Dollar sales in the Mexican restaurant segment were up almost 8 percent between 2006 and 2007, according to Chicago-based research group Technomic Information Services' Digital Resource Library. Both limited- and full-service Mexican restaurant sales totaled more than $18 billion in 2007. Total units also showed about 4-percent growth in this category.

What is remarkable is how this cuisine has evolved in recent years. Although the more traditional dishes, such as tacos, burritos and the hybrid Tex-Mex, continue to draw diners, there has been an influx of regional recipes using healthy, authentic ingredients native to Mexico. Along with cheddar cheese, ground beef and picante salsa, today's restaurants offer queso cheese, fresh seafood and mole sauce.

Many say this trend mirrors the evolution of Italian food, which first became popular as spaghetti and meatballs, before transcending into more sophisticated dishes reflecting Northern and Southern Italian regions.

The demographics continue to shift, as well. Long a staple in U.S. states bordering Mexico, such as Texas and California, Mexican food is becoming more widespread in the Northeast and rural Midwestern and Western states.

One of the most notable success stories in this segment's limited-service restaurant category is Denver-based Chipotle Mexican Grill. Just 15 years after its first location opened, the fast-casual chain now has 775 locations throughout the country.

This is an increase from 670 sites, according to Technomic, which reports that the chain's 2007 sales totaled more than $1 billion.

According to Jim Adams, executive director of public relations, the menu has remained pretty much the same since the chain's inception. “The only change is the addition of salads a few years ago. Currently, we are trying to improve our ingredients and have made a lot of strides in that regard,” he says.

Chipotle's menu is geared around large, customized burritos. These are prepared in a production line setup using 17 ingredients that customers can mix and match.

Its focus on quality ingredients includes naturally raised pork and chicken, RBGH-free cheese and sour cream and organic beans. More than 50 percent of its beef also is naturally raised.

The chain's kitchen is as simple as its menu. Grills are used for preparing meat, while beans and shredded meat are heated on a stove top. Prep items include knives, mixing bowls and cutting boards. The front line includes a tortilla press, rice maker and warming and cooling bins that hold ingredients. “We have streamlined and simplified our operations,” Adams says.

Like Chipotle, Qdoba Mexican Grill's menu centers on its large, signature burritos. Staff create these using fresh ingredients with a combination of sauces, salsas and marinades. Flavors include poblano pesto, fajita ranchero and ancho chile barbecue. The menu also includes grilled quesadillas, taco salads, nachos, Naked Burritos, tacos and soup.

The first Qdoba Mexican Grill opened in Denver in 1995, and the fast-casual chain now has 448 restaurants located in more than 40 states. In 2003, Qdoba was acquired by San Diego-based Jack in the Box. The chain's U.S. sales were close to $400 million in 2007, according to Technomic.

Ted Stoner, director of strategic product development, says recent trends in the Mexican food segment have shifted toward more regional flavors, rather than the Tex-Mex Taco Bell-type of offerings. “Our biggest challenge is changing the way people think about Mexican food. There is a stereotype in terms of quality and value, so it can be difficult convincing consumers to raise their expectations,” he says.

Similar to the upscale movement of Italian and Chinese fare years ago, Mexican food is becoming gourmet. Chefs like Rick Bayless of Chicago's Frontera Grill and Modern Mexican Group's Richard Sandoval are helping to transform this category.

Qdoba has had successful growth in the Northeast and in states like Idaho and Montana, which have been slower to embrace regional Mexican fare. “Aside from Mexican food chains and traditional mom-and-pop restaurants, these areas haven't had access to fresh, authentic Mexican cuisine. They have a hunger for it,” Stoner says.

Despite the growing interest, Stoner predicts the adaptation will be slow. “There will still be quesadillas and tacos, but these items will have signature flavor profiles that will bring them one step closer to authentic Mexican,” he says.

The segment is being held back, due to the difficulty in sourcing necessary ingredients. “However, as acceptability grows in this country, there will be more innovative dishes and these authentic ingredients will be easier to come by,” Stoner says.

That's good news for Qdoba, since its menu offers moles and sauces specific to regions in Mexico as opposed to the more Americanized picante and pico de gallo.

Like Chipotle, the chain's entrées are prepared in front of customers who select their ingredients.

