The third category contained potatoes where the dry matter decreased towards the center, but then increased again when approaching the other end of the potato, shown in Fig. 4c. This is believed to be the dry matter gradient from the stem end towards the bud end of the potato (longitudinal axis). The two different dry matter gradients shown in Fig. 4a and b were representative for most of the potatoes analyzed, and the results are in good compliance with the findings of Peiris and co-workers [26]. This relationship is also established by other authors [18, 21]. For some potatoes, however, peculiar and deviating results were obtained, which also was clear from the specific prediction errors obtained from the software. This might indicate that the shape of the potato was irregular and hence not allowing accurate prediction, or that the water gradient within the tuber may not be constant for all potatoes. Overall, the internal gradients and the corresponding interpretations serve as a strong indication that the NIR approach is feasible for internal dry matter content predictions.