The main objective of this paper is to present an experimentally validated methodology for a quasi steady-state heat and mass transfer numerical modelling of a complete steam–air industrial sized sterilisation process, including the loads being heated within the autoclave. The presented methodology was developed upon our previously published work of an empty autoclave [13], with the addition of packaged products and the trays in which the products sit inside the autoclave within the numerical model. The proposed methodology accounts for heat and mass transfer between the products and autoclave using assumption of a one-dimensional heat transfer within the products. Also included now in the model is an actual operational Proportional–Integral (P–I) controller. The model would be able to simulate a fully functional autoclave using vessel temperature profiles, initial and boundary conditions as inputs. Since the model was built and solved solely using commercially available software, Simulink® by MathWorks, it will be possible for an adaptation by manufacturers in the pharmaceutical and food processing industries as a tool to analyse current steam–air sterilisation processes within a factory environment. The detail break-down in thermal energy consumption during a sterilisation cycle allows for better engineering decision making when retro-fitting existing equipment in brown-field sites and for better process and autoclave designs in green-field plants.