Came across a great article today on The Food Lab about the science of letting meat rest. This is something which should be done with all red meat, whether you are cooking a steak or a large fillet.
It has to do with the fibres inside the meat. The fibres act like straws. As you cook the meat the ends of the straws closest to the heat contract and get thinner forcing moisture to the cooler centre. As the internal temperature gets hotter the ‘straw’ in the middle also starts to contract forcing the moisture out onto the hot plate. That’s the sizzle sound you get when you’re cooking.
There’s an optimal temperature before that moisture starts to squirt all those juices away – it’s around 125ºF, or 51.7ºC. That’s the maximum temperature you want the inside of your steak to be if you like medium rare.
What happens then if you cut straight into the meat after taking it off the hot-plate? All the pressure building up on the inside of the meat needs to escape and so as soon as you cut – whoosh – all that delicious meat juice oozes out, lost forever.
If you wait ten minutes then the straws of fibre in the meat relax and aren’t in such a hurry to lose that juice – in other words that steak is happy to hold onto all that goodness, resulting in a tender, more relaxed and tender meat.
The way to rest it is keep it warm, not hot – and loosely covered with foil.
The bigger the meat the longer you need to rest it. The Food Lab recommend up to 45 minutes for a prime rib. Personally I can’t wait that long and I think that the extremities of the meat will have cooled so much quicker than the inside that you end up with cold meat. For me it’s a balancing act – I just tend to do it by feel.