This document specifies a method for the detection of foods containing cellulose which have been treated with ionizing radiation, by analysing the electron spin resonance (ESR) spectrum, also called electron paramagnetic resonance (EPR) spectrum, of the food, see [1] to [13]. Interlaboratory studies have been successfully carried out with pistachio nut shells, [14] to [18], paprika powder [19] and [20] and fresh strawberries [21]. However, it has been shown that false-positive results can appear when analysing bleached nuts. For further information, see Clause 7 on limitations.