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The Food Lab: How To Make The Best Fajitas
It's time for another round of The Food Lab. Got a suggestion for an upcoming topic? Email Kenji here, and he'll do his best to answer your queries in a future post. Become a fan of The Food Lab on Facebook or follow it on Twitter for play-by-plays on future kitchen tests and recipe experiments.
I'm not particularly proud of my time time spent working at the kinds of cheesy chain restaurants you'd find next to the Victoria's Secret at the mall, or perhaps in Times Square. But aside from making me shun any writer that uses the phrase "X to perfection," it did teach me one valuable lesson: People looooooove meat served on a sizzling platter. It was a well-known phenomenon: If a waiter could sell one order of our Extreme Fajitas™ to a table in their section, a half dozen more orders would quickly follow.
It's an unstoppable, visceral reaction. The waiter would plot a circuitous route around the restaurant that would take the platter past as many intermediary tables as possible. The approaching noise of sizzling meat would halt all conversation in its tracks as diners would gently lift their chins, tilting their noses in the air to catch a whiff of beef, onion, garlic, and chili as their aroma wafted by on thin whisps of smoke and steam.
Then of course, there's the DIY aspect of fajitas that makes them a winner. As a kid, there's nothing better than being presented with that plate of guacamole, pico de gallo, and sour cream; the anticipation of that sizzling platter of meat and vegetables laid down before you. When they arrive, you've already picked out a soft, blistered floured tortilla from the steaming stack in the warmer at the center of the table.
The meat itself should be ultra-juicy, with an overwhelming, almost buttery beefiness—this is skirt steak, after all, the butteriest of all beef—accented by a marinade that is slightly sweet, very savory, and packed with lime and chili.
And of course, that meat's got to be tender. Nothing worse than biting into a carefully wrapped fajita only to have that long strip of beef slip out of its tortilla housing like a sleeping camper from his sleeping bag. Better to be able to bite that camper in half, right?
So how do we reach this fajita nirvana? It's easier than you think—all it takes is a bit of strategy and know how.
When you grow up eating something, it's hard to remember that at one point it didn't exist. "Fajita" literally translates to "little skirts" or "little bands," and it stems from the appearance of a skirt steak, a thin flap of meat that hangs down near the front of the steer's belly. The history of fajitas in most of the United States is very recent. According to an excellent article in the Austin Chronicle, there's anecdotal evidence that South and West Texas vaqueros and butchers have been eating grilled skirt steak and calling them fajitas since the 1930s.
Fajitas appear to have made the quantum leap from campfire and backyard grill obscurity to commercial sales in 1969. Sonny Falcon, an Austin meat market manager, operated the first commercial fajita taco concession stand at a rural Dies Y Seis celebration in tiny Kyle in September of 1969. That same year, fajitas debuted on the menu at Otilia Garza's Round-Up Restaurant in the Rio Grande Valley community of Pharr.
Residents and visitors of Houston might be happy to know that Ninfa's on Navigation Boulevard is one of the oldest fajita-slinging restaurants in the country, though when I visited them last summer, I was more impressed by the quality of their cooked-to-order flour tortillas than the fajitas themselves.
The fajita made its final jump into the spotlight when George Weidmann of the Hyatt Regency in Austin added the sizzling platter that shot the dish into stardom, making it a staple on not just the Hyatt menu, but on menus across the country.
Now, with all this popularity, you may smell a problem: supply. See, there are only four skirts on each steer—two inside and two outside. That's about 8 pounds of meat total. As a result, restaurants started resorting to other cuts to make their fajitas.
First it was hanger, sirloin flap, and flank steak—all reasonably good options with a similar texture and flavor. But as things progressed, the dish moved farther and farther from the original, leading us to not just other cuts of beef, but chicken fajitas, pork fajitas, shrimp fajitas, and the like.
Even McDonald's jumped into the fajita game in 1991 (the 12-year-old-me was a big fan).
I tested cooking fajitas with a variety of cuts—skirt, hanger, flap, flank, short rib, and tri-tip. Of these, skirt, hanger, and flap were the most successful, each with a robust, coarse texture that is great for soaking up marinade.
But there's no doubt about it: the skirt is king. It's more buttery, more beefy, and just plain more tasty than its counterparts.
