Serious Eats published a great article on how to cook, sear, and season their perfect steak!
TL;DR Salt your steak and rest it on a wire-rack for 40+ minutes (ideally in a fridge overnight) before searing. If you can't do that, your next best bet is to salt immediately before searing.
If you're curious to know the science behind it, here's what happens after you salt your steak (assuming it's 1.5+ inches thick):
- Within 3-4 minutes, the salt draws out liquid from the meat. At this point, you don't want to sear your steak because evaporating liquid inhibits the Maillard reaction, which forms that coveted crust around your steak.
- After 10-15 minutes, the salty brine formed around the steak breaks down the muscle fibers of the beef and starts to work its way back into the meat (!!)
- After 40 minutes, most of the liquid has worked its way back into the meat, yielding more deeply seasoned meat, and a drier exterior that's ready to sear.
You may notice that your steak appears to be slightly darker after resting it overnight -- this is normal! As it works its way into the meat, the salt actually dissolves the proteins in the meat; dissolved proteins reflect light differently than whole proteins.
The steak might also appear to be dry from the outside. Again, totally normal. Resting a steak in the fridge overnight will cause it to lose ~5% of its moisture, but this is negligible when you consider that you drive off 20%+ of a steak's moisture when you sear it.