In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, heterogeneous steel and a precursor to the modern Bessemer process that utilized partial decarbonization via repeated forging under a cold blast. By the 11th century, there was a large amount of deforestation in China due to the iron industry's demands for charcoal. By this time however, the Chinese had learned to use bituminous coke to replace charcoal, and with this switch in resources many acres of prime timberland in China were spared.