Choosing Ingredients

Wheat flour is most commonly used to crust a roast. But if you are gluten-sensitive or simply avoiding refined wheat flour, you can also use sweet rice flour. Spicy, dry mustard works well with a flour crust, though any sort of mustard will do. Salt and pepper help bring out the flavor of the beef. Table salt and finely ground pepper work, though coarse salt and cracked black pepper are more intense in flavor. You can make the paste with water, olive oil or canola oil.

Mixing the Paste

The proportion of flour to mustard will not have any effect on the cooking process, but it will certainly have an impact on the flavor of your roast. Start with about 1/2 cup of flour and add a teaspoon or two of dried mustard, and salt and pepper to taste. Mix the ingredients with a fork or your fingers. Drizzle water or oil into the mixture, stirring it briskly until it forms a thick paste. If it is too thin, add more flour and season it accordingly. The paste should be the consistency of tomato paste or creamy peanut butter so that it will adhere properly to the roast.

Applying the Paste

The best way to apply any rub or paste is with clean hands. Wash your hands in hot, soapy water. Rinse the roast with cool water and pat it dry with paper towels. Massage the paste into the roast with your fingertips until it is completely covered.

Sealing the Crust

Sealing the crust can be done in one of two ways. You can roast the meat at a very high temperature -- 400 to 500 degrees Fahrenheit-- or you can sear it in hot oil. Searing the beef makes for a thicker, crisper crust and ensures that you kill any bacteria that might be developing on the outer skin of the roast. To sear the roast in the oven, cook it at the higher temperature for no more than 15 to 20 minutes, and then lower the temperature for the remainder of the cooking time. To pan-sear the roast, heat oil in a heavy skillet or Dutch oven, brown all sides of the flour-pasted roast for two or three minutes or until a dark crust forms.

Cooking the Roast

Cook the rib roast for 30 to 40 minutes per pound at 350 F, or according to the temperature and time recommended by your favorite recipe. The U.S. Department of Agriculture recommends cooking beef to an internal temperature of 145 F. Beef continues to cook as it rests, so for very rare rib roast, remove it from the oven when it reaches an internal temperature of 135 F.