Abstract: The objective is to develop a method for determining the quality of a liquid product containing polyphenols. The present invention is a method that is a significant improvement over existing methods that use conventional laboratory instrumentation to study the quality of liquid products. The method uses an adsorption cell with a small mirror as a reflecting surface and acts as a substrate for the adsorption of the liquid's polyphenols on its surface. The polyphenol's film thickness is measured by laser ellipsometry. Light from a monochromatic light source is reflected from the thin film of polyphenol, which changes the light's optical properties and are sensed using the principles of ellipsometry. The changes in state of polarized light are translated into graphical illustrations of measured and computed parameters that can be recognized and interpreted as distinctive properties of liquid product quality.