Abstract: A method and a system for determining gel firmness values from inline optical measurements. The method comprises:—emitting light into a gel which is hardening to develop firmness;—optically detecting light coming from said gel to collect light data;—calculating a value of a rheological variable from the collected light data;—defining a mathematical model of the evolution in time of said rheological variable;—defining a mathematical model of the evolution in time of an optical variable generated from a light generation mechanism responsible for generating said detected light;—combining both mathematical models in order to obtain an expression which does not include time and which relates said rheological variable with said optical variable; and—introducing said collected light data into said expression to calculate said value of the rheological variable. The system comprises means for implementing the method of the invention.