you must marinate it at least two days -- I usually do it for 4-5 days.
Sauerbraten (serves 10)

4 lb. top or bottom round roast
1 cup red wine
1 1/2 tsp. salt
10 peppercorns, crushed
1 onion, sliced thin
2 bay leaves
3 Tblsp. pickling spices
1/2 cup ( 1dL) gingersnaps, crushed fine
1/2 cup sour cream

Two days before you plan to use it, put beef into a glass or pottery bowl. In saucepan, mix wine, onions and spices and 2 cups water, bring to a boil and remove from heat. When it is cool, pour over beef, cover and refrigerate until day you plan to use it. Turn it in the marinade several times each day

Melt a little shortening in a dutch oven or casserole and pat the meat dry with paper towels, then brown roast on all sides .Drain off the fat, strain the marinade over the roast, cover it and cook in the oven for 2 to 2 1/2 hours, or until tender. Remove the meat to a platter and keep warm.. Bring liquid in pan to a boil and add the gingersnaps, stirring while the gravy thickens. (at this point, I add a little cornstarch mixed with a little cold water, to thicken it a little more.) When the gravy is thickened to your liking, stir in the sour cream but do not let it boil -- just heat it. Pour gravy into sauce bowl, slice the roast andserve.