The Veratox for Casein Allergen test is a sandwich enzyme-linked immunosorbent assay (S-ELISA). Casein residue is extracted from samples with a buffered salt solution (Phosphate Buffered Saline, or PBS) by shaking in a heated water bath. Extracted casein residue is sampled and added to antibody-coated wells (capture antibody) where it binds to the antibody during an incubation. Any unbound residue is washed away and a second antibody (detector antibody), which is enzyme labeled, is added. The detector antibody binds to the already bound casein residue. After a second wash, the substrate is added. Color develops as a result of the presence of bound detector antibody. Red Stop reagent is added and the color of the resulting solution is observed. The test is read in a microwell reader to yield optical densities. The optical densities of the controls form a standard curve, and the sample optical densities are plotted against the curve to calculate the exact concentration of allergen.