Potatoes for processing into starch need to be handled with some care to avoid that foreign fragments mingle with potato tuber cells and starch. No occurrence of black spots and corky spots is allowed above a certain limit because this makes refining later more difficult as such defects encapsulate soil particles. The potatoes arrive by lorry and then are fed to the processing lines of the factory by water jets or conveyor belts. After destoning and cleaning the tubers are rasped to mush containing potato juice, fiber and starch. Sulphur dioxide gas or sodium-bisulfite solution is added to prevent enzymatic discoloration and to keep the light color of the mush.