Colourless substance belonging to the phenols, which is embedded in the plant cell wall and thus causes lignification (lignification, lat. lignum = wood). It is also responsible for the so-called "yellowing" of paper. After cellulose, lignin is the second most common organic substance on earth. It is naturally also present in oak wood with a proportion of over 20% and plays an important role as a preliminary stage to aromatic substances. During the toasting of barrique barrels, lignin is broken down into aromatic aldehydes. The most important one is vanillin, which gets into the wine during the barrique ageing process. See also under Tannins.