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The Clay Mystique

The Clay Mystique

A gastro-scientific investigation into why cooks believe food tastes better (note: much better) when it’s cooked in a ceramic pot. Tour guide: Paula Wolfert, the legendary queen of American clay-pot cooking.

By TODD OPPENHEIMER
Photos by CLAIRE BLOOMBERG

Paula Wolfert | Craftsmanship Magazine, Spring 2015

Paula Wolfert has been writing about her obsession with clay pots for 40 years. She single-handedly brought the Moroccan “tagine” (the dome shaped clay pot to her right) to the American culinary community — a feat that forever crowned her as the queen of clay pot cooking.

Paula Wolfert, now 77 years old, is famous for several things, the first probably for saying this: “I’m not sure how it happened that I became a clay pot ‘junkie.’ At age 19, I bought my first, a potbellied tripiere, used for cooking tripe…” When telling this tale, which Wolfert has done many times, she goes on to say that, at the time, she didn’t even know what tripe was, and chose the vessel simply for its good looks. Forty-eight years later she still can’t kick the habit. While traveling throughout the Old World, from Morocco and Turkey to Italy and France, Wolfert has collected hundreds of ceramic pots, each one possessing a slightly different clay material, shape, size, purpose, and cultural history. In many cases, Wolfert just fell for good looks again; but in most cases, there were slight differences in what each pot could do to food—all of them delicious.

Exactly how these differences happen has bedeviled Wolfert and other food experts for a very long time. Some of the reasons are simple, while some remain beyond the perceptions of modern science. Which is a remarkable fact, considering the thousands of years that the human species has been making and cooking in these vessels. For her part, Wolfert has written 9 food books related to her efforts to understand the magic in this culinary tradition, which for some reason the West has largely abandoned.

Unglazed tagine, a favorite of Paula Wolfert | Craftsmanship Magazine

An unglazed tagine, Wolfert’s favorite style of clay pot (if you press her to choose one).

In one of her more recent books, Mediterranean Clay Pot Cooking, Wolfert tried to summarize what she’d learned and what questions remained. “I begin this book,” she wrote, “by asserting a simple truth: Most food—and Mediterranean food in particular—tastes better cooked in clay.” From all indications, virtually every chef who has ever tried clay agrees. But what is different. And why?

To parse this out, let’s begin with the obvious, then move into the invisible.

Paula Wolfert's collection | Craftsmanship Magazine

As you can see, choosing a favorite among her clay pot collection is not exactly her forte.

The truest (or at least oldest) form of clay-pot cooking is done in unglazed clay, which allows both the material and its pores work their magic. Like organic food, Wolfert wrote, “unglazed clay vessels are organic since clay is a form of the earth.” And this gives the food “a taste and aroma I define as ‘earthy.’” (Wolfert particularly notices these flavors when cooking heirloom beans. We will get into the subject of beans in a moment. In the meantime, for Wolfert’s quick synthesis of the various competing philosophies about how to prepare beans, see our sidebar, “Beans: To soak or salt — that is the question.”)


In one of many tales from her travels, Wolfert says a Turkish cook insisted that her guvec had a kind of “memory” of the dishes she always cooked inside it. When she relayed this tale, it reminded a Turkish friend of a local saying: “If a clay pot recognizes an old tenant, it will produce a delicious dish when you bring the pot back to life.”

As the pot is used again and again, and those flavors accumulate in clay’s microscopic air pockets, “the deeper and more delicious the food cooked in it tastes.”

Many food experts, and particularly food scientists, are skeptical about the flavoring effects of clay as a material (after all, once it’s fired, clay is considered relatively inert). Try telling that to Wolfert’s crowd, many of whom come from cultures that almost revolve around such lore. Take the Turkish “guvec,” a pot shaped very much like any other, except that it’s made of thick clay. In one of many tales from her travels, Wolfert says a Turkish cook insisted that her guvec had a kind of  “memory” of the dishes she always cooked inside it. When she relayed this tale, it reminded a Turkish friend of a local saying: “If a clay pot recognizes an old tenant, it will produce a delicious dish when you bring the pot back to life.”

A French daubiere made by Philippe Beltrando | Craftsmanship Magazine

One of the tagine’s main competitors, at least in Wolfert’s kitchen, is the French daubiere. This beauty, made by Philippe Beltrando, is made of 3-4 different kinds of clay — to get the perfect blend of earthy tastes, heating capacities, and strength.

