It is widely accepted that oak tannins can have a very significant influence on the tannic structure of wines. Besides their influence on mouthfeel, oak tannins are also antioxidants, and are viewed with renewed interest for their protective effect against wine oxidation. This hasn’t always been the case.  Measuring tannins contributed by oak barrels (or barrel alternatives) is a challenging task. Analysis methods have consistently failed to adequately measure these compounds in wines, preventing both researchers and winemakers from fully understanding and assessing their impact.

Why Do Oak Tannins Seem to Disappear in Wine?

Oak tannins are ellagitannins, relatively complex molecules containing ellagic acid as a main building block. Ellagitannins belong to a class of tannins known as hydrolysable, due to the fact that they easily degrade in acidic aqueous solutions, like wine. Degradation by oxidation is also a cause of their decline in wine. For a long time, it could be argued that levels remaining in wines, especially in red wines, were too low to have a real impact on mouthfeel.

More recently, it has been shown that oak tannins react with grape-derived wine phenolics, creating flavono-ellagitannins: a whole class of “hybrid” compounds containing both a grape derived flavonoid piece (either an anthocyanin or a flavanol), and an oak-derived piece. These compounds can be considered the “hidden” part of oak-derived tannins in wine. They evade detection by usual analysis methods, including HPLC, but play a determining role in enhancing color stability, modulating bitterness and astringency, as well as enhancing antioxidant properties.

They’re Hiding… but Can They Still Be Measured?

In the past few years, analysis methods based on releasing the ellagic acid building blocks of oak-derived tannins, followed by analysis by HPLC with UV detection, have been proposed. The lack of selectivity of UV detection can be an issue, however, especially when dealing with a matrix as complex as wine.

ETS has developed a method based on UHPLC coupled with triple quadrupole mass spectrometry (UHPLC-MS/MS QQQ). Accurate quantification is allowed by the use of an isotopic internal standard. This results in a selective and reproducible method that ETS now offers as a routine assay.

A wide field of possible applications:

The contribution of oak tannins is reported to vary significantly depending on oak species, with European pedunculate oak (Quercus robur) contributing the largest amounts, sessile oak (Q. petrea) moderate amounts, and American white oak (Q. alba) contributing less. 

Toast level can also have a strong influence, with heavier toasts decreasing the amounts of available ellagitannins. 

Responding to the recent regain of interest in ellagitannins, some coopers now offer barrels ranked according to their possible contribution to wine, from low to high.

Regardless of the forms of oak use, it is now possible for winemakers to assess their ellagitanin contribution to wine independently and objectively.

Take control of your wine’s structure, color stability, and antioxidant properties. Contact ETS Laboratories today to learn how our advanced analysis can help you optimize your oak aging process and elevate your winemaking decisions.

Gain the clarity you need to fine-tune your winemaking—Contact ETS Laboratories.