Saturday, August 16, 2008

Believing in something

A couple of years ago I asked a winemaker friend to explain to me the difference between tannin and tannic acid.

This friend is trained in microbiology and wine production, so I figured he would have a definitive answer. He did not. He said that he wasn’t sure about the relationship between tannic acid and tannin, because the words have often been applied and misapplied.

Well, I said to myself, that clears everything for me!

Being fairly well acquainted with cool climate wines, I am positive that their aging potential is seriously helped along by their acid make up, especially tartaric, which is the dominant acid of a few that are natural to grapes—and if you find that your dominant acid isn’t tartaric when you make wine, it’s usually best to add some.

Over time, the overall acidity (and tannin) in wine mellows as various reactions take place during the aging process, but it’s pretty well known that the tartaric portion of the wine’s structure plays a great role in fending off spoilage organisms, and that allows for the slow aging transformations.

For a long time, it was believed that tannins worked similarly to acidity as wine aged. Today, however, that belief is questioned and in fact, some question whether tannin is at all important in the wine aging process.

One of the results of being vocal or opinionated is that others will find you and take you to task. I was recently taken to task by a California winemaker because I posted on the Wine Lovers forum that acidity is what allows white wines to age and tannin is what allows red wines to age—the latter having more tannin and less acidity than the former.

I was spouting a long-standing belief, but the winemaker will have none of that. He wants to know which scientific study has proved that tannins help wines to age.

I did some checking around and I can’t help my winemaker friend by providing a study to support the role of tannins on wine aging. I can, however, report that there are scientific studies on the effects of tannin in nutrition and many other areas of plant and human health. One of those effects seems to be that tannins slow down oxidation.

Here’s my question to the winemaker: if tannins indeed do slow down oxidation, wouldn’t that help wine age?

Here’s my other question to the winemaker: what IS the difference between tannin and tannic acids?

The below links are interesting reading on this subject. Notice within some of the links that tannins can link to tannic acids through a process known as esterifying, and that those acids are not nearly as strong as tartaric or another grape acid, malic, or even as strong as citric acid.

My sense of the situation is this:

Forget the nonsense that white wines don’t age as well as red wines. That old saw is proven wrong on a regular basis with just Riesling alone, but with many other whites, all with high acid content.

Reds surely do have lower acidity and higher tannin content than whites, yet many of them age rather well. I believe that the anti-oxidant effects of tannin has an awful lot to do with the aging of red wines. But that is not to say that all tannin acts that way.
Hidden in one of the definitions of tannin I found that certain tannins, particularly from woods like oak, oxidize more easily than grape tannins.

Hmm. Could that be why some reds age longer than others?

Although winemaking is a science, understanding wine is quite often a belief system. Read the links below for the science; then, like the rest of us, form your own belief system. But please, don’t tell others that your belief system is THE answer.



TannicAcid 1



Copyright Thomas Pellechia
August 2008. All rights reserved.


  1. I'll take a stab at clarifying this ! Tannic acid is an "organic acid" because it contains hydrocarbons (= organic) and an acid functionality (something that can be ionized and release a proton (positively charged hydrogen ion). Organic acids by definition contain one or more carboxylic acids (R-COOH; where R represents the rest of the molecule) in their structure. By comparison tannins may or may not contain R-COOH groups, depending on how precisely the chemical is being described. The second key feature of many if not virtually all tannins and tannic acids is that they contain so-called phenolic groups which simply indicate that they have six-membered organic rings with one or more hydroxyl groups (R-OH) attached. The latter functionalities, esp. when two or more are adjacent in the same six-membered ring confer both antioxidative properties as well as prooxidative properties -- depending on the chemical environment at hand. There in lies an explanation as to how tannic acids and tannins can confer antioxidative properties in wine. The polyphenols are typically antioxidants until they encounter an oxidant such as the transition metal ferric iron, atmospheric dioxygen, free radicals, etc. At some point in time the solution's redox potential edges toward a more oxidative environment and the polyphenols become more oxidized, polymerize, and fall out of solution as a precipitate. During aging of wine, various organic acids including tartaric acid are also converted from their free acids (R-COOH) into the corresponding esters when they react with endogenous alcohols (e.g., ethanol = CH3CH2COOH) to form the fruity smelling/tasting (ethyl, etc.) esters. To a first approximation (big simplifying assumption omitting a zillion other chemical reactions) wine aging includes two key reactions: (i) formation of fruity esters (in addition to those already present) from organic acid precursors; (ii) a gradual shift from a reductive, polyphenolic-laden solution toward one that contains oxidized rearrangement products that eventually polymerize and fall out of solution. I need a drink...

  2. Thanks, Jay.

    Either it isn't taught that way in enology class or winemakers aren't listening. One winemaker swears that I am mistaken about those tannic acids.

    What's the esterification thing all about? I understand that alcohol serves to esterify tannic acids.

    I suppose that means that it helps them produce esters?

  3. Thomas said: "What's the esterification thing all about? I understand that alcohol serves to esterify tannic acids."

    Jay replies: One of the only high school chemistry lab sessions that had a lasting (memorable) impact on me was when a former Kodaker, Doc DeHollander had each pair of students synthesize particular esters from specific organic acids and alcohols. Doc D. had done his homework. As one went around smelling the end-products you'd swear you were smelling a variety of distinctive fruits. The general formula for an ester is R1-C-(double bond )O-R2 where R1 designates the rest of the organic acid precursor and R2 derives from the corresponding alcohol moiety. The following links give a fair overview:
    Under appropriate reaction conditions, virtually any organic acid may react with an alcohol to form an ester. Speaking from inexperience (my cellared wines are mere babes), I suspect that many aged wines might begin to converge toward a general flavor/aroma profile, mainly because a preponderance of particular esters derived from the main precursors (ethanol plus whatever organic acids predominate) could prevail. Dried fruits anyone?

  4. Thanks, Jay.

    Got me thinking. I'm no chemist (and I don't play one on the Internet or on TV!).

    Maybe you could be my blogchemist. Whenever I have a subject in mind that requires a chemistry get the idea, don't you?

    I'm still waiting to hear from the winemaker who says flat out that there are no such things as tannic acids and that I may be hallucinating from other acids.