Robustness and variety independence are two key features in order to develop an industrial method for determination of dry matter content. The method used cannot be cultivar dependent or be affected by the skin color of the potato. A PCA analysis of average spectra from all on-line measurements is thus provided in Fig. 5. As can be seen, there seems to be a slight grouping along PC2. However, dry matter content and cultivar is slightly confounded, as shown in Table 1. Labeling the samples in the PCA plot with the corresponding values for dry matter content, reveals that the dry matter content is explaining the variation seen along PC2. This, rather than cultivar dependent differences, seems to be a more likely explanation for the slight grouping seen in Fig. 5. The PCA also indicates that the measurements are unaffected by the skin color. The two red colored cultivars (Asterix and Bruse) do not differ from the cultivars with yellow skin (Fakse, Folva, Mandelpotet, Saturna and Sava) along any of the two first PCs. This could also be related to the fact that the skin of the potatoes is only about 0.25 mm thick [19], and the interactance instrument sends light up to 20 mm into an unpeeled potato [4]. Hence, the skin should give an insignificant contribution to the spectra in this configuration. Noticeable differences due to flesh color was not seen, and is also unlikely, since all cultivars used had yellow or light yellow flesh color.