I've been trying to troubleshoot my recent burgers based on new cookware, different stovetop and time passed since I last made decent burgers. What I forgot was that I did something else new this time: I put in spices. Salt, pepper, dried thyme, dried onion, red pepper flakes and cayenne powder. Everything but the salt and pepper will soak up moisture like crazy, and I put a bunch of it in. In effect I pre-dried my burgers. I still have 3 such patties: one in the fridge and two frozen. I guess I should thaw the frozen ones, mix it together, add some moisture and remake the patties.
So if you ever want a really dry medium-rare burger, now you know how.