Rub The Horseradish Mustard All Over The Pork Loin. Layer The Onion And Apple In The Slow Cooker, And Set The Pork Loin On Top. Pour In The Sauerkraut, Including The Juice. Season With Salt And Black Pepper, Then Add The Chicken Broth. Cover And Cook On Low Until Very Tender, 6 To 8 Hours.