Wine racking in the winery and the use of inerting gases

The O₂ uptake in the different winemaking processes is generally considered to be negative for the sensory characteristics of white and rosé wines. Wine racking is a critical point of O₂ uptake, as the large surface area of the wine exposed during this operation and the inability to maintain an effective inert gas blanket over it.

The objective was to study O₂ uptake during the racking of a model wine without using inert gases and to compare it with the purging of the destination tank with different inert gases. In addition, inert gases were also used to protect the wine in the racking tank by blanketing the wine. Finally, a full-scale inerting study was carried out in a commercial winery during the racking of a white wine to evaluate the effectiveness of the use of different inert gases. Tank ullage space oxygen (HSO) and wine dissolved oxygen (DO) were monitored in different points during the wine racking.

Purging an empty tank with different inert gases was effective being the CO₂:Ar (20:80) mixture clearly the most effective, requiring less gas volume to displace O₂. The opposite result was found with N₂ because it worked in dilution mode. Although from an economic viewpoint, the most recommendable gas was CO₂.

The level of protection of the racked wine and the headspace over the racked wine in the empty destination tank differed depending on the gas used and the thickness (% of the tank volume) of the blanket formed with each gas. Based on the results obtained, purging with 25% of the empty tank volume of each inert gas is recommended to protect racked wine in a good cost-benefit way. To keep the headspace of the racking tank inert, blanketing with 50% of tank volume of Ar, CO₂ or the mixture of both were sufficient. Applying different volumes of gas had little effect on the DO of the wine at the tank outlet.

Acknowledgements: This research has been funded by ITACyL through a collaboration agreement with the University of Valladolid and the Fundación del Parque Científico de la Universidad de Valladolid. This project has received funding from AEI and Ministry of Science and Innovation MICINN (RTC2019-007319-2 Oxiprestop Project). The authors would like to tank Carburos Metálicos (Air Products group) and IVG Colbachini S.p.A for their material Support.