ABSTRACT This article demonstrates the importance of feed condition upon filtration performance as a result of variations in fouling mechanism and cleaning efficiency during the clarification of black tea liquor by ultrafiltration. The filters studied were (1) FP and (2) RC ultrafiltration membranes. Specific fouling resistances, apparent membrane rejections and cleaning efficiencies were analyzed for variations in feed concentration, TMP, temperature, ionic strength and calcium content. Concentration polarization contributed predominantly to the increased total fouling resistance of both membranes as feed concentration was increased, although there was no extra effect upon deposit formation on the RC membrane, whereas rinsable fouling deposit did increase on the FP membrane because of slightly stronger interaction of the foulant with the membrane surface. Increasing the ionic strength increased the total fouling resistance, thus reducing performance while decreasing the severity of deposition fouling as a result of increased concentration polarization. Addition of calcium to the feed stream caused a significant increase in irreversible fouling deposition because of polar group–calcium complexation (bridging). This deposition could not be adequately removed by using standard sodium hydroxide cleaning protocols, or by the addition of surfactants and chelating agents. PRACTICAL APPLICATIONS The nature of complex feeds and membrane filtration usually results in a progressive flux decline that has a marked effect upon the process economics and viability. The effect of black tea feed condition upon ultrafiltration as a clarification method is reported in this article. Membrane–foulant interactions and overall performance are discussed and are relevant to the optimization and clarification of black tea and other protein/polyphenol containing beverages during industrial processing in factory operation. Although cleaning of membranes is inevitably required during filtration of such a complex feed, an understanding of fouling can help reduce the frequency and environmental impact of cleaning in industrial practice.