Dissolved Oxygen (Do) is a measure of the amount of oxygen gas (O2) dissolved in solution in wort or beer, as opposed to the total amount of O2 in a sample, which includes that present in equilibrium with the dissolved O2, i.e., that present in the headspace. It is typically measured using an oxygen analyzer (oxygen electrode). The solubility of oxygen depends on temperature (gases are less soluble as the temperature is raised) and on the pressure of the gas over the liquid. Henry’s Law states that
p = partial pressure of gas (in this case oxygen)
kH = Henry’s constant, which depends on the gas, solvent, and temperature
c = concentration of gas in solution
Thus, the more gas that a liquid such as water, wort or beer is exposed to, the more will go into solution. Furthermore, separate gases will respond individually.
The concentration of gas dissolved also de-pends on the concentration of other materials in solution.
The dissolved oxygen content (abbreviated to dO2) is relevant from the perspective of fermentation control, it being necessary to provide yeast with the correct quantity of oxygen to satisfy its need to synthesize unsaturated fatty acids and sterols. dO2 is also important in terms of wort and beer stability, oxygen adversely impacting quality and performance by elevating color, cross-linking polymers (leading to reduced rates of wort separation), promoting haze, and causing flavor instability. For this reason, the measurement (and, if warranted, elimination) of dissolved oxygen is a critical element of quality assurance and control for breweries.