I understand that when a steak rests after cooking, the muscle fibers relax, allowing the juices to reenter the meat as described here. I've heard that while the meat relaxes and the juices flow in, they can draw melted butter in as well. Is this true? I've tried the technique and find it tastes great, but I'm not sure if its because the butter really penetrated or because the surface is just coated with it.
Meat – Does butter really penetrate a steak when allowing it to rest after cooking
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There are a couple of reasons why 'resting' meat is a good idea. First, as the meat cooks the muscle fibres contract, which forces the juices out. Letting the meat rest helps the muscle fibres relax so the juices are re-incorporated into the meat and not lost on the chopping board, which would happen if carved immediately.
The second reason to let meat rest is to provide an evenness. Basically as the meat rests it continues to cook slightly and it allows the meat to gain an overall 'doneness'
The one problem I see with the article is that they cook the steak "as is" after letting it rest. They even mention that because so much liquid had been pulled out it caused problems with cooking. The missing step is to pat the steak dry. It needs to be dry when going in to the pan. I think the results are slightly skewed because of this - it was dry at the 0 minute mark and at the 40 minute mark but not at the in between marks. Keep in mind that you can wipe off seasonings when patting dry so this is still something to keep in mind.
As for your question - how long to leave it out? As Aaronaught said it doesn't really matter if it's salted or not. How long a steak can sit on the counter and not go bad will depend on the conditions and is more of a food-safety question unrelated to seasoning. You can, as the article mentions, place it in the fridge if you want to let it rest for a long time. Just remember to let it come back to room temperature before cooking for best results.
I'm not sure I really buy in to the importance of water reabsorption in how it relates to taste. The entire process of dry aging is designed to pull moisture out of the meat to give it a more concentrated beef flavor. Again, the article mentions that letting it rest this way for up to a day only results in an ~5% loss by weight, which pales in comparison to the 20%+ loss from cooking.
Now if you want to let it "rest" for a LONG time, like days or weeks you're talking more about a process like dry aging, in which case you'll want to start with a large piece of meat as the outside will need to be cut off as it will get rather dried out and not very appealing to eat. This involves more than just putting meat in the fridge though, so you probably don't want to go too far past 24 hours in the fridge.
Best Answer
I'm not sure the butter penetrates, but it tastes pretty good on the surface. ;)
I think it's pretty obvious that marbling plays a huge role in juiciness, so it stands to reason that if you bard or lard the meat it would also make a difference in juiciness (and indeed, the standard filet mignon with the bacon barding would seem to bear this out).
In the end though, it's always been my experience that once you cook the juice out of something, it's gone for good. I've always considered the idea of "resting" meat to be more about letting it cool to the point where the temperature isn't going to force out juice that would otherwise linger.