Octopus. There may be no single food that's inspired more ridiculous cooking tricks to try to coax out faster, better results. There are the crusaders of corks, the vinegar votaries, the believers in bashing, the disciples of daikon, and the supporters of salt-kneading. They offer theories about the tenderizing effects of enzymes and tannins and acetic acid and brines—and, in some cases, like with the acetic acid in vinegar, there's even truth to the strategy—but ultimately, octopus still takes a long time to cook and strikes fear into the rubbery hearts of home cooks everywhere.
Well, I'm here to tell you two things. First, forget those tricks: Most don't work to overcome the basic task at hand (which is to cook the octopus long enough to tenderize it), and the ones that do will shave off at best a few minutes. Second, if you really want a rock-solid method for cooking octopus to tenderness quickly, all you need to do is grab a pressure cooker. Just how fast does a pressure cooker transform an octopus from a chew toy to totally chewable? Try 15 minutes. All those cork people can go...put a cork in it.
Let's back up for just a second to remember why octopus starts off tough. It all has to do with collagen, the incredibly strong connective tissue. According to Harold McGee, octopuses and related cephalopods, like squid and cuttlefish, have three to five times more collagen in their muscles than most other fish, and, on top of that, the collagen is heavily cross-linked, leading to enhanced strength and therefore toughness.
The secret to breaking down collagen is long, slow cooking, which transforms it into succulent gelatin—the same process that happens with tough cuts of meat. And yet, no one says that the secret to tender braised beef is to cook it with corks in the braising liquid! In the end, even if there are tenderizing tricks, like acid or a thorough pummeling of the meat in question, the only real way to get tender results is time—at a high enough temperature, of course.
One tip that I've heard for years is that frozen octopus cooks up more tender than fresh, the thinking being that the ice crystals that form within the flesh during freezing make micro-lacerations that tenderize the meat. This one actually does make a lot of sense to me, but I've never had much luck testing it side by side, since truly fresh octopus is hard to come by. (Don't make the mistake of assuming that the unfrozen octopus at your fishmonger hasn't been frozen before; like shrimp, it almost always has.) Still, even though I'll happily buy frozen octopus with the hope that it'll give me an edge in the quest for tenderness, it requires the same lengthy cooking that all octopus does.
The one exception to this: using a pressure cooker. It works by trapping steam to create a high-pressure cooking environment; this in turn raises the boiling point of the liquid inside the pressure cooker above sea level's standard 212°F (100°C), speeding up the breakdown of collagen into gelatin.
In my tests, a two-and-a-half-pound octopus became perfectly tender in a pressure cooker after just 15 minutes at high pressure. This doesn't include the time it takes for the cooker to reach high pressure, but even when you factor that in—about 10 minutes on my pressure cooker—it's still significantly faster than standard octopus cooking times, which I've seen range from about an hour up to a few hours. (Why, exactly, such a wide range of cooking times exists for octopus is something I still haven't figured out... clearly not all octopodes are created equal.)
I did my tests, using several octopuses of similar size, on a Breville electric pressure cooker (it runs at around 12 psi) and on a stovetop Kuhn Rikon (at 15 psi), both of which I recommend, and had just about the same outcome with the cooking time. It's possible that the timing may vary depending on the size of the octopus, its general tendency toward tenderness, and the pressure cooker used, but so far I've had fairly consistent results.
Once your octopus is done, you can let it cool in its cooking liquid, then cut it up as desired. Just remember to remove the beak if it's there (you can find it in the center of the underside of the octopus, where the tentacles converge), as well as the eyes. I eat all the other parts, including most of the head, but make sure to wash the inside of it well before cooking, since sand often lurks in there.
You can then cut up the octopus and toss it into seafood salads or ceviches, or sear the whole tentacles in a skillet or grill them over direct heat until charred and crispy. The pressure cooker may not have the mystical allure of some of the other ideas bobbing around out there, but it's so consistently speedy and successful that it makes all those other techniques moot.