The substance, which belongs to the phenols (polyphenols), was first isolated and identified in 1963 in knotweed plants (Polygonum cuspidatum). It is an antioxidant (oxidation inhibitor) and is present in plants and plant foods, especially in peanuts, raspberries, mulberries and also grapes. In the vine, resveratrol is formed in the leaves and skins of vines affected by downy mildew or botrytis, as well as under stress conditions such as UV light as a defensive reaction. It is a natural fungicide, so to speak. Such substances are also called phytoalexins. The resveratrol content in grapes or wines from cool and humid areas is much higher than in dry and warm areas. It is particularly present in the skins of dark grapes in more than five times the amount of light-coloured ones.