Whether it is a pork tenderloin or a large beef roast, we always let meat rest after roasting.
Whether it is a pork tenderloin or a large beef roast, we always let meat rest after roasting. One of the reasons we do this is that resting allows the meat fibers—which contract when hot—to relax and reabsorb juices they’ve squeezed out. If cut too soon, the roast will release these juices onto your cutting board. In the past, we’ve gone by the rule of thumb that the larger the piece of meat, the longer it needs to rest. We wondered recently whether the oven temperature used to cook the meat also affects the resting time, so we ran an experiment.
We roasted six 1-pound pork loins; three at 250 degrees and three at 450 degrees, cooking them all to an internal temperature of 140 degrees. We then let pairs from each set rest for different amounts of time before slicing. We sliced the first set immediately, the second set after a 10-minute rest, and the third after a 20-minute rest. We then measured the amount of juices lost as a percentage of total weight for each pork loin.
Both of the roasts that were carved immediately lost a significant (and unacceptable) amount of their weight in juices (6.5 percent from the low-oven roast and 8.6 percent from the hot-oven roast). At the other end of the spectrum, the two roasts that sat for 20 minutes before slicing lost roughly equal amounts of juice (about 4 percent). The most notable difference was between the roasts that had rested for 10 minutes: The hot-oven roast lost almost twice as much juice when sliced after 10 minutes (7.9 percent) as the low-oven roast (which lost 4.3 percent).
While all of the roasts were cooked to the same internal temperature, the roasts cooked in the 450-degree ovens were significantly hotter around their perimeters than at their centers compared with the roasts cooked in the 250-degree ovens. Therefore, the muscle fibers around the perimeter in these roasts were much more contracted and needed more time to relax and reabsorb juices.
When roasting low and slow, meat needs a shorter rest than does a high-temperature roast. The muscle fibers do not tighten as much, so juices lost are minimized, and there’s nominal benefit to extra waiting time—your roast will simply cool off more.