While fajitas are traditionally made with outside skirt—part of the diaphragm muscle of the steer—the cut is pretty much unavailable unless you work for a restaurant that special orders it. At the butcher or meat counter, you're far more likely to find inside skirt, which will do us just fine.
The key is to not trim off too much of the fat that covers one side of the steak. They'll melt into the cracks as the meat grills, making each bite juicier and tastier.
While it's possible to cook the steak as a whole strip, I find it better to slice it with the grain into 5 to 6-inch pieces, making it easer to handle them on the grill.
Next up: we've got our meat, so how do we treat it?
It's proven difficult to pinpoint exactly what ingredients went into the original fajitas marinades, but it's a safe bet that at least some chilies, garlic, black pepper, and cumin were involved. All of these are flavoring ingredients—they don't really change the manner in which the meat cooks or interact with it on more than a cursory level. What about some other common marinade ingredients? Ones that might actually affect the meat more intimately?
I tested out over two dozen marinade variations, adding extra ingredients to some (ranging from commercial meat tenderizers to natural enzymatic tenderizers like pineapple and papaya) and omitting ingredients from others (in order to see what happens when, say, you forget the oil in a marinade).
I even took photos of every steak in the process, but unfortunately, from a visual standpoint, you can't really see much difference. Just imagine slightly different versions of this 26 times in a row, and you'll get the picture:
What I found was that in addition to basic flavoring agents like chili and garlic and a touch of sugar to aid in browning, the best marinades share three common ingredients: oil, acid, and a salty liquid, preferably a protease (more on those later).
Key To Great Marinades #1: Oil
Oil is essential for three purposes. First, it emulsifies the marinade, making it thicker and tackier, causing it to stick more efficiently to the meat. Second, many of the flavorful compounds found in the garlic and ground spices in the marinade are oil soluble. With a fat-based medium coating the meat, you get better, more even flavor distribution. Finally, the oil helps the meat cook more evenly, providing a buffer between the heat of the grill and the surface of the meat to spread that heat evenly. Omitting it detracts from all three of these qualities.
Key To Great Marinades #2: Acid
I used to think that acid was essential in a marinade for tenderizing purposes, and it's true—acid can slightly tenderize tough connective tissue in meat. Unfortunately, excessive acid can also start to chemically "cook" meat, denaturing its protein and causing it to firm up and eventually turn chalky (think: ceviche).
I tried completely omitting acid, adding it in the form of lime juice squeezed on at the end, but the flavor difference was noticeably—meat marinated in acid was more balanced and brighter tasting. There were also a few minor strands of membrane and connective tissue that were more noticeable without the acid. In the end I opted for lime juice in equal parts with the oil.
You may be surprised to learn that despite their reputation, marinades do not actually penetrate particularly far into meat—even after the course of a night, it will penetrate no further than a millimeter or two, and that penetration rate slows down the longer you marinate for. So really, a marinade's effects are largely limited to the surface of the meat. Luckily for us, on a skirt steak, that's precisely where all of the tougher connective tissues are located, so if any tenderization is going to occur, it'll occur in the right places.
Key To Great Marinades #3: Salt and Proteases
The final ingredients in a good marinade is a salty liquid. The muscle protein myosin will dissolve in a salty liquid, leaving the meat with a looser texture and a better ability to retain moisture. This is the theory behind brining meats like chicken or pork, and the same theory applies to our fajitas.
While you could just add regular salt to the marinade, there's a lesson I learned in years of playing MarioKart: Why settle for a driver who just has good handling when you can pick a driver with good handling and a high top speed?
By replacing the salt with a good splash of soy sauce, we not only get salt into the marinade, but we also get two other important elements. First, glutamates—natural flavor enhancers responsible for the sensation of umami that makes taste meat taste meatier. Second is proteases: enzymes that help break down and tenderize tough proteins.
Soy sauce is hardly traditional, but it's got a prominent place in many fajita recipes for these very reasons. That it doesn't taste distinctly soy-like or Asian once the meat is cooked is especially nice.
