Strategies to Manage Dissolved Oxygen

My previous two blogs, How to Prevent Premox in White Wines and Chemical Marker Sotolon Found in Premox Wines gave oxygen a bad name, but at certain points in the transition of must to wine, oxygen is necessary. I found a helpful article in Wines & Vines written by T.E. Steiner called Strategies to Manage Dissolved Oxygen.
Concentrations of oxygen in the initial must are in the range of 4-6 mg/L. This amount of oxygen is essential in the early stages of fermentation when the yeast is in the growth phase. In fact, yeast consume the majority of oxygen which, happily for winemakers, results in the fermentation of sugar to ethanol. The problem comes when there is no sulfur dioxide (SO₂) at this point because the following potential negative effects can also occur:

• Enzymatic oxidation
• Polyphenol oxidase (PPO) oxidizes certain phenolic molecules in juice and must, but not wine, to produce quinones
• Laccase from Botrytis cinera or bunch rot, is an enzyme that has a wide range of oxidative substrates and is more resistant to SO₂
• Chemical oxidation
• The reaction of oxygen with certain phenols form quinones and hydrogen peroxide (H₂O₂), a stronger oxidizing agent that PPO.
• H₂O₂ also converts ethanol to acetaldehyde, resulting in a sherry-like aroma
The products that result from enzymatic and chemical oxidation reactions are summarized below:¹

• Microbial oxidation
• Acetic acid bacteria (AAB), Candida and Brettanomyces are dependent upon oxygen. In the presence of oxygen, AAB can produce acetic acid from ethanol as well as acetaldehyde and ethyl acetate.
• Certain "wild" yeasts belonging to the group Kloeckera and Hanseniaspora can be abundant in the must during the beginning states of fermentation and can produce high levels of acetic acid and ethyl acetate.²

The bottom line appears to be that if initial fermentation proceeds without sulfur dioxide, as many winemakers are inclined to do, then care must be taken so that the competing processes that can occur such as (1) enzymatic, (2) chemical and (3) microbial oxidation are kept in check.
References:
1. Jackson, Ronald S., Wine Science: Principles and Applications, Third Edition, Elsevier, Academic Press, 2008, pg. 298.
2. T.E. Steiner, Strategies to Manage Dissolved Oxygen, Wines & Vines, August, 2013.