In a large pot combine the spare ribs, onion, bay leaf and peppercorns, vinegar and cover with water. Bring to a simmer and cook until the meat is tender, about 1 to 1 1/2 hours. In another pot, cover the scrubbed beets with water and bring to a boil. Simmer the beets for 45 To 1 hour or until the beets are tender. Drain and rinse the beets under cold water until they are cool. Peel and grate the beets.
When the meat is tender, Remove the bones and strip off the meat in bite size pieces. Return the meat to the broth and stir in the grated beets. Season the soup with salt and pepper. In a large bowl stir together the sour cream, milk and flour. Add two cups of the hot stock to the sour cream mixture and stir to combine. Pour this mixture through a strainer into the soup. Heat the soup over medium heat at a gentle simmer, but do not allow it to boil. Boiling will cause the sour cream to curdle. Serve immediately with boiled potatoes and pumpernickel or rye bread