Recently, I came across an article on my wine feed titled, "Tannins from oak barrels that flavor wine are ‘fingerprinted’ by researchers" which peaked my interest.
It's been known that wine aged in oak barrels can contribute flavors described as coconut, vanilla, spice, caramel and smoke that can affect the taste and mouthfeel of wine. Tannins also come from grape skins and which tannin, grape skins or oak wood contributed to the specific wine flavor was something that remained difficult to quantify.
Recently, scientists at Penn State developed a way to chemically characterize and identify individual tannins in wine that come from oak barrels and contribute to its flavor profile.
The word "tannin" is usually mentioned when speaking about red wines. There are two major types of tannins, hydrolysable tannins (HTs) and condensed tannins (CTs) found in foods and beverages. There are two major types of HTs, the ellagitannins (ET) and gallotannins (GT).
Why are these tannins of especial interest in winemaking?
- HTs affect both chemical stability and sensory quality
- HTs are generally exogenous to wines, primarily introduced from oak and other wood species through barrel aging or the use of oak adjuncts such as chips
- HTs compounds enhance wine antioxidant capacity, stabilize anthocyanin pigments, and contribute to mouthfeel characteristics
- HTs have been described as imparting a smooth, velvety astringency
For the above reasons, HTs are essential for understanding wine composition and maturation, and a rapid measurement method is particularly valuable for achieving quick analytical turnaround in industry settings.
However, measuring and quantifying these HTs has traditionally been time consuming, but using in-source fragmentation (ISF) instead of acid-hydrolysis (AH) generated class-specific ions directly from all HT structures and retained the chromatographic profile of the native HTs.
Realizing the advantage of using ISF, the researchers aimed to do the following:
- (1) Introduce and validate a rapid, robust in-source fragmentation (ISF) method, called hydrolysable tannin fragmentation fingerprinting (H-TFF) for quantifying ellagitannins and gallotannins, using both quadrupole time-of-flight (QTOF) and triple quadrupole mass spectrometry (QQQ) platforms
- (2) Compare conventional acid hydrolysis (AH) methods with H-TFF for quantifying HTs across both QTOF and QQQ instruments
- (3) Characterize oak chip extracts prepared in both methanol and wine matrices using the H-TFF method, enabling compound class-level tannin profiling
- (4) Integrate H-TFF with an existing condensed tannin fragmentation fingerprinting (C-TFF) method to generate a comprehensive tannin composition fingerprint across a set of oak-treated wines
To validate their method, the team used cross-platform comparisons between QTOF and QQQ and comparison to AH, using 22 red and 20 white wines.
Their research involved a collaboration with Gallo, a California-based winery that provided some of the 22 red and 20 white wines analyzed in the study.
The team conducted experiments using 15 commercial oak chip products representing three types of oak used for wine-aging barrels, French oak, Hungarian oak and American oak and five toast levels.
After adding the various types of oak chips to wine samples, the researchers could then characterize the differences in hydrolysable tannins in those treated wines to determine if their method was consistent with linearity, limit of detection (LOD), accuracy, precision, and matrix interference.
The newly developed and validated H-TFF method was first applied to these 15 oak chip samples extracted in 200-proof ethanol to quantify the ET and GT in these extracts.
Red base wine (RB) and white base wine (WB) with minimal oak addition were used for calibration curve dilutions and method validation of the H-TFF.
Quantification was performed using the calibration curves prepared in a methanol-based model solution to minimize matrix effects and improve accuracy. The results revealed that, regardless of toast level, French oak contained the highest concentrations of both ellagitannins and gallotannins, followed by Hungarian oak and American oak .
In summary, the researchers found that H-TFF enables the rapid, non-destructive analysis of ellagitannins and gallotannins, offering a practical alternative to conventional AH.
References:
1. Penn State,
Tannins from oak barrels that flavor wine are ‘fingerprinted’ by researcher.
2. Yanxin Lin, Bruce S. Pan, Robert (Qiang) Siu, and Misha T. Kwasniewski, "High-throughput fingerprinting of hydrolysable tannins in wine and oak wood using in-source fragmentation on QTOF and QQQ platforms",
Food Chemistry, Volume 507, 1 April 2026, 148170.
