There is nothing like a big, beautiful joint of rare roast beef. Richly browned on the outside, rare and juicy on the inside, perfuming the air with its savoury smells, a good roast trumps just about any other meal. Unfortunately, the next day things are different. It is difficult to reheat leftover roast without it becoming well done, a terrible thing to those who love their beef rare. Fortunately, there are a few techniques to minimise the effects of reheating.
Place a piece of leftover roast beef, no larger than 450 g (1 lb) on a sheet of heavy-duty aluminium foil. Spoon pan juices from the roast over the top, then seal up the edges of the sheet to make an airtight pocket. Reheat in your oven at the lowest temperature, until just warm. The beef should be no more than medium rare when sliced.
Slice the leftover beef thinly. Stack several slices to make a pile around 2.5 cm (1 inch) thick, with a small amount of pan juice spooned in between the slices. Wrap tightly in foil, and place in your oven at the lowest possible setting until warmed through, which takes about 25 to 30 minutes. The top and bottom slices will be cooked, but those in the middle should be no more than medium rare.
Slice the leftover beef thinly. Stack several slices to make a pile around 2.5 cm (1 inch) thick. Turn on your vacuum sealer. Place the sliced meat in the first bag, with a spoonful of pan juices. Vacuum seal the bag. Heat water in a small saucepan until it reaches a temperature of 57 degrees C (135F). Drop the sealed bag of beef into the water, and monitor the temperature closely. As long as it does not go above 57 degrees C (135F), it is not possible for the beef to cook beyond rare. Remove from the water bath and use as desired.
Low-temperature reheating techniques should not be used for larger pieces of meat, because of the risk of food-borne illness. Slice the meat into single portions for reheating, or reheat quickly at a higher temperature.