Place the sauerkraut in a sieve, rinse briefly under warm water, drain and chop coarsely. Wash the chives, shake dry and cut into fine rolls. Cut pumpernickel into cubes.
Heat 3 tablespoons of oil in a frying pan. Fry the bread cubes all around.
Cut cabanossi into thin slices. Heat 1 tablespoon of oil in a saucepan. Fry the sausage briefly. Add sauerkraut and fry for about 2 minutes. Add vegetable stock and simmer for 3-5 minutes.
Season to taste with salt and pepper. Garnish soup with chives, croutons and sour cream.