How to improve the oxygenation of wine?
Some factors have a beneficial or detrimental effect on the solubility of oxygen in wine. It is important to know these parameters to assure a proper winemaking and a long life to wines
Oxygen is a very important element in enology, even if it is normally ignored or underestimated. As a matter of fact, oxygen is clearly pivotal in the alcoholic fermentation stage since it allows the multiplication of yeasts and, consequently, the fermentation rate. There are also some oxygen-related practices, such as the hyper-oxygenation for white wines, which is used to increment some enzymatic reactions and to induce the polymerization of some compounds in order to increment the stability of the final product. During the maturation stage of red wines another widespread practice is micro-oxygenation, employed to promote the wine structuration, the color stabilization and the removal of some herbaceous aromas in favor of reduction fragrances.
Great attention was paid in the last years to micro-oxygenation, starting from the widely accepted notion that the oxygen concentration in barrels is always very low, frequently below the level required for the proper maturation of wine (50 mg/l). Hence, a number of techniques for the micro-oxygenation have been developed in order to provide the wine for a controlled amount of oxygen. As a matter of fact, it is important to provide a quantity of oxygen which is still below the instantaneous consumption, in order to avoid the formation of the damaging dissolved oxygen. Up to now it was difficult to manage this technique, both for the intrinsic problems in controlling the process and because not all the factors involved in the micro-oxygenation were known.
A research work by Igor Chiciuc, of the University of Bordeaux, now describes the factors that have a beneficial or detrimental influence on the wine oxygenation, allowing a proper employing of the micro-oxygenation technique. The results are presented in the table below and deserve a deep examination.
The experimental procedure was designed to get a proper evaluation of the transfer capacity of soluble oxygen. This was done by considering the different parameters that can influence the saturating concentration of dissolved oxygen or the conventional volumetric transfer coefficient (kLa), which quantifies the oxygen transfer efficiency. The study demonstrated that the concentration of sugar in the must induces an increase in viscosity that leads to a significant decrease of kLa. Surprisingly, the study also showed that a very low quantity of ethanol in the liquid part (0.05% in volume) promotes the oxygen transfer. On the contrary, the presence of carbon dioxide dissolved in wine, which dilutes the oxygen in micro-bubbles, strongly reduced the oxygen transfer. The presence of antioxidant (SO2) or oxygen-consuming compounds (polyphenols) didn’t show any effect on the oxygen transfer efficiency. Finally, also the tank shape influenced micro-oxygenation: high and small-diameter tanks should be preferred.
Chiciuc, Igor; Farines, Vincent; Mietton-Peuchot, Martine; and Devatine, Audrey (2010) "Effect of Wine Properties and Operating Mode upon Mass Transfer in Micro-Oxygenation," International Journal of Food Engineering: Vol. 6: Iss. 6, Article 9.