He does this to concentrate the flavors, and he does this because it's a torta and if you order a sandwich and the filling has toppled out and the bread slid from its foundation, you wouldn't think highly of your torta. He does this gently and though he does it without a word, he does it with more intensity and irritation than he has all afternoon. You would have to watch closely, for many hours, before noticing the slightest sign of a fissure in his bright, energetic composure. Nonetheless, it is happening.

Rick Bayless is starting to fray.

"No, no," he says to himself, pressing another torta together.

Things are unraveling.

It is 2:35 p.m. on a Thursday. The line at his new restaurant, Xoco, which is committed to Mexican street food, is out of the door and down Illinois Street. At 3 p.m., the menu will switch from tortas and Mexican snacks to caldos, or soups, which means the assembly line of cooks behind the counter needs to prepare for the switch, which means doing things they don't have time to do because the line is not easing. Which means tortas are starting to come out wrong, and the floor behind the counter is getting dirty. Despite their ubiquitous mutter of "Behind you," cooks are banging into one another. A chef from Bayless' Frontera Grill, next door, wants to assure him that new pans were ordered. A television crew from WGN stops by. A reporter from Univision wants to talk. Then a photographer from Zagat.

He looks dizzy.

So, without a word, Bayless wipes his hands on his apron and abandons his post alongside his cooks, most of whom are not that used to having the boss, let alone a celebrity chef who draws intent stares from customers, cooking alongside them all day.

Bayless walks with his head down through a side door connecting Xoco with Frontera Grill, his first restaurant, which opened in 1987 and eventually spun off a line of jarred salsas, a cookbook empire, a PBS series, etc. There, his wife, Deann, is sitting at the bar with his longtime manager, Jen Fite. He says they are stopping. For maybe 15 minutes. Just to reboot. "It's tenuous over there!" he says in a harsh whisper. Heads crane in his direction. Then, softer, he says: "This is the first time since opening we started serving crap! I'm letting crap clear that counter. Because we cannot keep up."

Deann says no, you are not serving crap.

Fite, who looks stricken, says he should not close, not now; the whole point of the new restaurant is to stay open when the other Bayless restaurants are closed, so customers can get his flavors all day and not just during the lunch and dinner times. He nods. For a long moment, no one speaks.

Then Deann asks: "How much staff do you need to get back to a normal pace?"

"I just don't know."

He turns, walks through the kitchen, rejoins the line, his jaw set, his face hard, and stops serving food for 45 minutes.

Rick Bayless has a cold.

This is the first thing he tells me when we meet, a day earlier -- that he has a cold, and that he has laryngitis, and that he feels terrible, and that he's really sorry I picked this week to shadow him but maybe, you know, now is not the time, that maybe I should come back next week or something. He does not smile when he says this, and he does not say this with any apparent degree of apology, but rather a barely concealed annoyance that I actually showed up. I had planned to be at his side for two days, morning until night, to listen to every conversation, to watch and taste, and see what emerges from the small details and fleeting moments of the daily life of this superstar chef, arguably the most recognizable American chef of the moment. He agreed, but at this moment, a punch to my face seems a more likely emergence. Xoco (pronounced SHO-ko) opened 24 hours earlier, and he bares a look of irritation and anxiety that, friends and associates assure, is rare for him to show in public.

"He has two faces," said Amado Lopez, the night chef at Xoco. "They shot (the PBS series 'Mexico: One Plate at a Time') at Frontera last year. He was low key, then the minute they yelled 'Action!' he got really animated. But that's not phony. The pressure is on when you work in his kitchens. So many people come here just to look at him, or with an idea of him, there is pressure to perform, to give your best face. Everyone feels that. But it's a more subtle pressure than in other kitchens. Other chefs get mad faster. Rick is colder, more subdued. You never see him lose it. I never have."

Bayless is unusual.

Unusual in the unrelenting grin that is his public face. Unusual in that he built an empire on Mexican cuisine, despite growing up in Oklahoma City, the white son of barbecue chefs. Unusual in that few chefs, famous or otherwise, have done years of doctoral work in linguistics (at the University of Michigan). Unusual in that, despite winning both chef and restaurant of the year awards from the James Beard Foundation (then following up with a Beard Humanitarian of the Year Award, in 1998), he decided to endorse a chicken sandwich for Burger King in 2003.

But also, unlike other well-known chefs who have reached his level of respect, his restaurants -- Frontera, Topolobampo, now Xoco -- have stayed financially approachable. And then there's the decision to do "Top Chef Masters." Despite being among a few Chicago restaurateurs still firmly established decades after arriving, he chose to appear on the popular Bravo reality show and risk that reputation before a national audience.

Bayless, 55, said he wondered about that himself, but in the end, it was more important that he keep trying something new, even if he failed. He said he didn't want to become "one of those chefs always making the same thing they made 20 years ago." He said later, "We don't really make a lot of money in this business. It's a hard one too. Hours are long. And the one thing you never have is time. I think for a lot of people who do this, the most meaningful thing becomes their time, and how they spend it."

