Noobie Question: What does "Volatile Acidity" taste like or do to a wine?

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?

Sooner or later one of the people who really understand wine chemistry will answer. Until then....

Most wines I think contain volatile acids. If they reach a point where they are noticable, people start talking about VA (or terms like "lifted nose"). Some people hate any trace of VA. Other think a little enlivens a wine- pretty standard in old style Rioja for instance.

I like a little VA myself. But when it becomes too much, it reminds me of airplane glue or nail polish remover. And I really can't stand that. I find the amount of VA varies in Musar even within a vintage, but it is frequently past my threshold and is the primary reason I'll gladly taste Musar, but seldom buy it.

[Robin Garr]

Dale's explanation is good. Here's a somewhat longer and more boring take on it from a <i>Wine Advisor</i> article a while back:

Volatile or vinegar?

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?

Put simply, volatile acidity is an attack of aceto-bacteria making acetic acid in an oxidative environment. It's the progression to vinegar, but uncontrolled it can lead to major problems.

Generally, it smells, well, volatile--shoots right up your nose and burns. As the bacteria does its work, the smell will go through stages, one of the more powerful is of nail polish or varnish.

Its taste is vinegar-like or, I suppose, varnish-like.

In the U.S. the feds allow a certain threshold level of v.a. in wine, after which the product has to be sent to the vinegar factory. Unfortunately, the feds only control what goes into the bottle...reasonably slight v.a. going in can come out worse when you pop the cork, especially if the wine isn't handled too well at the winery.

[Robin Garr]

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.

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.

Robin,

As I remember, ethyl acetate is formed by the combination of acetic acid and ethanol; you can't have the acetate without the acetic.

That's what I meant when I referred to acetic acid left uncontrolled will go through stages. I guess that wasn't exactly descriptive. IShouldabeen more clear!

"Volatile acidity" is a techno-wine chemistry term that refers to various acidic compounds in wine that evaporate rather readily (hence "volatile") as opposed to other acids that stay in solution and don't evaporate off (also known as "fixed acidity").

Malic, tartaric, and lactic acids are examples of "fixed acidity". They may crystallize out (forming the white crystals or granules you sometimes find in wine), and you may be able to smell them a bit (malic acid has a tart-apples aroma), but they don't readily evaporate or fizz out.

On the other hand you have the volatile wine acids, which evaporate readily:

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.

Acetic acid (CH3COOH) is the acid of vinegar, with its characteristic flavor and aroma. Except perhaps in the tiniest quantities, this is an unwelcome fault in wine.

Acetone, acetoacetate, hydroxybutyrate, and related compounds (sorry, couldn't be bothered to look up the chemical formulae). Aromas of nail polish. Port seems particularly prone to this, in my experience. It is a major fault in the 1977 Ports, particularly Graham's.

Butyric acid and friends (CH3CH3CH3COOH). Aromas of rancid butter or worse. An indication that things have gone really seriously wrong.

In small quantities, these may be just aromatic nuances (nuisances?). In larger quantities, they may blow off (evaporate harmlessly) with decanting or aerating in the glass. When obvious and obtrusive, they are distinct wine faults, and symptomatic of something that's gone wrong in either the winemaking or the ageing process.

-Paul W.

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.

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.

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.

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).

Thank God mercaptans rarely find their way into bottled wines (although you sometimes find them in barrel samples).

-Paul W.

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).

I've heard people say that with all the precautions now taken about excluding oxygen during elevage there are quite a few seriously reduced wines being bottled. And wouldn't you say that the well-documented "bottle stink" of older wines is often a mercaptan smell?

Mark Lipton
Oenochemist

Dear Oenochemist,
I think my brain just exploded.
'Winger

Dear Oenochemist,
I think my brain just exploded.
'Winger

Yeah, that is all pretty impressive. I use ethyl acetate in my butterfly collecting when I want some samples. Knocks them out fast.

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

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

Victor,
If you're talking about the production of acetic acid then, yes, oxygen is absolutely necessary for acetobacter to do its magic. Not all bacteria need oxygen, though, and many can't survive for long in its presence. In fact, oxygen is one of nature's best disinfectants. As for what governs the reactions, the oxidation of alcohol is carried out be enzymes related to alcohol dehydrogenase. And, yes, the cell count would have to get above a certain threshold for it to be a problem.

Mark Lipton

Thanks Mark.

Salute

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.

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.

Thanks Mark.

Salute

And Victor, acetic acid is a tiny piece of the by-products of yeast fermentation.

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

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

I agree about the CO2, but I don't think splashing is necessary, not routinely. As you say, in storage, the slight CO2 levels dissipate and even a tender transfer releases CO2 in the process.

The problem with retained CO2 these days may lie in the uber-control over protection against oxygen, which likely causes more than the natural CO2 retention. I hate CO2 in what is supposed to be still wine, especially when the wine is red.

On the bright side, the CO2 will (should) prevent acetic acid from progressing much...

On the bright side, the CO2 will (should) prevent acetic acid from progressing much...

No pun intended?

Mark Lipton

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.

I admit I am surprised by the number of California Pinots that show CO2, the wines having presumably been aged in wood at some point (the better ones, anyway), but I am particularly referring to all-stainless whites from eg Italy, Spain, where a hint of CO2 is part of the style, absolutely intentional and in no way a defect. I think it adds freshness to the mouthfeel of the wine.

On the bright side, the CO2 will (should) prevent acetic acid from progressing much...

No pun intended?

Mark Lipton

Well, now that you mention it...

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

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

That reaction is faster at lower pH. It's an acid-catalyzed process, so at lower pH you've got more acid to catalyze it. Trivia note: Organic chemists grace this reaction with a name (Fischer esterification). It's named after its purported discoverer, the legendary organic chemist Emil Fischer, who not only was a Nobel laureate but also gave the world the structures of the monosaccharides, the term "peptide" and the first explanation of enzymatic activity. Supposedly, he once got into a disagreement with Kaiser Wilhelm III, whereupon the Kaiser said "Ich bin der Kaiser" and Fischer supposedly retorted "Ich bin der Fischer." Alas, he died of cancer induced from many years of tasting every molecule he made.

Mark Lipton