Abstract: A method for producing biogas in an anaerobic digestion chamber from an un-treated organic substrate, wherein said un-treated organic substrate has a dry matter of content of in the range of 20 to 90% of total solids, wherein the method comprises the steps of, pre-treatment of the un-treated organic substrate, to form a slurry having a dry matter content of in the range of 8 to 19.9% of total solids, feeding said slurry to a digestion chamber; digesting said slurry in the digestion chamber to produce biogas and a digestate, wherein in said pre-treatment step a mixture of a dilution fluid and a liquid digestate from said digestion chamber is used to dilute the un-treated organic substrate.