What is the fine-grained topic of the following text: Tea sample (silver cloud dust) was extracted with water by traditional extraction method (TEM) at variable material: solvent ratio (1:20, 1:30, 1:40, 1:50), temperature (50, 60, 70, 80, 90˚C) and time (10, 20, 30, 40 mins). Only return the topic.
Traditional extraction method of tea sample