When America's Test Kitchen set their tasters loose on an 18-month-old wedge of Parmigiano-Reggiano, their verdict was unanimous: The closer to the rind, the better it was. Molly Birnbaum, their executive editor of Cook's Science, tells us why that is, and shares a recipe for Parmesan-Crusted Asparagus.

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Sally Swift: So what have you and your team been working on at America's Test Kitchen?

Molly Birnbaum Molly Birnbaum

Molly Birnbaum: We have been diving into the science of Parmigiano-Reggiano.

SS: So what have you discovered? New information on the goddess of cheeses?

MB: We have discovered some new information on this goddess of cheeses. It's actually a very simple discovery that we've made, but one that has practical applications for the home cook.

SS: And you're talking about the real Parmesan, the Parmigiano-Reggiano, with the D.O.C. from Italy. This is the real stuff?

MB: Exactly, we're talking the real stuff. In general, a wheel of Parmigiano-Reggiano weighs 84 pounds and can measure up to 18 inches wide and nine inches tall. This is a huge thing. It is a very big wheel of cheese.

We purchase quarter wheels, not a whole wheel, but it’s still a significant amount of cheese that lasts for months in our kitchen. What we do is break it down, so everyone can have their own manageable pieces of this cheese, and in the process of breaking down this quarter wheel, we noticed a big difference between the cheese at the rind and the cheese at the inner part of the wheel. It almost seemed like they were two different cheeses.

We wanted to kind of get to the bottom of that, so we did blind tastings of samples of cheese taken from a bunch of different locations on a wheel of 18-month-old Parmigiano-Reggiano, mainly from the outside and from the very center of the wheel. We asked the tasters to describe the flavor of each sample and rank them; they unanimously loved the samples from the outside of the cheese close to the rind.

SS: Wow, that's crazy! Everyone?

MB: Everyone. And there's a huge difference. The words they used to describe it were much more nutty, much more complex with a sharp flavor. Pleasantly crumbly. The samples from the center of the wheel ranked last and were described more as clean-tasting and smoother with a little bit of a plastic-y texture.

Those are huge differences. We wanted to know why, and what it comes down to is that, when cheese ages, it undergoes a very complex process called proteolysis, and this impacts the texture and the melting qualities. Basically, the casein proteins, which are the most important proteins in milk and play a huge role in cheese, they kind of bind with each other, creating this very strong network. Water evaporates, it becomes a very strong, aged thing, and it affects the flavor pretty significantly.

In this process, which happens from the outside of the rind going in, there are little white crystals and larger round pearls that are formed through the process of proteolysis, and they're definitely not defects. You'll notice them when you eat cheese, they're kind of crunchy and super delicious.

They're found in aged cheese, mainly, and we found that the crystals and the pearls were much more prolific on the outside of the cheese than the inside, and that's because of the process of aging happens from the outside in. We wanted to find out a little bit more about what those actually were because we realized we had no idea.

In the process of researching that, we found out that the scientific community also didn't really have an idea of what those crystals and pearls were until last year. There was a paper published in Dairy Science and Technology in 2015, announcing the discovery of what these crystals actually were. And it was research conducted at the University of Vermont, using an instrument called a powder x-ray diffractometer.

SS: Wow, how exciting.

big parm Parmigiano-Reggiano Photo: Michael Blann/Thinkstock

MB: I don't even know what that looks like, but it's very cool, and what they found out was that the tiny white crystals in Parmesan are composed of an amino acid called tyrosine, while the small white pearls turn out to be a crystalline form of the amino acid called leucine. That was a big discovery in the Parmesan world.

SS: And they're delicious.

MB: They're delicious. That's what you want. You want to get a piece of Parmesan close to the rind, because you want that crumbly texture, that nutty flavor, and as many of those tyrosine and leucine crystals and pearls as you possibly can.

SS: So you're looking, in the best of all possible worlds, for a corner piece.

MB: A corner piece is exactly what you want.

SS: And can you tell us how we know we're buying the real Parmigiano-Reggiano?

MB: Yes. The real Parmigiano-Reggiano has a stamp on the rind, so you can see that it's actually there.

SS: So almost always better to buy a rind piece, then, so you know what you’re getting.

MB: For multiple reasons, yes.

SS: So give me an idea of a recipe you love to make with Parmesan.

MB: Something that I love to make is a Parmesan-crusted asparagus. This is a recipe that we developed at America's Test Kitchen, and it's really interesting, because it's not just Parmesan sprinkled on asparagus and roasted, which is delicious on its own.

For this recipe we use ground-up Parmesan, panko bread crumbs, a little bit of butter, and then we whip egg whites, so the crust we're creating on these roasted asparagus spears is a little bit lighter and airier, but still with that like crispy, nutty, Parmesan crust.

 SS: Sounds delicious. Do you save the rind from the parmesan and use it?

MB: I always save the rind. I love to stick it in soups and stews and give them that kind of nutty, parmesan flavor.

SS: It's precious stuff.

MB: Waste nothing.

Courtesy of America's Test Kitchen

America's Test Kitchen
The Splendid Table frequently visits with the test cooks at America’s Test Kitchen to discuss a wide range of topics including recipes, ingredients, techniques and kitchen equipment.