As Tu also presented at the project seminar, its preparation was described in a recipe from a 1,600-year-old traditional Chinese herbal medicine text titled Emergency Prescriptions Kept Up One’s Sleeve. At first, it was ineffective because they extracted it with traditional boiling water. Tu discovered that a low-temperature extraction process could be used to isolate an effective antimalarial substance from the plant; Tu says she was influenced by the source, written in 340 by Ge Hong, which states that this herb should be steeped in cold water. This book instructed the reader to immerse a handful of qinghao in water, wring out the juice, and drink it all. Since hot water damages the active ingredient in the plant, she proposed a method using low temperature ether to extract the effective compound instead.
This section from Tu Youyou’s Wikipedia page is incredible: