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The Food Lab: Slow-Roasted Boneless Leg of Lamb With Garlic and Rosemary

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[Photographs: J. Kenji Lopez-Alt]

It always baffles me when I hear statistics about lamb consumption in the US. Compared to chicken, beef, and pork sales, lamb consumption is a drop in the bucket—two full orders of magnitude lower than chicken consumption. For every 100 pounds of chicken eaten by the average American, we consume less than a single pound of lamb!

And why? It's certainly one of the most delicious meats around, with its, er, meaty texture, and intense flavor. Is it availability? Probably not. Lack of exposure? Maybe. Or is it just that it's often not cooked very well, resulting in an overly gamey flavor and dry texture?

My bet's on the latter, and because I love lamb so hard, I'm going to try my best to remedy that situation, starting with the best way to cook a boneless leg of lamb. I'm talking about a method that delivers mild, flavorful meat with a tender texture and a perfectly rosy medium-rare hue all the way from edge to center, surrounded in a crisp layer of browned, crackly fat.

Sound good to you? Here's how we get there.

Tame the Game

Lamb meat is, by its very nature, gamey and barnyard-y tasting—it's one of the reasons why the meat is not as popular as mild chicken or beef, and while I personally love that funky aroma, when I cook for guests, I find ways to try and keep it at least slightly under wraps. Australian and New Zealand lamb tends to be smaller and milder in flavor than their larger American counterparts, but I prefer the size of American lamb legs. They're more festive, and it makes it much easier to end up with a nice rosy red center and crisp exterior.

But here's the thing: most of the compounds that give lamb—or any meat—its distinct flavor tends to be concentrated in its fat. In fact, if you grind lamb fat into a lean beef hamburger or cook a lean beef steak in rendered lamb fat, you'd swear that you were eating lamb. The lesson? Minimize the fat and you minimize the gaminess.

This is one of the many reasons I prefer cooking boneless lamb legs to on-the-bone roasts.

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Boneles lamb advantage #1: By boning out the leg and butterflying it, you get a chance to remove the large pockets of fat (which tend to be localized around a few major intermuscular glands), thereby reducing its gaminess while also making the lamb easier to carve and more pleasant to eat. Exterior crisp fat can be great, but too much soft, greasy interior fat can be excessive, even for a fat lover like myself.

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If you ask your butcher to bone out a lamb leg for you (or better yet, just buy it pre-boned), it's short work to reduce the remaining excess fat in there. To do it, work your fingers in between the individual muscle groups (It should be easy to feel where the seams are), locating the pockets of hard fat in and amongst them. Use the tip of a sharp boning or chef's knife to trim it away, leaving the fat around the exterior of the leg.

Flavor Boost

Now that we've gone and tamed all that flavor, it's time to add back some stuff to bump it up again. This brings us to the next advantage of boning out a lamb leg.

Boneless lamb advantage #2: you can season it inside and out.

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There are many flavor combinations that go well with lamb—a good North African ras el hanout rub or a slathering of harissa paste with minced garlic. Olive paste with mediterranean herbs. Even plain old salt and pepper, if all you want to taste is the meat.

This time, I'm going with the classic combination of garlic, rosemary, and lemon zest, along with some shallots, which bring their milder allium sweetness to the mix.

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Both garlic and onions change in flavor as they're heated and don't really lose their raw, pungent edge and attain sweetness until they hit well into the 300°+ range. Since we're not cooking the interior of our lamb leg beyond a medium to medium-rare 135°F and our aromatic blend is being applied directly to the interior of the roast, it needs to be cooked before it goes on the lamb.

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I cook it down in olive oil, adding a pinch of red pepper flakes for heat, and a few minced anchovy filets (another classic lamb pairing). And don't worry, those filets won't taste fishy in the final roast. All they do is boost the meatiness of the lamb by providing a concentrated source of glutamic and inosinic acids, two proteins that trigger our sensation of savoriness.

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The final component of the blend is the most important: salt.

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Salt is not only essential from a flavor standpoint, but it can greatly impact how much moisture meat retains. While its effects are most prominent in lean, white meats like pork and poultry, red meats can also benefit from an effect called dry-brining. Essentially, salt will dissolve a specific meat protein called myosin, one of the proteins responsible for the shrinkage that occurs when muscles are cooked. By dissolving this protein, you reduce shrinkage, thereby reducing moisture loss.

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So, well-salted meat not only tastes juicier because salt triggers saliva production as we chew, but it actually is juicier—measurably so. For white meat, this difference can be greater than 10%. For red meat, it's slightly less, but it's still present, and the better the penetration and the longer you let salted meat rest, the more pronounced the effect will be.

