If you cut the steak open when it is hot, the juices on the inside will run out and the steak will dry out and get chewy. If you let it sit 5/10 minutes, the juices will hold in the steak and it will be perfect. This is true of almost ALL meat.
Before You Cut…
The reason behind resting is that steak needs a few minutes after cooking to let its juices run back through it. If you slice it immediately, you'll lose all those juices on your plate, leaving the steak dryer and chewier than it would be if you let it rest for a few minutes.
According to Serious Eats, cutting into your steak while it's still sizzling in the pan will yield inaccurate results. This is because the juices that emerge from the hot steak will make it look much rarer than it actually is.
Internal juices constrict during the cooking process, and resting meat allows its juices to reabsorb and redistribute. Cutting it too soon will cause its juice to pool out and yield a dry cut of meat.
Always slice against the grain or perpendicular to the grain. The grain is the direction that the muscle fibers are aligned in a steak. When you cut the steak against the grain, you shorten the muscle fibers, which makes for a very tender bite.
First, Let it Rest!
No matter the type of steak you've cooked up, you want it to be juicy and tender when cut into. For a decent sized steak, resting for about 10 minutes after grilling allows for the juices to evenly distribute and significantly adds to the flavor of your entire steak.
The whole goal of slicing against the grain is to reduce the length of the muscle fibers to make chewing easier. Not to mention, this technique locks in those juices.
Marinating allows the muscle fibers in the meat to soak up flavor before hitting the grill. Cut slits into the steak before marinating to allow the flavor to penetrate deeper into the meat.
Slicing the meat will allow you to develop better flavor on more seared surfaces, though. And the marinade will be more effective and will be absorbed a bit more into the meat (with more surface area), thereby somewhat offsetting the moisture loss during cooking.
The main claim to flipping only once is that you'll reduce the amount of browning that will occur and also reduce the flavor. While this can be true, you can easily avoid this drawback by ensuring you do not have an overabundance of surface moisture on your steak and have sufficiently high heat.
The longer you cook a steak, the hotter it gets, and as it heats up, the muscle fibers get firm and all the juices cook out. The result is that the interior of a well-done steak is a uniform gray color, and the steak itself is tough, chewy, flavorless, and dry. This isn't cooking; it's arson.
The center of the steak becomes supersaturated with liquid—there's more liquid in there than it can hold on to—so when you slice it open, all that extra liquid pours out. By resting the steaks, you allow all that liquid that was forced out of the edges and into the center time to migrate back out to the edges.
Have you ever wondered what they are doing? Here's the answer: they're feeling for the state of doneness. With just a touch, a skilled cook can judge if a piece of meat is done or if it needs more cooking. They're feeling for a degree of softness or firmness in the meat.
Most chefs regard beef cooked to medium-rare — with an internal temperature of 130-135F (55-57C) — as the best way to bring out flavour and retain moisture in tender cuts such as rib eye and top loin. Unlike rare, medium-rare allows time for the outside to caramelise and develop a sear.
However, every great steakhouse seasons the steaks they cook. Typically a steak is seasoned with coarse ground black pepper, sea or kosher salt, garlic, and some type of signature spice. In addition to the seasoning most steakhouse's use a marinade, butter, or some type of baste or finishing liquid.
Probing also helps you know the meat temperature to avoid overcooking. Another benefit that has been associated with poking holes in raw meat is that it helps tenderize the meat. The piercings allow heat to penetrate deeper when cooking, cutting down on the cooking time and making the meat tender.
Tenderizing The Steaks
The first method, and arguably the fastest, is using a fork. Just go over the entire steak, puncturing holes all over. Then flip and repeat. The idea is that opening lots of holes helps moisture escape during cooking.
TL;DR: Yes, it's fine to cut meats before cooking. Another option to pan cooking You might consider using a sous vide cooker (or water bath with a good thermometer) to thoroughly cook the meat before searing.
Your best bet for achieving marination magic is to soak your chicken, pork chops or loins and steak at least 30 minutes, but never longer than overnight.
Why Marinate Foods? Marinating is an effective way to enhance the flavor, add extra moisture, and tenderize meat before cooking. In addition, a good marinade can help make leaner cuts less dry and make tougher pieces of meat more succulent. People have been soaking their meats in seasoned liquid for centuries.
If you do cut with the grain of the steak, you will often find the meat more gamey and tougher to chew. The reason? It is because the long muscle fibers remain intact and haven't been cut. Cutting against the grain breaks up the muscle fibers making the steak much more tender.
The method is basically “3-3-3-3.” That means: grill steak side 1 over direct heat for 3 minutes. grill steak side 2 over direct heat for 3 minutes. Flip steak and grill on side 1 over indirect heat for 3 minutes.