Why does lamb taste like lamb?

"What it all comes down to is its fat and a particular type of fatty acid that lambs have that beef doesn't," says Molly Birnbaum, executive editor of Cook's Science at America's Test Kitchen.

[More from Birnbaum: 7 tips for cooking with onions and garlic]

Sally Swift: We are in lamb season, if ever there is a lamb season in the U.S. Is there a reason that lamb tastes like lamb?

Molly Birnbaum

Molly Birnbaum: There is a big reason why lamb tastes like lamb. It is a very distinctive taste; it's one that we all recognize. It's one that some people love, and some people really, really don't love.

But what it all comes down to is its fat and a particular type of fatty acid that lambs have that beef doesn't. It's called branched-chain fatty acid. This is something that humans can detect at tiny levels. It's what gives lamb this gamy, more earthy taste than beef.

SS: The New Zealand lamb that I eat -- which is pretty much all we can find -- tastes very different to me. I find it very hard to find American lamb. Is there a difference in taste between the two of them?

MB: There is. There's a huge difference in taste between domestic lamb and most of our imported lamb, which is from New Zealand or Australia. What it comes down to is the diet of the lamb.

SS: Which would influence that fat.

MB: Yes, it influences so much, especially their fat. But New Zealand lamb is all pasture-raised, so they're farmed on grass. They eat grass for their whole life. That really brings out these branched-chain fatty acids. They're fat, so they're pretty strong-tasting. They taste like lamb. They're lambs that taste like lamb. They're a little bit less fatty, as well.

The domestic lamb, the American lamb, is a little bit milder. This is so much because American lambs are often finished on grain. For the last 30 days of their life, they eat grain. They eat grass until then, but this change in their diet changes the type and amount of fat that they have. They have less of these branched-chain fatty acids, and therefore less of that super-distinctive lamb flavor.

SS: Is there a way to control that flavor if you get rid of the fat? There's not fat on a piece of lamb, for the most part.

MB: It depends on the cut. But the best way to control the flavor, if you are eating lamb but don't want it too lamb-y, is to take off as much fat as you can. A lot of cuts have a fat cap that you can trim down.

One of my favorite cuts is a leg of lamb, which I like to have butterflied. That cut also allows you to get in there and take out the little pockets of fat that are in there. Taking out the fat is what can control the lamb flavor.

Recipe: Roast Butterflied Leg of Lamb with Coriander, Fennel, and Black Pepper Photo: Copyright 2016 America's Test Kitchen

SS: What is your favorite way for preparing a butterflied leg of lamb?

MB: We have a recipe that is really nice. My family actually made it for Christmas this year. It's a leg of lamb, boneless, butterflied. It's opened up and easier to season all over, easier to take out this fat and make it evenly spaced. We cook it low and slow to start, which helps break down the collagen.

SS: You roasted it?

MB: Yes. This is a roasted, butterflied leg of lamb. We started at a 250-degree oven, then cooked it nice and slow. It really helps to break down the tougher parts of the meat. The salt is in there, so it's super flavorful. We have an oil that's flavored with lots of spices, some lemon peel, ginger and shallots. When it reaches about 120 degrees Fahrenheit, we broil it. It gets a nice, crispy top to it.

SS: Does lamb take well to marinades and rubs, or is that a wasted step?

MB: It does. We marinate or rub a lot of different lamb. It's such a distinctive flavor that it pairs well with nice, strong spices, as well as herbs. Coriander, fennel, garlic, shallot, ginger, lemon peel --I think those work really nicely with lamb. There are other herbs that are traditionally paired with lamb, like mint. In England especially, lamb and mint is a huge thing.

SS: Lamb and bad mint jelly, to be frank.

MB: Exactly. There is a little bit of science behind that. There has been a lot of talk in recent years about flavor pairings and how different foods, even if they seem a little bit incongruous, will work together flavor-wise because they share some flavor compounds or some elements of some flavor compounds, such as chocolate and blue cheese, for example. There have been a few papers about this out there and a few startup businesses whose goal is to help chefs pair these types of foods together.

SS: Not to mention selling books.

MB: Exactly. But there is a little bit of overlap in the flavor of mint and in the flavor of lamb, especially these branched-chain fatty acids that are making up the gamy flavor. When you really deep-dive into it, there is a reason why lamb and mint go together.

Courtesy of America's Test Kitchen