Micro-oxygenation During the Aging Process: When and Why?

Micro-oxygenation is an essential part of aging wines—in particular, red wines. It influences tannin structure, mouthfeel, aromatics, and color—in other words, pretty much all of the elements that give the wine its character. This essential process should be managed carefully and systematically by winemakers as they’re getting the wines ready for bottling, sale, and of course, drinking.

In winemaking terms, micro-oxygenation can mean a couple of different things. It can refer to the slow oxygen transfer that takes place when a wine is put into barrels for aging. Most of the time, however, it refers to a process that is more technological: the introduction, through a special device, of tiny air bubbles in a wine that is being fermented or aged in tanks.

Both use of barrels and more technological means of micro-oxygenation can achieve this necessary interaction between the wine and oxygen. But as Jason Diefenderfer of Hope Family Wines points out, these methods shouldn’t be approached the same way. “Micro-oxygenation is a misunderstood practice. It doesn’t just speed up the process that would occur when you’re using barrels. It’s a different process that makes a different wine. You shouldn’t think of it simply as a way to save money on barrels.”

For Diefenderfer, the choice of barrels or micro-ox is linked to whether the wine is meant for immediate consumption or cellaring; barrel-aging is used for wines meant for a longer life. For many winemakers, patience in aging a wine generally correlates with a certain patience before drinking it.

Calibrating Doses

One of the big differences between these two processes of oxygenating wine, of course, is control. A barrel’s oxygen transfer rate varies according to the thickness of the staves, the density of the wood, the age of the barrel, and how tightly the barrel is put together, but it’s not something that can be adjusted mechanically. On the other hand, micro-oxygenation in tanks can be calibrated so that the addition of oxygen in the fermenting must or the wine is precisely controlled.

Calibrating the oxygen input is crucially important here, especially when using it onMicroOx_Support a wine that has finished its fermentations. The goal is to round out the wines by improving the structure and aromas, but an excessive dose can have the opposite effect—something that’s tough to offset at this later stage in the winemaking process.

In the book Oxygène et vin (Oxygen and wine), published by micro-ox system company Parsec in 2008, enologist Mathieu de Basquiat described the effects of a controlled experiment where low, moderate, and high doses of oxygen (between 1 and 3 mg/L/month) were used on the same wine during aging. While the low dose increased complexity, tannin structure, and aromatic expression, the high dose wound up having the opposite effect, with drying tannins and aromas that seemed tired and past their prime. As the expression goes: Too much of a good thing is a bad thing.

It can certainly be tempting to overdo the treatment, especially when dealing with, say, a wine from a cooler vintage that shows harder tannins or a wine with a greater reductive tendency. However, the risk is winding up with a wine that shows lack of ripeness, tired aromatics, and drying tannins—not exactly an improvement.

To ensure that micro-oxygenation achieves its intended goals, it is important to take into account factors such as the presence of lees (or not), grape varieties present in the wine (which can be more oxidative or reductive, depending on the grapes and their growing conditions), level and composition of the pool of phenolics, and acidity and pH. Monitoring dissolved oxygen (DO) levels is also essential to make sure the wine is not accumulating oxygen (and thus suffering from oxidation, rather than just getting a bit of oxygenation); it’s important to taste the wine regularly to detect any sign of oxidative aromas or characters. The tools of micro-oxygenation are precise in terms of dosage, but it is critical for the winemakers to be precise as well if the desired effects are to be obtained.

Photo Credit: Total Wine

About the Author

Rémy Charest is a Quebec City-based journalist, writer, and translator. He has been writing about wine and food since 1997 in various Canadian and American print and online publications, includijng Le Devoir, Le Soleil, Coup de Pouce, EnRoute, Palate Press, Punch Drink, WineAlign and Châtelaine, and has been a regular radio columnist for Montreal's CJAD and CBC/Radio-Canada. He is additionally a wine judge for national and international wine competitions, notably the National Wine Awards of Canada and the World Wine Awards of Canada organized by WineAlign.

Rémy Charest Photo Credit: Jason Dziver


  1. Dear Remy, if I may add my grain of sand, I would say that it is of utmost importance, as well, to make sure all fermentescible sugars are exhausted. This means going beyond the usual check of RS < 2 g/L and actually check that the sum of glucose and fructose in no higher tan 0,5 g/L. Failure to do this has resulted in wonderful breeding grounds for Brettanomyces and some contamination bacteria, completely changing the flavour profile of once wonderful wines.

  2. An interesting input on an aspect I hadn’t looked into, Antonio. There’s always more to the story, insn’t there? Thanks for that input.

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