Dissolved oxygen is generally considered detrimental to wine quality, especially if introduced after fermentation, storage, or bottling. The presence of oxygen after primary fermentation and during the later stages of winemaking can enhance browning reactions, chemical and microbiological instability, and the formation of off-flavors such as acetaldehyde.

Sulfur dioxide (SO2) is added as a scavenger to the wine to prevent these oxidation reactions. Knowing the oxygen content in wine is important through the entire wine production process. Oxidation is a common fault in bottled wines. In the past, oxidation has accounted for up to 7% of the errors/exclusions at wine exhibitions and competitions.

With the 913 pH/DO meter and the 914 pH/DO/Conductometer, the oxygen content of wine can be determined quickly and easily directly on site.

Red wine and rosé wine are used as examples in this Application Note. The closed sample is shaken well before analysis. No further sample preparation is required.

914 pH/DO/Conductometer equipped with an O2-Lumitrode and conductivity sensor for the determination of dissolved oxygen in wine samples.
Figure 1. 914 pH/DO/Conductometer equipped with an O2-Lumitrode and conductivity sensor for the determination of dissolved oxygen in wine samples.

This analysis is carried out on a 914 pH/DO/Conductometer equipped with an O2-Lumitrode, which is calibrated with 100% and 0% air saturation.

The prepared sample is carefully opened and the O2-Lumitrode is placed into the solution. The measurement is started and the DO content is measured until the value is stable. During the measurement, the sensor is gently moved in the solution to reach equilibrium faster. Do not stir vigorously, as oxygen from the environment can be introduced into the sample. Afterwards, the sensor is removed and rinsed well with deionized water.

For the analyses in this study, stable results were obtained within approximately 20 seconds. The obtained absolute standard deviation is smaller than 0.1 mg/L.

Table 1. Content of dissolved oxygen in mg/L in red wine and rosé wine.
  DO content in mg/L, red wine (n = 6) DO content in mg/L, rosé wine (n = 4)
Mean 0.69 0.98
SD(abs) 0.027 0.02
SD(rel) / % 3.83 1.86

The dissolved oxygen content in wine can be assessed quickly by using a 914 pH/DO/Conductometer and the optical sensor O2-Lumitrode. Other dissolved gases such as CO2 show no influence on the measured value, as long as no air bubbles adhere to the O2-Lumitrode. An accurate measurement takes less than 30 seconds and the sensor is completely maintenance-free. No need to worry about the quality of your sensor: if the O2 cap needs to be replaced, the instrument will inform you.

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Metrohm AG

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