This paper describes the application of a non-contact ultrasonic system to food inspection, using electrostatic transducers and signal processing techniques. The system, which operates in through-transmission mode, is used to detect physiochemical changes and density variations in food. One application is to monitor coagulation processes, caused by destabilization in milk-based products. It is shown that the amplitude of the signal varies with time after the pH of such samples was lowered, resulting in destabilisation. Various types of samples of different pH values were used in order to illustrate that the air-coupled system was sensitive to such changes. Non-contact imaging has also been performed to follow this process, during which gel formation could be identified. In addition, changes in oil properties due to temperature variations have also been measured using the non-contact system. The measurements can be achieved without contact to the test samples, and thus has the potential for the rapid inspection of various types of food products. (c) 2005 Elsevier Ltd. All rights reserved.