Standing in front of the potato shelf at the supermarket, most consumers expect a perfect picture: clean, smooth, and flawless tubers. Food retailers set extremely high standards for the external quality of washed table potatoes, especially for small-pack formats. But how exactly is it decided which potato is "good enough" for sale? Here is a look at the criteria, metrics, and defect types used in potato quality assessment.
1. The Basic Criteria: What Makes a Good Table Potato?
Before optical sorting even begins, basic agronomic and culinary requirements must be met. As Diepenbrock et al. (2016) explain in their overview, taste and cooking properties are the primary focus for table potatoes, largely determined by variety selection and fertilisation (P and K). Also critical are uniform size and shape (sorting typically >30 mm), good peelability through shallow eye depth, and the strict absence of greening and scab.
The international basis for marketing is the UNECE Standard FFV-52. It requires that table potatoes have a variety-typical appearance, be whole, sound, practically clean, and firm. A minimum size of 35 × 35 mm in square measure applies (or 28 × 28 mm for early potatoes). In Germany, the Berlin Agreements also play a central role. They define the national German potato trade conditions and serve as a voluntary but authoritative guideline for trade since the former statutory trade class regulations were abolished.
2. Typical Defect Types: What Gets Sorted Out?
Despite the best care, not every tuber grows perfectly in the ground. A study by the Bavarian State Research Centre for Agriculture (LfL) showed that on average about 11.5% of raw material weight is unsuitable for the fresh market due to external defects and must be sorted out. The most common defect types are:
- Greened tubers: At 58% of all reported defects, these are by far the most frequent issue. The UNECE standard tolerates a slight green tinge on a maximum of 1/8 of the tuber surface.
- Mechanical damage: Accounts for 17% of sorted-out produce. Cracks, cuts, and bruises must not exceed 4 mm in depth according to the UNECE standard.
- Diseases: Blemishes from the fungus Rhizoctonia solani (17%) and common scab (10%) also frequently lead to rejection. Deep scab becomes an exclusion criterion at a depth of 2 mm.
While the assessments are still often carried out visually by quality inspectors, the trend is clearly moving towards opto-electronic evaluation. Camera systems automatically scan the washed produce, count dark discolourations, measure defect areas, and objectively sort potatoes into the appropriate quality grade based on predefined parameters.
This is precisely where, in practice, the Duo85 from Karevo supports the sorting process. As a modern opto-electronic system, the Duo85 scans potatoes in continuous flow, reliably detects external defects, shape deviations, or unwanted discolourations using intelligent camera technology, and thus automates the otherwise error-prone visual inspection. The system ejects defective tubers in real time, ensuring that the produce objectively meets the required quality metrics.
Conclusion
Behind the simple table potato on the supermarket shelf lies a strict framework of agronomic planning, international standards, and precise optical assessment metrics.
References
- Arbeitsgemeinschaft der Deutschen Kartoffelwirtschaft (Ed.). (2011). Themenbibliothek Kartoffel. Deutsche Kartoffelgeschäftsbedingungen: Berliner Vereinbarungen 1956; in der Fassung vom 9. Dezember 2010. Agrimedia-Verl.
- Diepenbrock, W., Ellmer, F. & Léon, J. (2016). Ackerbau, Pflanzenbau und Pflanzenzüchtung: 68 Zeichnungen, 21 Fotos, 103 Tabellen (4th revised edition). UTB: Vol. 2629. Verlag Eugen Ulmer.
- LfL – Bayerische Landesanstalt für Landwirtschaft. (2010). Beurteilung der äußeren Qualität von Speisekartoffeln anhand von Vergleichsfotografien. LfL-Information.
- UNECE. (2017). UNECE Standard FFV-52 for the marketing and quality control of early and ware potatoes. United Nations.