Letting the Wine Breathe (Science of Aeration)

My experience with the first Bordeaux experiment got me thinking more about what happens to wine after it is poured out of the bottle.   Swirling, decanting, letting the wine breathe.  Turns out 2 things happen.  Evaporation and oxidation.

Evaporation is straight forward.  Volatile compounds disperse into the air. These compounds include alcohol, sulfites (S02), sulfides and ethanol.   The sulfites are put into wine as an antimicrobial and antioxidant to preserve the wine.  Sulfites may give a smokey, burnt matchstick aroma.  Sulfides, in larger concentrations, may give off a rotten egg smell but in lower concentrations will give a smokey or tar like odor. Ethanol, alcohol, will be present as well.  Not so nice in large concentrations but should air out fairly quickly.  From my experience with the Chateau , theses harsher aromas did give way to more pleasant ones.

Oxidations is simple to visualize.  It’s the same process that turns fruits, like apples, brown.  A simple explanation is oxygen interacts with polyphenols.  Another, more detailed answer is the tannins begin to soften and breakdown.  However, that’s not exactly true…and a whole lot can be written on what is happening to tannins.  Actually there are a ton of scientific papers on the subject.  Since I’m still a newbie and don’t want to fully geek out, I’ll keep it simple.

When most people say tannins, the are actually referring to a mixture components: condensed tannins (polyanthrocyanidins) and psuedo-tannins (catechins, epicatechins gallic acid).  Oxidation of these components generally take a long time..think of it as aging in the bottle (again another topic I can probably geek out about).  However, my first experiment only took a couple of hours.  So what happened??  There is probably  a slow interaction with oxygen and the psuedo-tannins.  These changes will lead to a less of a bitter taste or softening of the wine.

Letting the wine breathe is good for wines with a lot of tannins (and psuedo-tannins).  It’s not necessary for most white wines because white wines contain fewer tannins.

My takeaway, at least for the next 2 Bordeaux experiments, I should let the wines breathe before really drinking it.




Grape and Wine Color and Tannins, Bruce Zoecklein, Head, Enology-Grape Chemistry Group Virginia Tech , 2006

Recent Developments in Wine Oxidation Chemistry, Andrew L. Waterhouse Cornell University, September 13, 2011



Oxidation mechanisms occurring in wines,Carla Maria Oliveira a,b, António César Silva Ferreira b,c, Victor De Freitas d, Artur M. S. Silva a,

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