Farther north, in Marseilles, France, Wolfert continued her questions with Philippe Beltrando, a master potter who makes a snowman-shaped French stewing vessel called a “daubière.” (For Paula’s exegesis of this vessel’s unusual powers, please read our sidebar, “The Magic of the French Daubière.“)

“Maybe someday scientists will come up with an explanation,” Beltrando told her. He said he suspected it had to do with clay’s “even diffusion of heat” which he described as “soft heat that creates great alchemy in the kitchen.”

Romantic stuff, descriptions like these. And they get better. Wolfert goes so far as to say that clay pots “coddle” food, bringing out “bright, natural flavors” and “an unctuous tenderness.” It turns out there is a scientific reason that something as simple as clay moves cooks to wax so poetical.

American potters and "flameware" | Craftsmanship Magazine

On the other end of the ceramic cooking spectrum are pots made from sophisticated composites of clay, boron, silica, and other materials. The combination, called “flameware,” becomes almost indestructible after being fired in high-temperature kilns. Travis McFlynn, a potter in Oakland, Calif., makes a form of this pottery that is slightly porous — a rare quality in flameware.

Now that it’s time for the invisible, let’s take a moment to remember our high school science classes. Some of the mystery revolves around a few basic principles of physics—particularly the differences between materials that are conductors and those that are insulators, and how the laws of thermodynamics react to each one. Metal is an unusually intense conductor, which means that it gathers heat quickly. Clay is exactly the opposite. It’s an insulator—so much so, in fact, that ceramics are used as coverings to keep people and objects near them from burning. So why would anyone use an insulator for cooking?


Metal is an unusually intense conductor, which means that it absorbs heat’s energy fast, like a rambunctious teenager, and then releases it fast. Clay is the exact opposite. It’s an insulator; like a patient grandmother, it gathers energy slowly—and releases it just as slowly.

The reason is like that old cliché about money: Easy come, easy go. Conductors absorb heat’s energy fast, like a rambunctious teenager, and they release it fast. Insulators gather the energy slowly—almost reluctantly, like a patient grandmother—and release it just as slowly. Why does this matter? Consider what’s been learned lately about “low and slow cooking,” especially regarding meat.

When you cook a steak in a hot skillet, it gets a nice char but it also gets tough—because the muscle tissues in the meat seize up from the sudden shock. This is what has led to all of the experimenting recently with techniques such as “sous vide” (cooking meat forever in a sealed plastic bag at temperatures far below boiling) or the “reverse sear” in BBQ, where meats start somewhere between 225 and 250 degrees; then, hours later, go back to a hot grill, just for a moment, for browning. Advantageous or not, these are fussy routines. A clay pot will do much of this work for you, and without exposing your chicken cutlets to warm plastic for hours on end.

Flameware | Craftsmanship Magazine

McFlynn’s pottery can withstand cooking in commercial ovens that reach 1,000 degrees. It can even go from the freezer to the stove, without seeming to notice the shock; that move would shatter most ceramic cookware. That makes a “cloche” like this one — a  McFlynn prototype — potentially ideal for the home baker.

The curious element in the physics here is that the laws of thermodynamics apply regardless of the temperature. At a high temperature, a clay pot will still cook more slowly, and more gently, than an iron one. And an iron or steel pot will cook more aggressively, even at a low temperature. That dynamic multiplies almost exponentially in a pot lined with aluminum or copper, which are the most conductive of metals. (For a tour of the numerical distinctions here — and my own kitchen experiments with them — see sidebar “The Laws of Thermo-culinary Dynamics.”)


What all of this means is that cooks may be fooling themselves when they think they’re practicing the fine tradition of low and slow cooking with a metal pot, no matter what the temperature.

The funny part of these scientific principles is that primitive cultures seem to have figured them out a long time ago. When I talked to Wolfert about all the differing opinions I gathered from experts on both clay and food science as to whether clay pots heat evenly or not, she was surprised.  Then she told me a story. In many Moroccan villages, it’s the custom to prepare meals a day ahead of time by filling a tall clay pot with meats and seasonings or vegetables, packing them in tightly, covering the pot, and and then leaving it overnight in the ashes of a big communal fire. This would obviously create an exceptionally uneven heat source; yet when the villagers retrieved their pots in the morning, Wolfert said, “The whole thing was cooked perfectly evenly.”

What all of this means is that cooks may fooling themselves when they think they’re practicing the finest tradition of low and slow cooking by putting food in a metal pot and then setting the oven at around 250 degrees. No wonder the Slow Food movement drew its inspiration from the old days in Europe, where clay-pot cooking was the norm. As Wolfert herself discovered when interviewing both chefs and home cooks around the Mediterranean, most “still prefer these traditional cooking vessels to the new, flashier metal alternatives. Whenever I asked why, I got pretty much the same set of answers: Clay pots produce tender, juicier, tastier meat without basting and often with less fat; they heat evenly; they retain moisture so the food remains succulent.”

