Wine Tannins Unwrapped Via Clark Smith

International wine expert, Clark Smith noted that wine tannins are often confusing to winemakers, and gave a brief overview to explain some grape and wine tannin basics.
Wine Tannins Unwrapped Via Clark Smith - Articles


Clark presented a list of terms and definitions associated with grape and wine tannins and how they interact in wine. This information is summarized in the following table:

Compound NameDefinition
Phenol (Phenolic)Any compound containing a benzene ring with an -OH (hydroxyl) functional group attached.
FlavonoidAny class of three-ringed phenolics extractable from [grape] skins.
AnthocyaninAny of the five red-colored flavonoid monomers.
Flavilium IonLow pH red-colored form of an anthocyanin.
Anthocyanin MonomersSubjective to bisulfite bleaching. This form of anthocyanins is also capable of structural improvement. They are also vulnerable to oxidation.
MonomerA discrete small molecule which can serve as the building block for a macromolecule (polymer).
PolymerA macromolecule created by linking monomers together.
TanninA polyphenol with an affinity for protein.
Polymeric PigmentStable, unbleachable color which is the basis for refined texture.

Phenols (monomer units) can bond together to polymerize and form poly-phenols, or long-chained phenol units linked together. These poly-phenols can strip the proteins from saliva and give an individual a grainy feeling in the palate that is commonly described as the sensory perception of "astringency."

Polymers can form into linear and non-linear chemical formations. Linear polymerization is referred to as the non-oxidative polymerization of phenol monomers. Oxidative polymerization, on the other hand, forms daisy-chain, crooked chains of phenol monomers. Oxidative polymers tend to interact more strongly with salivary protein because they are not as compact as linear poly-phenols.

It is important to note that anthocyanins act as "end units" for poly-phenol chains during the polymerization process. This means that anthocyanins stop the polymer structure from polymerizing, or building, further. This anthocyanin bonding also inhibits daisy-chaining.

The sensory perception described as "bitterness," in contrast, is not generally related to polymeric formation of phenol monomers. Instead, bitterness is related to the concentration of monomeric phenols in the wine. The bitterness sensation is believed to exist due to the fact that phenols are not as soluble in wine.

Fining agents are traditionally used to chemically alter wine. Some of these chemical alterations may include manipulating the tannin profile of wine. The following is a brief table that emphasizes when to use certain fining agents in wine, and how they relate to monomeric (bitter) and oxidative-polymeric (astringent) phenols.

Fining AgentSourceReason to Use...
GelatinBones/Meat ProductsPolyphenol Astringency (Make sure you fine for astringency early. Fine for bitterness later on in production.)
CaseinMilkPolyphenol Astringency
AlbuminEggsPolyphenol Astringency
IsinglassFish BladderPolyphenol Astringency
Yeast BioleesYeastBring in softness.
PVPP--Monomeric Phenol Bitterness (Fine for it late if the bitterness is going to persist; don't fine red wine early because you'll take out anthocyanins.)

Clark emphasized the important role that phenolics play in red wine production. As anthocyanins will minimize the oxidative polymerization of phenols, having a high concentration of free anthocyanins should, theoretically, minimize the harsh astringency associated with red wines. Considering this theory, a juice produced with poor color (i.e., low anthocyanin concentration) will have increased perceived astringency. A darker juice (i.e., rich in anthocyanin concentration) should encourage shorter-chained polymer formation during fermentation and, therefore, produce softer red wines with less dryness or astringency.

Micro-oxygenation, which is commonly abbreviated to micro-ox, can contribute to red wine color stability and phenolic polymerization. Micro-ox is the direct and controlled application of oxygen into the wine.

Clark recommended the application of micro-ox at three phases of the winemaking process, depending on the goals of the winemaker:

  • Phase 1 (Color Stability Phase): Occurs post alcoholic fermentation and pre-sulfur dioxide treatment with an application of about 10 - 100 mL/L per month for about a month.
  • Phase 2 (Structuring Refinement Phase): Occurs post-sulfur dioxide treatment and pre-barrel aging with an application rate of 2 - 10 mL/L/month.
  • Phase 3 (Harmonization Phase): Occurs post-barrel aging at an application rate of 0.25 - 0.5 mL/L per month for maybe for a couple of months to soften the pithiness of the wine.