Tannins - We’ve all heard the word, here’s what they are…

“Wow, this wine is tannic”!

“…lush plummy fruit supported by a fine tannic structure…”

We’ve all heard the sentence and the phrase just above, and as the title says, the word is thrown around like a Nerf football in a college stadium parking lot, but perhaps for that very reason, my instincts tell me that many wine drinkers, if really pressed for an answer, couldn’t define the term with any real precision. Let’s have a look…

Here’s a first surprising fact about tannins: tannins have no actual TASTE (and therefore no smell) at all. What we “taste” when we come into contact with tannins is these substances reacting with the proteins from which your mouth is made, and the sensation is purely textural. And indeed this is mostly what tannins bring to the table: “mouth feel”.

We know where tannins wind up, but what is their source? The answer is an easy one. Tannins are found in the skins, seeds, and stems of grape vines (as well as in tree bark, tea leaves, etc.). And because skins must be used to produce red wines, and because skins almost never wind up in the production of white wines, red wines are tannic and white wines are not. Tannins in fact are bound up with the substances called anthocyanins (the compounds that make red wine red) which are also found in the skins. And as this bundle (most properly called proanthocyanidins) comes into contact with the acids in the juice, the acids chemically split the tannins from the anthocyanins, allowing these coloring substances as well as the tannins themselves to completely pervade the wine.

But though skins and seeds and stems are the main source of tannins in most wines, tannins can also be introduced into a wine via…OAK! Tannins are present in wood as well, though these are not chemically the same sort of tannins that one finds in grapes skins, they are tannins nonetheless. What’s more, the tannins that leach into wines as they rest in oak barrels (new ones especially) are often “finer-grained” than those present in unaged wine. Interestingly, when red wine is aged in wood barrels, there is actually a tannin EXCHANGE between the barrel and the wine with the barrel giving up it’s finer wood tannins and then absorbing the coarser grape tannins back into its grain.

So tannins give red wines their texture, but they serve an equally if not even more important function. Tannins naturally retard oxidation, and what that means in the long and the short is that tannins allow wines to AGE. So at least theoretically, the more tannic a wine is, the longer it will hold, and/or the more gracefully it will age. But to be clear, not all tannins are created equal. The family of compounds to which tannins belong are very numerous and complex, so for example, tannins that ripen slowly as the berries come to maturity are chemically different than those that have been built via a one week heat wave. Additionally, we know that both Cabernet Sauvignon and Nebbiolo are tannic varieties, but those that have drunk a few examples of both know that the CHARACTER of the tannins in these two varieties are quite different.

Another way we can encounter tannins in wine is via what are chemically called tartrates. Tartrates are those little crystals that one sometimes finds clinging to the business end of a cork, or alternately, as the sediment that one might find in the bottom of a bottle of older wine. Now strictly speaking, tartrates are NOT tannins. Tartrates are actually a potassium salt of tartaric acid, but bound up with these salts, are often a certain percentage of tannins. Therefore, the more tartrates one finds in wine the further “evolved” a wine is, which reads as less tannic. Also for the sake of clarity (pardon the pun), not all sediments are either tartrates or percipitated tannins. In wines that are unfiltered, much of what is to be found in the bottom of a bottle of wine is quite literally tiny grape skin/pulp particles. These are easily distinguished from tartrates by their color. Grape sediment is purple and opaque, while tartrates are quite clearly colored CRYSTALS. And let’s just briefly take the opportunity to make it clear to everyone that ALL of these substances are NATURAL and HARMLESS. One should still avoid ingesting them because they are at least a distraction and sometimes can be quite bitter, but they are not in any way toxic. I cannot tell you how many times people have come back into the shop claiming that a bottle was bad, and the problem to which they were referring was normal sediment…this is when these folks get the abridged version of this piece, as well as a word or two about decanting…

The final view of tannins that we’re going to take was alluded to just above, and that process is called FINING. Fining is a sort of alternate mechanical filtration process that is NOT filtering. Filtering in wine is just what it is in any other pursuit - using a sort of screen to not permit particles larger than X to pass through. Fining is done via a neutral, flavorless substance that is added to a wine that is later racked off or filtered out. The most common substances used in fining are eggs whites (no, this is not a technical term - actual egg whites) or a subtance called bentonite which a dry powdered clay that expands when mixed with water. These substances are very effective at pulling down colloidal substances like tannins, pigmented tannins, and stray proteins that winemakers may want to eliminate.

So that’s the primer on tannins in wine. There is SO much more to the chemistry of these complex compounds, but that’s well beyond this layman, but suffice it to say that tannins are absolutely inseparable from a wine’s character as well as it’s drinking future. Without tannins, wine is not “wine”.

TOM CIOCCO