Sunday, April 22, 2012

"OXIDIZED WINES". Sometimes things are not what they seem...

After tasting an old wine from Argentina for "#MalbecDay" (picture), an interesting discussion developed this week on twitter: Oxidized wines.

Apparently, some people seem to be troubled by the fact that a wine is named "oxidized", while others seem to have problems to appreciate a wine that, as a sensorial perception, seems to be oxidized.

According to Jamie Goode ( "It's not easy to define when a wine is oxidized to the point of faultiness and when it is showing signs of oxidation consistent with normal aging. Except in extreme circumstances, this decision is not always clear-cut".

I agree with Jamie. There are more shades of grey when it comes to wine oxidation than many people (who think they know all about wine) care to admit.

Let's try to understand why it is not "clear-cut" by stating the obvious: Wine contains ethanol => The oxidation of ethanol can produce volatile compounds (acetaldehyde being the most important volatile wine carbonyl). Well, acetaldehyde is a molecule that is highly reactive. It displays aromas and flavors of straw, roasted nuts, and apple-like.

It would be simple to describe a wine that shows these characteristics (straw, roasted nuts, and apple-like aromas and flavors) as "oxidized", but things are a little more complicated than this:

  • Acetaldehyde can be formed both chemically (by wine oxidation - chemical formation of acetaldehyde relies on exposure to oxygen), but it can also be formed biologically as Saccharomyces cerevisae (most used commercial yeast) excrete acetaldehyde during the initial phases of alcoholic fermentation.
  • The odor threshold for acetaldehyde varies considerably (0.5 mg/L - 10 mg/L).
  • The addition of SO2 to stop alcoholic fermentation (as in the production of wines with residual sugar) leads to the formation of acetaldehyde.
  • Unless wines are handled carelessly (or, on purpose oxidized, such as in the production of Sherry or Madeira wines) after alcoholic fermentation, most of the acetaldehyde found in wine actually comes from yeast activity.

Some important conclusions can be drawn from these facts:

  • A wine can be perceived as oxidized by a sensitive taster to acetaldehyde, while another taster doesn't have that same impression. The difference in threshold might be as high as 20-fold!
  • A wine cannot be branded "oxidized" by the simple fact that acetaldehyde is perceived in the wine. The production of this volatile compound may have had a biological formation (and nothing to do with excessive exposure to oxygen).
  • If you are ever asked this question "You don't know oxidized wine when you taste it?", your answer should be: "No, I don't. I can't know if a wine is oxidized when I taste it (one hundred percent of the time), because the tell-tale aromas and flavors of acetaldehyde (green-grass, apple-like, nutty) may not have been caused by oxidation at all. Simple logic.

This is what Patrick Farrell MW (my mentor) had to say about it:

"One can form many different oxidation compounds, acetaldehyde being just one, either through exposure to oxygen or via microbial action, often the two in combination. The exposure can be accidental or purposeful. I pick up a walnut note on the finish of microx wines. Flavor compounds oxidize as well, some for the better and others for the worse.

Now, there’s oxidation in the bottle. Here’s where things get tricky. Sometimes, it is from dissolved oxygen in the bottle, other times insufficient SO2, and sometimes the combo. It is possible for a wine to oxidize in the bottle, without exposure to oxygen. Keep this in mind in that oxidation as a chemical term is different from oxidation as a wine term. Oxidation reactions involve electron transfer and do not require oxygen. So, it is possible to have a well stored bottle of wine, often white, that tastes oxidized, yet the closure has been fine."

I hope this helps you to understand a little better "oxidized wines". Sometimes things are not what they seem...

Luiz Alberto
  • >>> Master of Wine candidate
  • >>> Member of the Circle of Wine Writers
  • >>> Italian Wine Ambassador
  • >>> I combine my passion for wine with social media
 my precious… :)

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