Hubert Keller, the French chef of San Francisco's Fleur de Lys, who ran neck and neck with Bayless on "Top Chef Masters," said he has known Bayless since 1988, the year they both appeared on Food and Wine magazine's annual Best New Chefs list.

"Rick was the person then that he is today," Keller said. "He is that earnest guy you see. During the show, he suggested I use a pressure cooker for one dish. I said I have never used a pressure cooker. Once the show was over, he sends me a pressure cooker. The thing is, there is little one can hide after you've been in business as long as we've been. Everyone in the industry knows who the good guys are and bad guys are, and what they say about you after so many years is either truth or has become truth."

Bayless is unusual, too, in that, with few bumps over the years, he has gained more than he has lost.

Particularly the last year or so, which began with the Obamas swinging by for a postelection dinner. It continued in the spring when the James Beard Foundation held its nomination ceremony for the first time outside New York and chose Frontera Grill for the location. In August, it was revealed that he won "Top Chef Masters" and $100,000 for the Frontera Farmer Foundation, which he started six years ago to promote sustainability among small farms. By Labor Day, waits at Frontera were stretching as long as four hours -- which hasn't been true in years -- and reservations at Topolobampo required eight weeks' notice. The next day, he opened his first restaurant since 1989. (Frontera Fresco, a fast-casual space in Macy's on State, opened in 2005.) By October, his 140-member staff, in three restaurants, was serving 2,000 people a day.

"Rick makes us all look like underachievers," said Carrie Nahabedian, the chef/owner of Naha, which has been cater-corner from Frontera for nine years. "Despite it all, he has not expanded (outside Chicago) -- if a lot of us get offers to open restaurants across the country, imagine the offers he gets. But he is firm about not prostituting himself. He has learned where to draw the line and he knows better than to jeopardize the future of everything just because of this moment he's going through right now."

Bayless hasn't worked the line in 15 years. Which means he hasn't stood through roughly 12-hour shifts, chopping, washing, arranging -- the day-to-day, dish-to-dish life of a busy kitchen. He tells me, in fact, that he has been less of a presence in the dining room over the years.

"I used to poke my head into the tables more, but servers tell me it slows everything down."

And yet because he hasn't opened a restaurant in a while, and because a lot of people are looking at him now, he decided to camp at Xoco for the week. He places a cloth to his left, a tasting spoon to his right. The spoon stays in this spot for 12 hours; after he uses it, he returns it to its exact spot, every time. He says it's compulsive, "the way kids need to have things exactly where things belong."

A few hours later, Lopez kicks a cook off the line. He thought the guy wasn't organized, that he was slowing everyone down. Bayless sighs. "I think the poor guy was in tears," he says, then returns to his place, glancing at order tickets, slicing bread. He cracks an egg, stands over a pan, shifts the yolk, steps back, flips it with a flick, says "Egg," turns and slides it onto charred toast.

Behind him, Shaw Lash, Xoco's morning and afternoon chef, whom Bayless met on a trip to Mexico, is shifting tortas around the wood-burning oven. Bayless watches and nods, then leaves for the Frontera kitchen. He walks that line, lingering over a bubbling sauce a moment, then moving on. He does this three times a day, tasting, then suggesting, asking a few questions.

As he steps back into Xoco, he is immediately grabbed by a customer, a small, round woman. "I just want to thank you for opening another restaurant and representing my country," she says to Bayless, who steps back, pauses and says, "Thank you."

As Bayless moves on, a young man waiting for food calls after him: "Rick, do you like being a celebrity?"

"No, yes, no, yes," Bayless mumbles to himself.

Back on the line, he leans back against the counter and pulls out an iPhone. He texts his daughter, Lanie, who left the weekend before to start freshman year at New York University. Then he answers a few questions from fans via Twitter -- people forget, but Bayless' promotional streak is so ingrained, his first cookbook came out a month before he opened Frontera. He cooks awhile, then walks back into the Frontera kitchen and finds Brian Enyart and Richard James, chefs de cuisine at Topolobampo and Frontera. He wants to show them something. He walks them over to a new fire door, a bulky metal thing, with steel chains strung along its frame.

"I am horrified by this!" Bayless says, hands at his cheeks. "Have you seen anything so ghetto in all your life? A health code violation? It's terrible. The most ghetto-looking thing I've ever seen."

At 8:30 p.m., a server at Xoco locks the front door and the kitchen stops taking orders, a half-hour before the official closing time. If they don't, Bayless decides, they will be serving food for hours. At 10 p.m., he says, "I'm going home."

