Oliver White wrote:

> Chemistry actually backs up a lot of the claims of wine tasters. For
> instance, a Chardonnay can be characterised as "Buttery". Sounds
> bizzare, but a certain kind of yeast produce in fermentation the same
> chemical as found in butter flavoring for popcorn!

Diacetyl (butter flavor) is produced during malolactic fermentation,
which is done by bacteria, not yeast.

>
> In my school days, one of my favorite experiments was creating
> "esters". From a bunch of strange chemicals, including Sulfuric Acid
> and certain alcahols we produced the smell of banana (well more like
> banana flavored lollies or milk).

Yup, I loved that experiment, too, but preferred the pineapple ester.


> When different kinds of grape are fermented, different acids can bond
> with alcahol, producing different smells. The longer wine is stored in
> the bottle, the more of these chemicals are produced, and the primary
> fruit flavors that you might find actually eating the grapes
> themselves tend to fade.

Hmmm... This seems a bit simplistic to me. The primary fruit flavors
are low molecular weight esters that might very well diffuse out of the
wine slowly over the years. New esters are almost certainly produced as
you describe it, but what acids might be involved I cannot guess.

>
> An aged wine might take on the smell of leather... just speculating
> here, but an ester produced from tannic acid and alcahol might
> actually fit the bill.

Doubtful. The other major classes of odorants in wine are
sulfur-containing molecules (sulfides and thiols). Many of the
"tertiary" aromas are the result of these sorts of molecules, giving
rise to suggestions of mushrooms, tar, earth, leather and truffles.
FWIW, many of these same odorants would be unpleasant if present in
higher quantities (many people actually *like* eau de skunk at very low
levels).

>
> I guess in a sense the winemakers do put these smells in. By
> extracting more tannins from the skins when they crush the grapes,
> they might find that in years to come, certain flavors and smells will
> be created. Generations of experience go into these sort of
> formulations.
>
> Esters are just one kind of chemical you might find in wine. I'm sure
> there are plenty of references out there for those who are interested.