Cook beetroot, carrots and potatoes separately. Please do not overcook the carrots, they should still be firm to the bite. Cook the beetroot for about 1.5 hours (you can buy fresh cooked beetroot, which you can also use).
Cut the potatoes into approx. 2 cm cubes, beetroot and carrots approx 1.5 cm. Grate the cucumber and apple. Cut the onion into small pieces. Put everything together in a bowl and add the sauerkraut, without the juice.
Season with salt, pepper (sparingly) and sugar. Mix with oil or mayonnaise and let steep.