I have refractive index vs. percent v/v ethyl alcohol in water concentration data from literature. I am following the fermentation progress of 13.5 weight percent cane sugar (C12H22O11) in water using yeast to catalyze. The problem is that even the original sugar solution as measured by a refractometer shows alcohol equivalent v/v concentration of 50 percent and thus interfering with the accurate measurements of the refractive index of the product alone (i.e. concentration of aqueous ethyl alcohol alone). I have measured the alcohol equivalent v/v percent of sugar solutions of various concentrations from 0 to 13.5 weight percent in water. What is a good way to follow the progress of the fermentation process by measuring the alcohol concentration using a refractometer?