Cream butter and sugar until light. Add eggs, one at a time, beating well after each addition. Blend in vanilla. Sift cocoa, flour, baking powder, soda and salt together. Add to creamed mixture alternately with beer, beginning and ending with dry ingredients. Stir in sauerkraut. Raisins and nuts are optional. Turn into two 8 or 23 cm greased and floured cake pans. Bake at 180ºC or 35 minutes. Cool and frost as desired.