WINETECH Technical Yearbook 2019

required preventative actions. It is especially applicable for winemaking processes after alcoholic fermentation up to and during bottling. Sources of air contact and the consequential dissolving of oxygen into the wine must be limited. Actions like rackings, unnecessary ullages in containers, wine transfers, cold stabilisation, filtration and bottling are actions which require the necessary attention. During these actions oxygen uptakes from 0,5 to 8 mg/L oxygen can occur ( www.vinlab.com ). Depending on the temperature, the dissolved oxygen concentration of wines can vary from 6 to 9 g/L. The concentrations are higher at lower

temperatures. During the cold stabilisation of wine, air contact must consequently be limited to prevent potential oxygen uptake. The rate of oxidation reactions is however faster at higher temperatures. Sufficient sulphur dioxide protection is consequently necessary. This depends on the dissolved oxygen concentration, seeing that 4 mg/L molecular SO 2 is required to bind 1 mg/L oxygen. If wine is transferred between tanks or barrels it is exposed to potential oxygen uptake. Such actions must consequently be limited if possible. Suppliers’ prescriptions must be complied with to ensure that equipment operates optimally. Leaking hose

seals, loose pipe connections and sheet filters are potential sources of oxygen dissolution. During rackings all pipelines and receiving containers must be purged with inert gasses like nitrogen, argon or carbon dioxide in advance. Rackings must also be from the bottom valve of the delivery tank to the bottom of the receiving container. When wine is transferred, containers must be kept full to prevent an air space on the surface of the wine. If air space does occur, the surface must be covered with inert gas. During the cold stabilisation of wine, the potential uptake of oxygen is favoured as result of the lower temperature. Sufficient sulphur

dioxide concentrations must consequently be maintained and containers kept full

(Steiner, 2013). REFERENCES

Steiner, T.E., 2013. Strategies to manage dissolved oxygen. How to identify practices that prevent unwanted oxygen absorption in wine. Wines & Vines , August 2013. www. hanna i nst . com/ resources /wi ne/ ebooks/measur i ng-do- i n-wi ne-hanna- instruments.pdf . www.vinlab.com/dissolved-oxygen-and-free- SO 2 .