Research on fouling detection in pipes in the foods industry using acoustics and ultrasonics could-provide efficient and cost effective solutions. Fouling is the build up of fouled food product, corrosion, or baked on food product on the inside wall of a pipe or a plate. The existence of fouling can create unnecessary demands on pumping machinery, can decrease the efficiency of heat flow into the fouled pipes, and can decrease the product quality and/or safety. Early detection and quantification of fouling extent can reduce costs incurred due to wear on the machinery, maintenance of the pipes, and production down time. Two acoustic methods are investigated for their pipe fouling detection potential: guided wave ultrasonics and acoustic impact. The guided wave method relates energy loss to viscous or semi-solid loading on a plate or pipe. Acoustic impact relies upon changes in wave velocity and attenuation to signal the existence of fouling. The basic principles of each method are presented, followed by experimental results, advantages and disadvantages of each, and recommendations for future research. (C) 2002 Elsevier Science Ltd. All rights reserved.