In-line Measurement of Color and Total Phenolics during Red Wine Fermentations Using a Light Emitting Diode Sensor

A reduced cost colorimeter for tracking total phenolics and color during fermentation has been developed. The colorimeter uses multiple light emitting diodes (LEDs) spanning the ultraviolet and visible spectrum to make absorbance measurements. The performance of phenolic sensor was evaluated by analyzing fermentation samples collected from multiple red wine fermentations performed in the UC Davis Robert Mondavi Institute during the 2012 Season. The study confirmed that the LED phenolic sensor measurements strongly correlate with measurements performed with a reference UV-Vis spectrometer. A high correlation of 0.98 was found for the 280 nm total phenolic measure while a 0.94 coefficient was found for the 525 nm color measurement. The high correlation suggests that quality absorbance measurements are made even with the use of fixed spectral bandwidth (FWHM less than 10 nm) LED sources. A noise analysis characterized the performance of the transimpedance and switched integrator front-ends. The switched integrator has superior noise performance allowing quantification of small photocurrents generated from the UV LED sources. The sensor concept provides a visible option for performing inline measurements to track the evolution of phenolic content and color during red wine fermentations.