A roast is low in fat, which makes it susceptible to drying out. Larger roasts will need some additional liquid for cooking. A mix of wine and water works well, and aromatics like peppercorns and bay leaf can be added for extra flavor.
Small roasts can cook quickly enough they won't need additional liquid. These can be cooked like this:
A kilo is about two and a quarter pounds. He's setting the oven to 450 degrees Fahrenheit, although most large roast recipes will recommend a temperature around 325.
No matter how you cook your roast, it should first be seared. Searing the meat causes a Maillard reaction, creating new and tasty protein chemicals that will add a lot of flavor to the roast. It does not "seal in the juices," which you wouldn't want anyway because those drippings will make a great gravy.
The size and shape of a roast can vary a lot, so the only way to guarantee it's perfectly done is with a probe thermometer. This device will constantly monitor the inside temperature of the roast, letting you know exactly when its done. The roast should reach 125 degrees Fahrenheit (52 Celsius) to be cooked rare, 130 degrees Fahrenheit (55 Celsius) for medium rare, and 145 degrees Fahrenheit (63 Celsius) for medium. When the roast is removed from oven, the heat on the exterior of the meat will continue to reach into the interior, raising the temperature a degree or two.
Once the meat is done, it needs to be covered and allowed to rest for a few minutes. The heat coils up the proteins, releasing the interior fluids; letting it cool lets these proteins relax, reabsorbing the fluid. If you used a probe thermometer, leave the probe in to keep juices escaping from the hole.
Posted 3420 day ago