WINETECH Technical Yearbook 2019

CHARL THERON: Private consultant KEYWORDS: Oxygen, oxidation, dissolved oxygen, oxygen measurement. FEBRUARY 2019 THE IMPORTANCE OF OXYGEN CONTROL DURING BOTTLING AND THE MEASUREMENT OF DISSOLVED OXYGEN IN WINE

Bottling is the last stage where oxygen can be dissolved in wine, causing negative quality characteristics, before the wine reaches the consumer. The possibility of oxygen absorption in wine exists during each process of bottling. Seeing that bottling usually takes place at lower temperatures, the oxygen dissolution is also influenced. It is recommended that the dissolved oxygen in bottled wine is lower than 0,6 mg/L and 1,25 mg/L for white and rosé or red wines respectively. It is however best to be as low as possible. This implies that it must be 0,5 mg/L or lower prior to bottling ( www.hannainst.com ). During bottling the dissolved oxygen should not increase by more than 0,8 mg/L, but preferably not more than 0,2 mg/L for white wine and 0,5 mg/L

for red wine. If the necessary precautions are however not taken during bottling, the increase can be up to 4-5 mg/L. The dissolved oxygen in bottled wine originates from the dissolved oxygen in the wine, as well as the oxygen in the headspace after bottling. This is known as Total Package Oxygen or TPO. Unless a vacuum filling machine is used, up to 2.8 mg/L oxygen can occur in the headspace. After bottling the TPO concentration should be lower than 0,5-0,6 mg/L in white wines and 1,1-1,25 mg/L for red wines ( www.vinlab.com ). The potential dissolution of oxygen in the wine can especially occur during the transfer, filtration and filling of the wine and is determined by the headspace in the bottling tank, filler and bottle.

PHOTO 1. A benchtop oxygen meter.

When wine is transferred to the bottling tank, all pipe lines and the tank must be purged beforehand with an inert gas like argon, nitrogen or carbon dioxide. It is also desirable to fill the headspace of the bottling tank under a low counter pressure of inert gas. Although a carbon dioxide concentration of 300-600 mg/L will lend freshness to white and red wines, higher concentrations

can cause an unacceptable sparkle in the wine, because carbon dioxide is readily dissolved in wine. Too high carbon dioxide concentrations can also cause pressure in the bottle, which can lead to the popping of corks at a later stage. A mixture of nitrogen and carbon dioxide may consequently be more acceptable.