NEW TOOL FOR SIMULTANEOUS MEASUREMENT OF OXYGEN CONSUMPTION AND COLOUR MODIFICATIONS IN WINES

Abstract

Measuring the effect of oxygen consumption on the colour of wines as the level of dissolved oxygen decreases over time is very useful to know how much oxygen a wine is able to consume without significantly altering its colour. The changes produced in wine after being exposed to high oxygen concen-trations have been studied by different authors, but in all cases the wine has been analysed once the oxygen consumption process has been completed. This work presents the results obtained with the use of an equipment designed and made to measure simultaneously the level of dissolved oxygen and the spectrum of the wine, during the oxygen consumption process from saturation levels with air to very low levels, which indicate the total consumption of the dosed oxygen.

For this purpose, this equipment has been designed, built and prepared and has been validated with the measurement of red wines made from different grape varieties.

The equipment built has 2 mm quartz cuvettes for the measurement of the spectrum in the visible with a spectrophotometer and a sensor for the simultaneous measurement of dissolved oxygen with a luminescent measurement system, both measurements were carried out every 15 minutes during oxy-gen consumption. The tightness of the cuvettes during the process of measuring the kinetics of oxygen consumption was evaluated, as well as the reproducibility of the measurements of both parameters.

The results of this study show that the equipment designed and built is valid for monitoring the kinetics of oxygen consumption with the simultaneous measurement of the spectrum in the visible and dissolved oxygen. The tightness tests corroborated that all the cells used simultaneously are airtight, keeping their interior totally isolated from the exterior, showing a variability between cells of less than 10%. The results of the repeatability tests showed that the same wine measured simultaneously in the different cuvettes showed the same results both in the measurement of the consumption kinetics and in the measurement of the spectrum in the visible. The application of the system developed for the study of red wines allowed to know the characteristics of the consumption kinetics, obtaining that all red wines were initially able to take up the same amounts of oxygen (Omax), with values of 174 hPa. However, the wines made with Tempranillo grapes showed higher oxygen consumption (∆Omax_min), 115 hPa, and lower residual oxygen values (Omin), 59 hPa compared to than those made with the Garnacha grapes with 84 y 88 hPa of Omin and ∆Omax_min, respectively. One of the main advantages of this equipment is the ability to record the changes produced in the spectrum as the wine consumes oxygen, thus, an increase in red tones (450 and 580 nm) was observed in all the wines studied. It was found that the wines made with the Garnacha grapes underwent increases in absorbance between 400 and 460 nm and between 610 and 670 nm as they consumed oxygen, indicating an increase in the compounds responsible for the purple and yellow hues. On the other hand, wines made with the Tempranillo grapes, as they consumed oxygen, showed a decrease in purple hues.