Combinatorial peptide ligand libraries (CPLLs) have been adopted for harvesting and identifying traces of casein (used as a fining agent) present in white wines. Although minute amounts (200µL) of CPLL beads are added to the entire content of a wine bottle (750mL), they are able to sequester with high efficiency (up to 80%) residual traces of casein, permitting a signal “amplification” of at least 5000-fold. It is here demonstrated that as little as 1µg/L of casein can be efficiently detected in white wines, a major improvement over previous investigations in which the lower detection limit had been estimated at 100µg/L. The fact that such very low levels of fining agents can still be detected in treated white wines should be taken into consideration by winemakers in labelling their products and by EC rulers in issuing proper regulations.