This paper describes the application of a non-contact ultrasonic system to measure the sugar content and viscosity of reconstituted orange juice. The system, which operates in either pulse-echo (PE) or transmission-through (TT) mode, detects the above two factors using responsive velocity of ultrasound and power attenuation. Experimental results of both modes show that the power attenuation is ineffective for such a purpose, and that the velocity of ultrasound tends to respond linearly to sugar content and exponentially to viscosity. The velocity exhibits a high linear correlation with Brix in orange juice, r = 0.994 in PE mode. (c) 2007 Elsevier Ltd. All rights reserved.