This part of ISO 17225 determines the fuel quality classes and specifications of graded wood pellets for non-industrial and industrial use. This part of ISO 17225 covers only wood pellets produced from the following raw materials (see ISO 17225-1, Table 1): — 1.1 Forest, plantation and other virgin wood; — 1.2 By-products and residues from wood processing industry; — 1.3.1 Chemically untreated used wood. Thermally treated biomass pellets (e.g. torrefied pellets) are not included in the scope of this part of ISO 17225. Torrefaction is a mild pre-treatment of biomass at a temperature between 200 °C to 300 °C.