Dissolved oxygen in wine fermentation is an underrated subject.

You came to the right place to learn more about how it might happen AND how to understand what levels are okay.

To understand oxygen in wine, it’s fun to think about how fish breathe…

Yes, through their gills, but what are their gills really doing?

Well, if like me, you dozed off during science class then you’ll be fascinated to know that fish, just like all other animals, need oxygen to survive.

Their gills were developed to remove “dissolved oxygen” from water.

This is cool because we want to understand that oxygen does dissolve in water.

Oxygen actually dissolves readily in water and since wine is roughly 85% water, you can expect to find dissolved oxygen in your wine.

It’s important to know this because it has a massive impact on your winemaking. Of course, it all depends on how much contact is allowed between the wine and the air.

Why do we care about oxygen contacting our wine? Check out the previous post on why wine and oxygen don’t mix.

How to avoid excessive oxygen in your wine

Sulphur dioxide is your friend and can defend against oxygen dissolving and destroying your precious wine. If you are trying this at home, then note it takes 4x the sulfur dioxide for every molecule of oxygen.

It might be easier to understand with this equation:

2SO2 + O2 = 2SO3

This doesn’t mean that you can be lazy during the winemaking process and just remove all the oxygen at the end. Dissolved oxygen can actually coexist with sulphur dioxide in wine, it is not immediately removed, thus your wine is in danger for every minute that oxygen is allowed to persist. 

The moral of the story is to practice anaerobic winemaking by preventing contact with air using tools like “inert gases”. 

Dissolved oxygen is still underestimated and ignored more frequently than you would expect. Most of the time this is because of tradition. Wine has been made a certain way forever and it’s hard to change the old way of doing things. 

That said it is very important to know the oxygen levels in wine, as oxidation represents 7% of faults at wine competitions. It’s not something to neglect as you could end up with a vintage to forget.

Testing for too much dissolved oxygen in wine

This company has built a tool you can use to test dissolved oxygen and pH directly from your smartphone. I have not tried it yet myself, but it’s on the wish list!

Oxygen should be tested throughout the winemaking process, but a final test should be done before bottling. This test should have a result of 0.5mg/L or less. If it’s higher than that, then some work needs to be done!

Sparging – A solution to excess dissolved oxygen in wine

This is where Sparging comes in handy. Sparging is an amazing tool against too much dissolved oxygen and makes use of “inert” gases. If these are new friends to you, then here is a quick catch up.

How sparging works is that you inject fine bubbles of inert gas into the wine to remove oxygen. The bubbles move through the wine, pick up the volatile oxygen elements and carry them gracefully out of your wine.

An easy example of how this can be done is using Nitrogen. The Nitrogen gas picks up oxygen within the wine and then the oxygen exits the wine with the nitrogen.

The downside of this is that the Nitrogen will also pick up other volatile elements and usually these other elements are the ones that give your wine its beautiful flavor. So Sparge accordingly!

When nitrogen does remove these other volatile elements it also removes carbon dioxide, leaving your wine with a flat taste.

The better solution then is to “sparge” with a mixture of carbon dioxide and nitrogen to level out this effect. The result should be the same level of carbon dioxide and less dissolved oxygen.

If you have never bottled wine before, then this is something you’ll want to do one final test of before the wine goes into bottle.

Overtime wine can be exposed to air in a variety of ways, so it’s never safe to assume that wine tested a week ago is still the same as it is today. 

Many cellaring operations risk exposing the wine to air.

These operations could be pumping wine, filtering wine, racking wine, or even testing the wine. Oxygen is everywhere. Even wine that sits in a barrel for a year will easily add 20-40 mg/L of oxygen.

Measuring the dissolved oxygen in wine can be tricky because you may have to expose the wine to oxygen while you are testing it.

Thus any test results will be different now that the wine has been exposed to more oxygen.

Some people find that measuring the amount of oxygen that dissolves in wine during these operations is more easily done by measuring the decrease in free Sulpher Dioxide (SO2) after a “cellar operation” is complete.

This is effectively done by measuring the free Sulpher Dioxide before the cellar operation compared to the measurement of free SO2 a few days after the operation to indicate how much oxygen was picked up.

This was a bit more in-depth, but you are quickly becoming a pro! Feel free to leave questions below 🙂