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Winemaking challenges

To reduce the oxidation risk in white and rosé wines, we must take a close interest in the actors of oxidation, namely polyphenols, and above all act as soon as possible. We tell you all about this.

Different strategies can be implemented in a practical way, in the cellar, to limit the wine oxidation. All consist in better managing the main players of the oxidation mechanisms, namely oxygen and polyphenols. Inerting, fining, oxygenation or the addition of antioxidants, whether in musts or wines, are examples. In the case of white and rosé wines, polyphenols management in the pre-fermentative phase is an essential lever for reducing oxidative risks. But for this, it is essential to qualify the juices, which means to know their polyphenol content. Indeed, the choices of treatments to be applied in the pre-fermentative phase must be adapted according to this richness.

Rapid and reliable analysis of polyphenols with Polyscan helps decision making

Within our Enology Team, we have been developing this expertise for 5 years with our decision support tool: the PolyScan. An analysis performed with the Polyscan provides the winemaker with various indices: the EasyOx index, which indicates the amount of easily oxidizable polyphenols in the sample; the PhenOx index which indicates the amount of total polyphenols. From pressing, the analysis allows monitoring the increase in the concentration of polyphenols extracted during the cycle and thus to optimize the separation of free-run and press juices.

Our work has enabled us to define expert rules that are displayed on the user’s screen to support him in his decision-making. For example, during white and rosé pressing, we were able to define with reliability the moment which corresponds to the optimal separation of the juices according to their polyphenol concentration, which means the moment when the quality of the juice changes from free-run juices, low in polyphenols, to press juices, rich in polyphenols. When this increase is detected by the analyzer, a message appears on the operator’s screen advising him to separate the juices.

In the settling tank, the indices allow to qualify the juices, which means to assess their richness and their composition in polyphenols. Thanks to the large number of measurements in the unique database associated with the device (more than 40,000), statistical studies have enabled us to determine in a robust manner the median values by grape variety of the must in the settling tank. These values are available to the user for direct on-screen comparison. This comparison allows a rapid diagnosis of the polyphenol content of the tank to adapt the pre-fermentative treatment of the must.

Choose the most suitable treatment according to the polyphenol content of the juices

If the juice is rich in total polyphenols, the risk of rapid oxidation of whites and rosés is greater. The winemaker’s priority is therefore to reduce the polyphenol content in the juices from the pre-fermentative stage, in the most efficient way possible and adapted to obtain the desired wine profile. These juices rich in polyphenols are those whose PhenOx value is greater than the median of the grape variety. Should we then proceed to fining or oxygenation? This is where the second indicator, EasyOx, comes in. If the EasyOx value is low or equal to the median, we recommend a must fining. If the EasyOx value is greater than the median value, the must oxygenation can be chosen because it will be effective in reducing the amounts of polyphenols, the enzymatic oxidation factors contributing to this index.

From a practical point of view, the must oxygenation aims to reduce the amount of total polyphenols to a level equivalent to that is observed in free-run juices. For this oxygenation operation, we have also implemented an expert rule, still based on all our data collected over the years, which tells the operator when to stop the oxygen supply in the juices.

The Polyscan, thanks to the various indexes provided and its expert rules, thus allows to help decision-making immediately in these stages of the process where every minute counts. By relying on the indicators and their changes during a process, the operator can adapt his winemaking strategy and manage his operations very finely. This is of crucial importance in the pre-fermentative stages, an essential lever in preventing the risk of oxidation in white and rosé wines.

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