Written by TODD OPPENHEIMER
Photography by CLAIRE BLOOMBERG

Paula Wolfert, 77 years old at the time of this writing, 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. Fifty-eight years later, she still can’t kick the clay-pot 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 nine food books related to her efforts to understand the magic in this culinary tradition, which for some reason the West has largely abandoned.

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 cooking in clay agrees. But what is different? And why?

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

COOKING IN EARTH

The truest (or at least oldest) form of clay-pot cooking is done in unglazed clay, which allows both the material and its pores to 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 to Salt — That Is the Question.”)

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 clay’s lore. Take the Turkish güveç, 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 güveç had a “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.”

Farther north, in Marseilles, France, Wolfert continued her questions with Philippe Beltrando, a master potter who makes a snowman-shaped stewing vessel called a daubière. (For Paula’s exegesis of this vessel’s unusual powers, please see 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.

FLAVOR’S MIDWIVES

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.

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?

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 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 F.; 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.

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 our sidebar, “The Laws of Thermo-Culinary Dynamics.”)

The funny part of these scientific principles is that ancient 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 be 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 F. 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 master potter Felipe Ortega, the difference was so dramatic that he always hated beans until he got a chance to taste them cooked in clay. Afterward, he devoted his life to making clay pots, many of them designed especially for beans. [See Craftsmanship‘s story, “The Clay Conjurer.”)

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 Güveç.”

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 was designed to cook. As proof, just look at her recipe here for Italian fava bean soup.

Resources for Clay Pot Cookware

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 tagines, Spanish cazuelas, Colombian black La Chambas, and yes, Egyptian brams. For a daubière by Philippe Beltrando, look at Barbara Wilde’s online store. Although located in France, Wilde offers international shipments of Beltrando’s daubières, poêlons, mortars, and other clay pots. One of Wolfert’s favorite sources for flameware is Clay Coyote.