THE BLOG
10/11/2013 03:46 pm ET Updated Jan 23, 2014

If Walnuts Are So Good for Us, Why Is Eating Them a Crime Against Nature?

Those walnut bits in your brownie. Those walnut halves on your salad:

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They didn't just land there after floating through the air obligingly. Oh, you knew that. "Walnuts," you retort, "come in hard, heavy, eyeball-sized, sand-colored, smoothly wrinkled shells the shape of swollen hearts."

True. They do. But those hard brown shells aren't what you'd see hanging from walnut trees. In real life, on the branch, walnut shells are sheathed in leathery green hulls, as if trying to disguise themselves as avocadoes.

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Most of us go our whole walnut-eating lives without ever knowing this. Or knowing that at the very brink of harvest time -- e.g., right this minute, at least in California, which produces 99 percent of the walnuts sold commercially nationwide -- these green hulls split while still in the trees, baring the familiar brown shells.

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I might never have known this either, despite having been born and raised in the walnut capital of the world, had I not watched the harvest in action last week at Alpine Pacific Nut Company near Ceres, CA.

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Their long-reaching, lissome boughs rising from short thick trunks, the trees baked under a blastingly hot sun like orderly rows of anguished poets wailing with upraised arms, Why?

And well they might. Because a philosophical question kept dogging me during my orchard visit, courtesy of the California Walnut Board: If walnuts are so delicious and nutritious -- recent studies link walnut consumption with improved heart health and reduced prostate-cancer risk -- then why are they so hard to crack?

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You might say the same thing about oysters. But nature hides each creamy-tender brain-shaped walnut meat within not one but four consecutive layers of protection: papery bitter skins. Fibrous membrane. Hard shell. Leathery sheath. Archeological evidence suggests that human beings have eaten walnuts since at least the Holocene era: How did our prehistoric ancestors deduce what was inside all those layers, which might make it worth banging away at them with rocks?

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Sure, nut meats are a more passive protein source than, say, antelopes. But they're still startlingly user-unfriendly. Even -- as I saw firsthand in that orchard -- for us. Other things we can just pick from trees and pop straight into our mouths. Why are nuts so uniquely hidden, shielded, guarded like the treasure within the fortress within the fortress within the fortress within the fortress in some fantasy scenario? It's as if the universe didn't want us to know about walnuts at all. It's as if cracking and eating them was a crime against nature.

Later, an expert would unravel this mystery for me. But first, I watched an industrial shaking machine roaring up and down between the rows of trees.

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To wrestle tons of nuts from thousands of trees quickly enough to clean and dry them before the meats inside start to mold, big growers such as Alpine Pacific -- which produces some 20,000 tons per year, supplying Costco and other huge companies worldwide -- use mechanical shakers that seize boughs between their massive vibrating "jaws" to send nuts hailing earthward, sounding like an all-castanet orchestra.

The nuts are then swept up by other machines and trucked to hulling-dehydrating facilities such as the one owned by the Keyes Road company in Turlock, CA, where they undergo various procedures to sort, clean and dry them, such as this:

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And this:

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Then they travel to bulk storage and shelling facilities and are sold. Then they go into treats such as this exquisitely velvety walnut soup, created in honor of the walnut harvest by chef Mark Berkner and chef de cuisine James Ablett (who also created the salad depicted above) at Zagat-rated Taste Restaurant in Plymouth, CA ...

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... and this heavenly caramelized-walnut ice cream, depicted alongside a fruit-nut tart and created in the seasonal spirit by chef-owner Randall Selland and chef John Griffiths at Sacramento's also-Zagat-rated The Kitchen restaurant:

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I put my crime-against-nature question to evolution expert Kristan Lawson, author of the award-winning book Darwin and Evolution for Kids.

"When we think of walnuts," Lawson said, "we think of them as something to eat -- whether it's squirrels storing them for winter or us attacking them with nutcrackers.

"But walnuts do not exist for the purpose of being eaten. They exist for the purpose of propagating future walnut trees. So just as a herd of adult elephants will surround a baby elephant to guard it from the lions that want to eat it, a walnut tree correctly regards every walnut hanging from its branches as its baby, needing protection from predators.

"Thus the walnut shell and its thick green covering are the protection that keeps a 'baby walnut tree' alive long enough to make more walnut trees. The delicious meat nourishes the germ as it grows on the branch -- comparable to the yolk in an egg."

Wait -- so walnuts don't propagate like this?

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"Trees require very large seeds, because trees are very large organisms," Lawson explained. "Smaller plants such as poppies have such numerous, tiny seeds that they don't need this kind of protection. In nature they just fall undetected, safely, to the earth. Nuts are the seeds of nut trees, and they uniquely need shells.

"It's all about survival of the fittest. Over the millennia, the trees that have been the most successful in nature have been those whose seeds had the hardest, biggest and most protective shells.

"If walnuts had no shells, if their delicious meats just hung on branches unprotected, they would all be gobbled up effortlessly by every passing creature. If that was the case, no walnut meats would survive long enough to reach the ground, germinate and sprout into new trees. If that was the case, walnuts would have become extinct long ago."

In other words: Love the hull. Thank the shell.

Photographs by Anneli Rufus.

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