We walk through Frontera's kitchen. He says he comes here now for quiet. We talk a little about whether he could ever own the block, because they rent the building now. Not enough capital, Bayless says. Then, apropos of nothing, he tells me he hates sports, and in his breathless style:

"I grew up in a family of people who were and still are wild about sports, and I hated sports. I was always the outcast of the family. I don't know if you know my brother, Skip, a sports writer (formerly of the Tribune). He's on ESPN. Well, my mother is totally into sports and suddenly now I'm OK in my family because I was in a competition and I won. But, see, all the awards I have won are judged my peers and that doesn't really make a difference to my family. All those James Beard awards -- nice, but they don't care. It's all, like, so what? They don't see being in business and being successful is to be competitive. No, now they see the competitive side because it has been acknowledged.

"My mother was thrilled about 'Top Chef.' She said, 'I have gotten calls from all over the country and people can't believe you won.' Thanks, Mom. My mother's neighbor three doors down found out that I was her son and she said, 'When he comes back to visit, could I meet him?' And my mother's husband said to me, 'You would think you were some kind of sports guy or something!'

"See, that's the world I come from. The only people who matter in that world are sports people. But now I'm legitimate. I wasn't legitimate before, no matter what I won. And now I'm legitimate."

The next morning, after breakfast rush subsides, Bayless removes his apron, turns to me and, coughing out the words, says he is going to a doctor. With comedic precision, moments after he leaves, a city crew moves in and erects a large fence strung with a green curtain around the corner of Illinois and Clark streets, obstructing Xoco's front window, where pastry chefs can be seen grinding chocolate beans, a living advertisement for Mexican desserts. Next, large orange barricades are installed. An hour later, Bayless returns. I see him crossing Clark, lower jaw jutted, arms flapping with incredulity. He stalks in, expression frozen.

"Can you believe this?" he says to Andrew McCaughan, his assistant.

"Gone in a week, they said."

"They could have said they were coming."

The Frontera Empire, which has grown large enough to stretch across the tops of the restaurants and through a network of basements and sub-basements beneath, is "almost single-handedly responsible for renovating a stretch of Clark, I think," chef Charlie Trotter told me later. "People forget how seedy it was over there, full of porno shops, before Rick stepped in. He made a difference. But he is incredibly scrupulous."

Indeed, though the restaurant business can be a transient one for rank and file, it's not unusual for staff to stick with Bayless a decade or more. (Deann told me they recently had two employees celebrate their 20th anniversary with Frontera and, as a thank-you, were given a week off with pay and a trip -- anywhere in the world.)

By 11:30 a.m., the line has started another ominous creep out the door, its third in three days of business. Bayless spends 15 minutes chatting with an owner of La Quercia, a popular Iowa-based prosciutto producer. There's a discussion of whether to start takeout. Bayless wants to start. His managing partner, Carlos Alferez (a dead ringer for Howie Mandel), making hot chocolate, turns and disagrees. The issue is left in the air. An hour later, Xoco, overwhelmed, grinds to a halt for the first time.

Bayless turns to McCaughan, his white goatee in a scowl, and says, "We need time to reset."

"I think that's fine," McCaughan replies.

"If we don't we're going to be serving caldo at 5!"

"That's fine."

Nobody speaks again for 20 minutes. They clean, chop, slice.

An hour later, you would never know anything unusual happened. The parade of cell phone cameras begins anew, and Bayless, each time, switches seamlessly from steely to a gosh-golly-gee-do-ya-like-it gush of modesty, then back to steely. Enyart swings by to have Bayless taste a dessert headed for the fall menu at Topolobampo, a yogurt sponge cake. Bayless would like it a bit sweeter. Around 9, Enyart can be seen through the window, headed home. "Check out that guy," Bayless says. "That guy works banker's hours." An hour later, Bayless unties his own apron and neatly folds it in squares, turns to me and says, "OK, I'm heading home." Deann appears. "We have a Skype appointment with our daughter," she says. "And then home," Rick says.

Earlier this year, Bayless' name was thrown around as a possibility for White House chef -- the truth is, as people close to him said, if asked, he couldn't stay away from Clark Street for a presidential term anyway. He prefers a large amount of control over a smaller kingdom. At the moment, as it has been for almost 25 years, his vision remains manageable -- that is, a vision predicated on how much of that vision he can manage without killing himself. He prefers to expand laterally, demographically. "This is the main audience for Bravo and Twitter," he said about Xoco's customers, much younger than the typical diner at Frontera or Topolobampo.

He passes tourists shooting pictures of him through the glass from outside. He walks through the Frontera kitchen and stops a moment to stare at the fire door again, then groans and continues past the sinks, dodging a man with a large pot. He continues through the doors to the dining room, hooks a right and walks the Frontera line once again. He stops and rests an arm on the counter. The line glances up at him, then quickly down, in one motion. "So, sell many 'Top Chef' tasting menus tonight?" Bayless asks no one in particular.

"Um, a few," comes the sarcastic reply, from a line cook who never stops chopping. "Like, I don't know, 90?"