In large heavy-bottomed pot, combine bratwurst and beer. Bring to a boil over medium-high heat. Reduce heat and simmer for 30 minutes. Preheat grill to medium-high heat (350* to 400*F). Spray grill rack with nonstick, nonflammable cooking spray. Remove brats from pot. Grill brats for 20 to 25 minutes, turning every five minutes.
Place one brat in each bun. Top with desired amount of sauerkraut and mustard and serve immediately.