3.2 Production of sterols from wood pulp/tall oil
Commercially grown coniferous trees (Pinus sp.) are the usual source of wood that is chemically digested in the so-called Kraft pulping process. In this alkaline process the wood chips are digested at pH 14 (hence the term "soap") for about 18 hours at 50°C to free the wood fibers. The soapy material (black liquor pulping soap) is then separated from the cellulose pulp.