Wine Oxidation and Acetaldehyde Management

[Raptor99]

I have had some problems recently with some of my wines developing a harsh flavor due to oxidation. Today I took a bottle of cheap grocery store sauvingon blanc out of the fridge to use for cooking. It had been opened and in the fridge for 2-3 weeks, so I tasted it to see if it was still good enough for cooking. To my surprise, it did not taste oxidized at all. With both my own wines as well as commercial wines, I have found that some taste oxidized 24 hours after opening, while others last several days in the fridge without a significant oxidation flavor. Why?

Apparently different wines have different anti-oxidant potential. Part of that is the level of free SO2, but I suspect that other antioxidants such as tannins and polyphenols also play a role. So I decided to do a little digging, and discovered a few things that I found quite interesting:'

• Ethanol oxidizes to produce acetaldehyde, which is the cause for the slow burn at the back of the throat.
• Yeast naturally produced acetaldehyde in the exponential growth phase, and uses some of that to produce ethanol in later stages. Under proper conditions, most of it is converted to ethanol before the end of fermentation.
• Sur Lie produces a reductive environment, which can decrease the amount of acetaldehyde: https://real.mtak.hu/49702/1/066.2017.46.1.14.pdf In this article, it is apparent that 60 days of sur lie can significantly reduce levels of acetaldehyde, even with 0 free SO2.
• MLF bacteria can also reduce the level of acetaldehyde: https://admin.lallemandwine.com/wp-content/uploads/2013/07/WE5-USA.pdf

This opens up some new ideas for me to contemplate. I will continue to dig into this, but wanted to share the two great links above. Enjoy!

 

[Rice_Guy]

Good info;
The fridge will not stop oxidation, the general rule in chem was reaction rate doubles for every 10C.
There are a number of chemicals that can lose electrons, yes tannins but also the pigments in the grape. I like dark pigments the more I make wines. The general concept is that the liquid soup has a ReDox potential. Different molecules in a wine have different potentials and there is a cascade from most reactive to less reactive when oxygen is limited. (AKA micro oxidation and producing sherry flavors). We could measure our wines ReDox potential and make a prediction about shelf life. ,,, But once a molecule is oxidized we never get it back.

 

[Raptor99]

The general concept is that the liquid soup has a ReDox potential.

That is the term that I was looking for, "ReDox potential."

So if SO2 is more reactive than alcohol, pigments, and tannins, it would bind with oxygen first, right? That's how we preserve color and flavor in our wine.

 

[Rice_Guy]

So if SO2 is more reactive than alcohol, pigments, and tannins, it would bind with oxygen first, right?l.

Yes molecules have a sequence in which they react,,, WHEN oxygen or other electron donors are present.

, . . . BUT we can overwhelm the system by having a surplus of oxidizer. ex aging a year in an oak barrel or HDPE carboy limits oxidation so that favorable reactions happen, direct exposure to air will create off notes in a month.