The production of acidified milk powders by spray drying is challenging due to particle deposition on the dryer surface, which reduces yield, and may impair product quality. The composition, especially lactic acid concentration, and powder particle surface properties, are important in this context. This study explored the possibility of monitoring the drying process using vibrational spectroscopy techniques such as near-infrared (NIR), attenuated total reflection (ATR) and Raman imaging. The results showed that these techniques provide complementary qualitative measurements regarding the composition of acidified milk powders that are useful for understanding and controlling their production. Raman imaging revealed lactic acid surface composition providing better understanding of wall deposition during spray drying. NIR and ATR provided information about the composition and molecular structural changes in powders occurring during the prolonged exposure of powder to the high drying temperature, which may be applicable for on-line and at-line process control, respectively.