Penn State University researchers report that they have developed a new way to “fingerprint” the tannins that come from oak barrels and grapes, helping identify which compounds shape wine’s flavour, mouthfeel, bitterness, astringency and colour stability during ageing. The study used mass spectrometry and machine learning to analyse these complex tannin mixtures without first breaking them down in ways that can damage them, and it focused especially on hydrolysable tannins transferred from oak into wine. By testing wines and oak chip products, the team found that French oak had the highest levels of key tannins, followed by Hungarian and then American oak, and they also showed that barrel toasting alters these compounds, softening harsher tannins and producing more complex flavour effects.