Preheat oven to 375F. Cut trimmed roast in half, if necessary, and place in roasting pan. Salt and pepper to taste. Combine all ingredients except flour and water; pour over roast. Cover and cook for 2-3 hours until roast is tender. Drain pineapple and reserve cooking liquid. Return meat and pineapple to cooker. Add water to liquid to make 1 3/4 cups. Pour into saucepan. Blend flour and cold water together to form a smooth paste. Stir into hot reserved liquid. Cook and stir until thickened. Pour over roast; serve with rice, if desired.