An online fouling monitoring device known as the Mechatronic Surface Sensor (MSS) was applied to a tubular configuration and validated in order to allow a user to identify the nature of the fouling deposits using surface acoustic wave properties, without needing to visualize the fouled surface. This work was based on the formation of simulated milk deposits, with calcium phosphate and protein fouling agents. The results show that by using the system output parameters, such as normalized amplitude and its relationship with the damping factor, it is possible not only to follow the buildup of the deposits, but also to differentiate between the deposits' nature. These parameters showed a clear distinction between a more rigid deposit (e.g., simulated milk ultrafiltrate [SMUF]) and more viscoelastic ones (e.g., WPI or a mixture of SMUF with WPI).