If clay has such a dramatic effect on meat, what about beans and vegetables? More than likely, plants enjoy the gentle touch just as much as a slab of animal. In the case of beans, clay’s powers—in contrast to metal—might go beyond that. For Felipe Ortega, a master potter in New Mexico, the difference is so dramatic that he hated beans before he got a chance to taste them cooked in clay; now, he’s devoted his life to making clay pots, many of them designed especially for beans. (See “The Clay Conjurer,” by Deborah Busemeyer.)

To get a glimpse at what might be going on here, think about when you last cooked beans in a stainless steel pot. Did you notice the cloudy marks the beans left on the bottom of the pot? Do you recall that they don’t come out with normal soap and water, even with a scrubby? (The only way I’ve found to remove them is with a special cleaning powder, such as Bon Ami or Barkeeper’s Friend.) Something is getting created here that is not solely from the beans. And my guess is that it comes from the chromium in stainless steel, which forms an oxide on the implement’s surface to keep it stainless.This is why one chef in Turkey gets very protective of his clay pottery–a tale Wolfert recounts in our sidebar, “The delightful history of the Turkish Guvec.”

Chad Robertson of Tartine Bakery fame | Craftsmanship Magazine

Chad Robertson, the now legendary founder and co-owner of Tartine Bakery, has been working with McFlynn to perfect his cloche design. One of the main challenges in home baking is to create a crispy crust the way professionals like Robertson do. The task is virtually impossible in a home oven, but if the dough can be baked inside a cloche--or some other vessel that can be covered and pre-heated to about 500 degrees--perfection is at least within reach.

It’s only a hunch, and the well-known food scientist Harold McGee believes I am wrong. McGee is also skeptical of many of the claims made by clay pot lovers, who he thinks are swayed by the pottery’s beauty and sentimental back-stories. “Clay pots are beautiful things to hold,” he told me. “And that inspires people to get a little romantic about their capacities.” He even doubts that clayware’s shapes—which tend to be rounded, while metal pots almost universally have straight sides—make much difference. “I doubt that the vapor circulation in a curved-side pot is very different or is significant,” McGee said in an email to me. “The fit of lid to pot is the main factor. Maybe juices get more concentrated in a clay pot because the lids aren’t that tight, so a lot of steam escapes.” Overall, he said, “My general feeling is that these supposed effects are invoked by clay proponents to tell a convincing story as to why clay is better, on the basis of little or no actual evidence.”

McGee’s arguments stun Wolfert, particularly his contention that shape doesn’t matter. “Of course it does,” she says. “Oh, my God!” As proof, Wolfert pointed to scores of highly regarded cooks who are very particular about which shape pot should be used for any given dish. In fact, when she looks at an old pot from Morocco or Italy or Mexico, Wolfert can quickly tell you exactly what dishes this pot has cooked, and which ones it should. As proof, just look at her recipe for Italian fava bean soup.

A cloche for home use | Craftsmanship Magazine

John Pelka, an avid home baker in San Francisco, gives Robertson a little feedback based on what he looks for in a cloche. For Pelka, a cloche’s bottom half should have a gentle curve — the better to cradle the dough as it bakes. This also ensures a rounded crust, just in case a baker gets sloppy and lets his dough spill toward the vessel’s edges.

Todd Oppenheimer is founding editor and publisher of CRAFTSMANSHIP. Claire Bloomberg is a photographer based in the San Francisco Bay Area who specializes in food.

If you are interested in purchasing some clay pot cookware, a store in Wolfert’s hometown of Sonoma, California called Bram Cookware offers a wide selection — Moroccan tajines, Spanish cazuelas, Colombian black La Chambas, and yes, Egyptian brams. For a daubière by Philippe Beltrando, look at Barbara Wilde’s online store on French gardening. Although located in France, Wilde offers international shipments of Beltrando’s daubières, poêlons, mortars, and other clay pots. Travis McFlynn’s “flameware” can be found through his shop in Oakland, saramc. One of Wolfert’s favorite sources for flameware is Clay Coyote.

© 2017 Todd Oppenheimer, all rights reserved. Under exclusive license to Craftsmanship, LLC. Unauthorized copying or republication of this article is prohibited by law.

Published: April 30, 2015

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