Resveratrol is found in the skins and seeds of grapes, as well as in blueberries, mulberries, cranberries and peanuts, and in the roots of Japanese knotweed. While early resveratrol supplements were produced from grape skins, most products sold today are made from the more economical, and more concentrated, Japanese knotweed (Polygonum cuspidatum).

This plant is also known in Japan as kojo-kon, and in China as Hu Zhang. Some supplements contain added red wine extracts, both for their resveratrol content and for marketing purposes.In the typical extraction process, Japanese knotweed roots are sliced before being heated up in large metal chambers known as extractors. The plants are first tested to prevent contamination with heavy metals or chemicals.

To seoerate the resvertarol from the plant tiossues ethanol or methanol is used a solvent, which results a crude liquid extraction. The resveratrol extract is then processed by running them over a coulumn of silica under high pressure or by various methods. It is then vaccum-dried to remove the solvent, this then helps to produce resveratrol powders. Resveratrol powder is combined with fillers such as rice flour or hydroxypropylcellulose to manufacture pills and capsules.

When grapes are used to make resveratrol, the production process is similar to that described above. Alcohol is used to dissolve the resveratrol contained in the skins or seeds, and the resulting liquid is refined further and dried. Because of the low relative content of resveratrol in grapes, supplements made exclusively from grapes are very expensive to produce.

Scientists at the University of Alicante in Spain have now developed a biological method of producing high-quality resveratrol from grapevine cells. This method is cheaper and more reliable than traditional extraction from grapes. The perceived higher value of grape-based supplements could make this a viable alternative to grapes as a source of premium-grade resveratrol.