying of milk in a Leaflash dryer was studied in relation to volatile aroma loss in drying and during storage of the powders. Diacetyl was used as the volatile model, and the contribution of the various milk constituents to retention was determined. Proteins retain more diacetyl than does lactose or fat. Conditions leading to a powder with more amorphous lactose result in higher diacetyl loss during drying. The rate of diacetyl loss during storage depended on relative humidity and on the T -T, parameter and was strongly enhanced by crystallization of amorphous lactose.