Question:
Why do people swirl wine?
Answer: Most of the enjoyment of wine comes primarily from aromas. Swirling the wine will aerate its aroma slightly, potentially releasing more. These will rest in the bowl of the glass as you raise it to your nose. For this reason, you do not need to constantly swirl a glass of wine (unless it needs heavy aeration), just enough to release aromas before your first sip.
How exactly does swirling work?
Swirling causes alcohol to evaporate which delivers the aroma compounds in wine to your nose.
Swirling helps release the hundreds of different aroma compounds found in wine. These compounds are the reason why wine has such an array of aromas. For example, in a rich, powerful California Cabernet, you might find blackberry, cedar and vanilla–all at the same time. These compounds are tiny, so small that they float on evaporating alcohol into our noses; this is what delivers the aromas of wine into the olfactory system. We say aroma because a large part of wine enjoyment is found in our nose’s ability to smell.
FACT: Aromas found in wine are called “stereoisomers” which are mirror-images to smells we are familiar with from our day-to-day lives (like blackberry, rose, butter, etc )
If you want to prove the importance of aroma in wine to yourself, just plug your nose. All the aromas of fruit will disappear and the true taste (i.e. sour, bitter, sweet, and salty) and texture of wine will remain in isolation from the aromas.
How does one swirl?
And not make a mess everywhere…
The easiest way to start swirling is to place your thumb and forefinger at the base of a stemmed wine glass while it’s siting on the table. Then, draw little circles on the table while gripping the base of the glass.
As you get better, you can try swirling without a table beneath your wine.
When you get really good, you’ll even swirl your coffee…
By Madeline Puckette, WineFolly
From: http://winefolly.com/tutorial/why-swirling-a-glass-of-wine-is-better/