Once I'd gotten my ideal marinade ratio down, I moved on to testing timing, going every from dipped-just-before-grilling to marinated for 36 hours. Again, not much visual difference. Picture this 6 times in a row:
Tastewise, however, I found the ideal timing to be between 3 and 10 hours or so. Less and the marinade simply didn't stick as well. More and the meat started to get a bit too mushy and chalky around the exterior, having a slightly cooked appearance from the lime juice and the soy sauce before it even hit the grill. My guests still happily devoured the 36-hour marinated steaks, but if you can get your timing right, it'll make the final product marginally better.
Marinate your meat in a plastic zipper-lock bag with all the air squeezed out for best contact with a minimal amount of marinade (I do this by leaving a small air hole along one edge of the zipper lock, squeezing all the air towards it, then sealing it at the last moment before juices start leaking out), or even better, seal the steaks in a cryo-vack style bag with a vacuum sealer.
There's one golden rule to cooking skirt steak: make sure your grill is hot as hell. Skirt steak is not too thick, and its loose texture allows heat to penetrate faster than in, say, a dense New York strip or ribeye. You need to absolutely pound it with heat in order to get it nice and charred on the exterior before the center ends up overcooking.
To do this, I empty out an entire full chimney of coals over just one side of my grill, piling them and allowing them to preheat until I can barely bring my hand close enough to deposit the steaks (long tongs help here). If hardwood coal is an option, I'd opt for them over briquettes—hardwood burns faster and hotter.
There are a couple of factors working to our advantage here. First is the soy sauce and sugar in the marinade, both of which will help the steaks brown more efficiently. Second is that fact that skirt is one of the cuts of steaks that benefits from being cooked slightly more than you'd normally cook a premium steak.
Anything shy of medium rare and skirt steak has a squishy, unpleasantly slippery texture. I always feel like a raptor biting into a tough Jurassic Park T-rex leg when I get an undercooked skirt. At medium-rare (around 125 to 130°F after resting—pull them off the grill at 115 to 120°F), they start to firm up to a pleasant juiciness, but personally I think skirt steak has the optimal amount of flavor and juiciness at a full 135°F medium.
Don't believe me? Just try them side-by-side and come to your own conclusion.
The last step in perfect fajita meat is by far the most important: the carving.
See, skirt steak has a very pronounced grain—muscle fibers that are all aligned in the same direction. The steak is stronger in one direction than the other. If you cut your steak with the grain, you end up with long chewy fibers. But slice it thinly against the grain and you increase its tenderness dramatically.
You can cut perfectly perpendicular to the grain for absolute tenderness, but I prefer to cut at closer to a 45 degree angle, which effectively shortens muscle fibers to about 40% more than then absolute minimum length—plenty short enough to give you tenderness, while also allowing you to cut slices that look a little wider and prettier.
See how nice they look all fanned out?
And while those sizzling fajita platters sure to a good job of selling more fajitas at restaurants, all they're going to do in your home is slowly overcook your meat. A warmed serving platter is a better vessel.
With the meat taken care of, we move on to slightly more trivial but no less important* matters: the vegetables and toppings.
*strike that, reverse it.
For vegetables, the classic choices are onions and peppers. I like to save some of my marinade to toss them with before cooking.
I tried cooking them whole on the grill, but the results are not quite right—they tend to soften more than I want them to.
Cooking them in a cast iron skillet on the stovetop works much better, but then it requires me to heat up my kitchen and my grill. I may be a fool, but I'm not that kind of fool.
Then I thought: wait a minute, Kenji, don't be an idiot: you've got yourself a heat source right here in front of your eyes. Use it!
I cooked up a batch of fajitas, letting my big cast iron skillet heat up on the cooler side of the grill while the meat cooked. Then, while the meat rested, I slid it over to the hot side and seared my veggies. It worked like a charm, giving them some nice color and sear without letting them turn too mushy or soft.
As an added bonus, the pan full of vegetables proved to be the perfect place to pour off the meat juices and drippings that collected on the platter where my steaks were resting. I always love it when I can take a zero-flavor-down-the-drain approach to dishes.
With your meat sliced and your veggies cooked, all you need is a stack of hot tortillas (you can heat them up as a whole stack on the cooler side of the grill while the veggies cook), and a few condiments.
While these fajitas might not have the sizzle of my childhood memories, they've certainly got all the swagger of a smoking hot plate weaving its way through the dining room, making everyone else envious of what you're abut to sink your teeth into...