Moderators: Jenise, Robin Garr, David M. Bueker
Brian K Miller
Passionate Arboisphile
9340
Fri Aug 25, 2006 1:05 am
Northern California
Dale Williams
Compassionate Connoisseur
11757
Tue Mar 21, 2006 4:32 pm
Dobbs Ferry, NY (NYC metro)
Brian K Miller wrote:reading a Cellar Tracker note for Musar, the critic noted "Volatile Acidity" as a problem. Given that I usually have been drinking younger wines, how would one describe VA and its impact on a wine?
Thomas wrote:bacteria making acetic acid in an oxidative environment.
Robin Garr wrote:Thomas wrote:bacteria making acetic acid in an oxidative environment.
Make that acetic acid, ethyl acetate or a combination. Acetic acid does the vinegar thing, ethyl acetate the varnish/nail polish/airplane glue thing. In my experience, I find ethyl acetate much more common than vinegar in modern commercial wines, although I've judged some home wines that were right up there in the vinegar department.
Paul Winalski
Wok Wielder
8872
Wed Mar 22, 2006 9:16 pm
Merrimack, New Hampshire
Oliver McCrum
Wine guru
1076
Wed Mar 22, 2006 1:08 am
Oakland, CA; Cigliè, Piedmont
Paul Winalski wrote:Carbonic acid (H2CO3), which readily bubbles off as free CO2. This is the "spritz" of young German wine and the bubbles of Champagne and other sparkling wine. In sparkling wine it's a positive feature. It's acceptable in young German wine, too. Elsewhere either fizziness or a prickly sensation of CO2 on the palate is an indication that something's gone wrong and unwanted bacteria have been at work.
-Paul W.
Paul Winalski
Wok Wielder
8872
Wed Mar 22, 2006 9:16 pm
Merrimack, New Hampshire
Robin Garr wrote:Make that acetic acid, ethyl acetate or a combination. Acetic acid does the vinegar thing, ethyl acetate the varnish/nail polish/airplane glue thing. In my experience, I find ethyl acetate much more common than vinegar in modern commercial wines, although I've judged some home wines that were right up there in the vinegar department.
Paul Winalski wrote:Robin Garr wrote:
I think varnish/nail polish remover thing is acetone (CH3COCH3), more than ethyl acetate (CH3COOCH2CH3), which has a fruity, pear-like aroma. Chemically, one would expect acetic acid present as a fault in wine to over time spontaneously combine with the ethanol to form the ester ethyl acetate.
Actual nail polish remover is usually either methyl ethyl ketone (2-butanone) or methyl propionate (a congener of ethyl acetate). Acetone was sometimes used, but it's too volatile and evaporates too fast. MEK is just a higher boiling version of acetone. And why do you think that acetic acid and ethanol would spontaneously combine in wine to form ethyl acetate? It's an equilibrium reaction:
CH3COOH + CH3CH2OH <-- --> CH3COOCH2CH3 + H20
The equilibrium constant for this reaction is close to 1, so whether it favors reactants or products depends mostly on the relative concentrations of water and ethanol. Guess which predominates in wine?I've found acetone aromas present occasionally in Sauternes that have a volatile acid problem, and in Ports, both good (when present in only in trace amounts) and bad (where obnoxiously present).
Having worked around acetone, ethyl acetate and acetic acid for all of my adult life, I am thrilled to report that I have rarely, if ever, smelled the former two in a wine and only occasionally the latter. One confounding problem, though, is some people get an acetic acid smell from ethyl acetate (I know of one Professor of Chemistry who suffers that fate), apparently from hydrolysis in the nasal mucosa or something like that...Thank God mercaptans rarely find their way into bottled wines (although you sometimes find them in barrel samples).
Redwinger
Wine guru
4038
Wed Mar 22, 2006 2:36 pm
Way Down South In Indiana, USA
Redwinger wrote:Dear Oenochemist,
I think my brain just exploded.![]()
'Winger
Victorwine wrote:Question for Mark;
Do these chemical reactions depend on the presents of oxygen? It makes sense that too much exposure to air could contaminate a wine, acetic bacteria is everywhere (floating around in the air we breathe). For these organisms to survive and reproduce surely oxygen is needed. But what actually governs these chemical reactions? The living bacteria themselves or the enzymes which they posses? I would assume that for any micro-organism to be either beneficial or harmful to a given volume of wine a certain “cell-count” (or population) would have to be reached within that medium.
Salute
Howie Hart
The Hart of Buffalo
6389
Thu Mar 23, 2006 4:13 pm
Niagara Falls, NY
I agree Oliver. CO2 is produced during both normal and malo-lactic fermentation and can remain in the wine if nothing is done to remove it. "De-gassing" is how it's removed, either by violent stirring, splashing during racking operations or filtering. Wines that are handled gently - fining instead of filtering, gentle transfer methods, etc. can retain CO2. However, I don't find it appealing in most still wines.Oliver McCrum wrote:Paul Winalski wrote:Carbonic acid (H2CO3), which readily bubbles off as free CO2. This is the "spritz" of young German wine and the bubbles of Champagne and other sparkling wine. In sparkling wine it's a positive feature. It's acceptable in young German wine, too. Elsewhere either fizziness or a prickly sensation of CO2 on the palate is an indication that something's gone wrong and unwanted bacteria have been at work.
-Paul W.
Paul,
I don't think this is quite right; many unflawed white and red still wines have enough CO2 to create the prickly sensation. Many of the white wines I import do, for example, and a number of new world Pinots do.
Victorwine wrote:Thanks Mark.
Salute
Victorwine wrote:Absolutely Thomas!
BTW as for CO2 production in wine I agree with Oliver and Howie. As far as “de-gassing”, if the winemaker is patient enough and the wine is properly bulk-aged, especially in oak barrels, the wine will “naturally de-gas” itself. (Just leave an opened bottle of soda with its top slightly twisted on and leave it out on the counter and see how long it takes to become “flat”). Like Howie, I agree the first couple of “wine rackings” (wine transfers) should be performed with “splashing”. But with winemakers using much more “modern” techniques (reductive winemaking) it very likely to find “more” CO2 in wines.
Salute
Thomas wrote:Victorwine wrote:
On the bright side, the CO2 will (should) prevent acetic acid from progressing much...
Oliver McCrum
Wine guru
1076
Wed Mar 22, 2006 1:08 am
Oakland, CA; Cigliè, Piedmont
Victorwine wrote:BTW as for CO2 production in wine I agree with Oliver and Howie. As far as “de-gassing”, if the winemaker is patient enough and the wine is properly bulk-aged, especially in oak barrels, the wine will “naturally de-gas” itself.
Mark Lipton wrote:Thomas wrote:Victorwine wrote:
On the bright side, the CO2 will (should) prevent acetic acid from progressing much...
No pun intended?
Mark Lipton
Victorwine wrote:Another question for Mark or Thomas, (sorry gang)
CH3COOH + CH3CH2OH <-- --> CH3COOCH2CH3 + H20
For this reaction to be a real problem in wine doesn’t the pH have to be close to 4.7?
Salute
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