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That's why when applying a rub, it's important to really work the salt deep into as many cracks and crevasses as possible. Ideally, you want to let the mixture sit on the lamb for at least a day, though with the low-and-slow cook we're going to do down the line, there's still a good amount of time for that salt to do its magic, even if you decide to cook the leg immediately.

Roll and Tie

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With the rub applied, it's time to roll and tie the roast. If you've ever had any sort of thoughts tending towards bondage-type scenarios, this is a great way to work them out. Not that I have. Or something.

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What does all that binding tying do for us? Glad you asked.

Boneless lamb advantage #3: an even shape makes for even cooking.

A bone-in leg of lamb resembles a cone, with a very thin tapered end and a fat end. Because of this, cooking it evenly is a nearly impossible task: the meat on the thinner end is inevitably going to cook more than the meat on the fat end. This is fine if you've got an uncle or a strange cousin-type thing who enjoys dry, gray meat—heck, it even lets you question their life choices, making for great family dinner table conversation—but assuming that rare to medium meat is on everybody's agenda, a more or less cylindrical shape is what you're after.

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Taking Temps

From previous testing with prime rib, I know that the amount of moisture a piece of meat loses is directly related to the final temperature to which it is cooked. The higher the final temp, the more moisture it loses, and the dryer it tastes.

I also know that higher oven temperatures lead to a bigger temperature gradient within the meat: with a very hot oven, you wind up with a large degree of overcooked meat around the exterior of the roast, which appears as a distinct gray band.

That said, there's a balance to be struck: with lower temperatures, cooking times can get excessively long. I'll generally commit to cooking a prime rib in a 175° to 200°F oven once a year, monitoring it for its 8 to 10 hour cook time. In this case, I found that three hours at 275°F offered my the best balance between good results and a reasonable timeframe.

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A good leave-in probe thermometer like the Chefalarm from Thermoworks can be a good early warning system to let you know when your roast is approaching its final temperature, but it's not one that I'd rely on 100%. In my testing, I've found that thermometers with probes on leads tend to give less reliable readings over time (especially if you use them in hot ovens or pinch their cables in oven doors often). It's also impossible to properly gauge where the coolest part of the roast is going to be before it is actually cooked, which means that you need to remove the hot probe and repeatedly test as you approach the last stages of cooking, anyway.

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You're better off using the probe as a reminder, but still relying on a good instant read like the Thermapen for the final verification stages.

I like my lamb slightly more well done than I like my beef—a medium/medium-rare 130°F to 135°F is about right. The lamb's internal temperature will continue to rise by about 5°F as it rests outside of the oven, so make sure to take that into account when removing it (you may have noticed I accidentally slightly overcooked mine. I blame the dogs and a finicky photography setup).

Boneless lamb advantage #4: it's easier to take the temperature of a boneless lamb leg. Different materials conduct heat differently. In a lamb leg, the meat is the most efficient heat conductor, followed by the fat. The bone is by far the least efficient, which means that sections of the meat closest to the bone can end up significantly more rare than the rest of the meat. This potentially leads to false-negative temperature readings: if your thermometer's probe is resting too close to the bone, you'll end up accidentally overcooking the rest of the meat.

With a boneless lamb leg, this isn't an issue: the coolest spot in the center of the roast will not be significantly different from the hottest part in the center of the roast.

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The lamb is out and perfectly edible, but there's a difference between edible and fan-f&%king-tastic. That difference usually comes down to how crisp the fat is.

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After the lamb has rested for half an hour or so (which gives ample time for temperature differentials inside to even out), I pop it back into a 500°F oven for about 15 minutes to fully crisp. The lamb fat crackles and those bits of garlic and shallot brown, lending a rich sweetness to the salty crust. It's all I can do to stop myself from picking it off before I get a chance to serve it.

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But first, we must release the prisoner from its restrictions. Scissors are the best tools for this job, followed by carefully slipping the strings off so as not to take any of that crust with them.

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I'm sure you can guess what the final boneless lamb advantage is, but we've set up a basic rubric, so let's follow it:

Boneless lamb advantage #5: It's darn easy to slice and serve.

Your meat should be gloriously juicy, crispy on the outside, and because of its low, slow cooking, perfectly evenly cooked and extra-tender.

And on the off-chance that you end up with any leftovers? What then?

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Might I suggest some cold lamb sandwiches? I might?! Joy!

About the author: J. Kenji Lopez-Alt is the Chief Creative Officer of Serious Eats where he likes to explore the science of home cooking in his weekly column The Food Lab. You can follow him at @thefoodlab on Twitter, or at The Food Lab on Facebook.

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