Circulation cleaning presents many opportunities for advancement in liquid food handling systems, but the effectiveness commonly must be evaluated by means other than visual inspection. To study this problem of evaluation, a laboratory system was developed to simulate the soiling and cleaning process of a commercial high-temperature short-time pasteurizer unit. Proof of similarity was obtained by determining quantity of soil at various cleaning intervals and through qualitative examination of the soil with thin-layer chromatography, gas liquid chromatography, and infrared spectroscopy. Lipoidal materials were found to be most resistant to alkaline cleaning. Material removed near the end of the cleaning cycle and material removed by ether rinse of the equipment after the cleaning cycle were similar to milkfat in the milk used for soiling and to the residues recovered from early intervals of cleaning. The removal process for lipoidal material was not attributable to saponification, because little saponification occurred with temperature and alkali concentration associated with circulation cleaning. Data in this paper indicated directions for further work toward criteria of cleaning efficiency and effectiveness.