The present disclosure generally relates to a method for controlled pretreatment of lignocellulosic biomass. The method comprises the steps of: Pretreating (S10) a lignocellulosic biomass material in a pretreatment arrangement, the pretreating comprising impregnating (S10A) the lignocellulosic biomass with an SO2 feed in an impregnation vessel of the pretreatment arrangement; collecting (S20) a number of process parameters of the pretreatment, which process parameters include at least a feed parameter related to the total amount of lignocellulosic biomass input to the pretreatment arrangement, and a dry matter parameter related to the dry matter content of lignocellulosic biomass input to the pretreatment arrangement; and adjusting (S30) the SO2 feed in response to the process parameters.