Cut casings from bratwursts and combine. Divide into four equal parts and form into patties. Preheat grill. These bratwurst burgers are going to have a higher fat content that your regular burgers so grill them at a medium heat and watch for flare-ups. When burgers are cooked through (and these need to be cooked to at least medium well), remove from grill. Place on bun and top with 1/4 cup sauerkraut, pickles and mustard.