Things You'll Need
Gravy or stock
Digital meat thermometer
Roasts lose quality during reheating, but they also cultivate bacteria from the time you take them out of the refrigerator to the time they reach 165 degrees Fahrenheit, the minimum safe serving temperature for reheated beef. Reheating often results in dry, tough meat, unless you incorporate moisture in the process. For best results, and the quickest reheating times, slice leftover roast thinly so each slice reaches the safe serving temperature at the same time.
In the Oven
Heat the oven to 350 degrees Fahrenheit. Skim and discard the fat from the sauce and bring it to a simmer in a saucepan.
Carve the roast into 1/4- to 1/2-inch-thick slices. Arrange the slices in an oven-safe dish and pour the gravy over them.
If you don't have gravy, pour about 1/4 inch of hot stock or water over the slices.
Cover the dish with foil and heat it in the oven until the slices reach 165 F, about 20 minutes. Use the tip of a digital meat thermometer to check the beef's internal temperature.
On the Stove
Skim and discard the fat from the sauce. Pour the sauce in the saucepan and heat over medium-high heat until boiling.
Carve the roast into 1/4- to 1/2-inch-thick slices. Drop two to three slices into the sauce; fewer if the pot is small. Do not overcrowd the pot.
Leave the slices in the sauce until they reach 165 F, about 5 to 10 minutes. Remove the slices and serve immediately. Use the tip of a digital meat thermometer to check the beef's internal temperature.
Never reheat beef more than once; multiple reheatings cultivate bacteria.