The invention relates to a method, a sensor unit and a machine for detecting “sugar end” defects in potatoes. The method comprises irradiating potatoes with at least one light source, for a plurality of locus points on each potato, wherein locus points lie on the end regions of the potato and other locus points lie in a central region of the potato. The light reflected from and/or transmitted through the respective locus points is selectively projected onto at least one photo sensor which generates light measurement signals for each locus point from the received light. At least one classification feature is determined from the light measurement signals. If at least one classification feature corresponds to a predefined “sugar end” criterion the respective potato is classified as having “sugar end” defects.