A system and method for quantifying opaque inhomogeneities within a fluid sample. The system uses an optical lens system to focus a light beam onto a stage where the sample is introduced. The light beam is directed onto the sample in a pattern such that the intensity of transmitted light is measured as a function of path length. A photo detector measures the transmitted light through the sample. Fluctuations in transmitted light intensity are then correlated with detection of opaque inclusions in the sample. The system also includes an automated program which utilizes these optical concentration measurements to determine the fouling potential of visbroken tars, and regulates the introduction of chemical inhibitors into a visbreaker unit to improve the yield of light streams and/or economic value of product.