Fouling factors are generally not applied in a plate heat exchanger design. The preferred method for plate heat exchangers is to design clean and add approximately 10% excess surface. Plate exchangers, which are properly designed with sufficient shear stress at the wall, will generally be fouling resistant. In applications where temperature sensitivity can cause degradation resulting in a fouling layer (e.g. scalding in starch containing food products), the excess surface added may be larger to lengthen the mean time between cleanings.