Phenolic compound (polyphenol) belonging to the large group of flavonoids (plant dyes). It is found in plants such as various vegetables and fruits, chocolate, green tea, berry skins, stems and grape seeds, especially in red wine. For example, Merlot and Pinot Noir have a high proportion, while Syrah has a low proportion. Catechin plays an important role as a repellent against micro-organisms and is formed spontaneously as a defence reaction, for example in the case of powdery mildew. Such substances are called phytoalexins. Catechin contributes to the formation of tannins or is a component thereof. It is a tanning agent and has an astringent effect in wine. Above all, however, it is responsible for the bitter taste. The substance has an antioxidant effect and therefore also has a health-promoting, positive effect with regard to increased blood fats.