The chain runs limited-time offers, such as a grilled chicken mango salad during the summer. “Salads are a good point of differentiation for us. Because our food has a healthy profile, adding these items made sense,” Stoner says.

Lean shredded pork was added to the ingredient list about three years ago, as well.

Because its research showed Americans had less than stellar experiences with traditional mole sauce, Qdoba tweaked its formulation, creating a well-received barbecue version that it serves with chicken and pork dishes.

A new Mexican Gumbo entrée evolved from a northern Colorado franchisee's recipe. It features a burrito topped with tortilla soup. “This dish scored well with our consumer panels and focus groups,” Stoner says. “When we first rolled it out, our guest surveys revealed this dish as one of our most popular menu items.”

As Qdoba's concept is true to authentic Mexican cuisine, its dishes require extensive prep work prior to time of service. Consequently, pork and beef are slow-roasted for six hours, before being hand-shredded. Steak and chicken are marinated, then grilled to order. Dried beans, which arrive in 50-lb. sacks, are boiled in stockpots and seasoned with lime juice, cumin and other ingredients.

Even though the emphasis is on authenticity, Stoner says Qdoba is always on the lookout for more efficient ways to accomplish necessary tasks. Most recently, the chain moved away from cooling its beans in 60-qt. pots with frozen ice wands. “Now prepared beans are put inside bags, which are cooled down under ice. Everything in the bag is ready to go,” he says.

Fortunately, Stoner sees more equipment geared toward producing Mexican food. “There is more specialized equipment available that works better for these products,” he says. “We may look into incorporating these units in the future.”

Currently, Qdoba's kitchens include simple, straightforward equipment. Instead of microwaves, steam kettles and automatic can openers, there are conventional ovens for slow-roasting meats and stove tops to cook beans. “There is a lot of hand mashing to make guacamole. We also have simple fryers to prepare our taco shells, taco salad bowls and chips,” Stoner notes.

Since menu items mainly incorporate fresh ingredients, minimal freezer space is only needed to house frozen cookies. About 25 percent of walk-in refrigeration space is allocated to meats, 50 percent to fresh produce and the remainder to tortillas and similar items.

A tortilla steamer heats large burritos, while a separate rethermalizing steamer warms up Qdoba's signature sauces and tortilla soup.

In the past, the chain used rice cookers similar to those in Japanese restaurants. “These made massive quantities of rice, but we discovered that we didn't always need large amounts. Now, we're testing a new format that uses the retherm steamer to cook single pans of rice,” Stoner says.

Kitchens also include marination stations, in addition to both three-compartment and prep sinks.

Along with its restaurants, Qdoba's catering operation has seen successful growth. “Lunch sales are maxed out in some of our urban sites, so catering helps drive additional revenue at these locations,” Stoner says.

Another leader in the Mexican food segment, Abuelo's was listed in Restaurants & Institutions' “Top 400 Sales Growth Leaders” annual ranking, and is owned and operated by Food Concepts International of Lubbock, Texas. Abuelo's operates 40 locations in 15 states throughout the United States.

Abuelo's is Spanish for “grandfather” or “respected elder statesman,” so it's only appropriate that the hand-carved statues in this Texas chain's dining rooms represent respected leaders and important figures in Mexican history.

The chain's founders James Young and Chuck Anderson opened the first Abuelo's location in Amarillo, Texas, back in 1989, following a trip to Mexico. Their goal was to create an authentic Mexican experience in the United States that blended the art and ambience of their travel experience with culinary creativity.

According to Dirk Rambo, Abuelo's COO, today's economic climate has been a challenge. “Most Mexican restaurants are trying to drive traffic and repeat business as well as attract new customers through value perception and creative offerings. Everyone is trying to fight the battle,” he says.

Restaurant interiors are designed as open-air Mexican courtyards, replicating Mexican-style service. Life-size statues, paintings, greenery and a central water fountain surround diners, creating a serene environment.

Its menu, like the décor, caters to discriminating diners. Abuelo's dishes combine authentic standards with the rich, subtle flavors of both coastal and interior Mexican cuisine.

“One of our most popular dishes is the Pescado Guerrero. This is grilled mahi mahi topped with a scallop and shrimp white wine sauce, spinach, roasted red chiles and mushrooms served with sliced avocado. Another signature dish is Los Mejores De La Casa, which is bacon-wrapped tenderloin fillets and bacon-wrapped shrimp stuffed with fresh jalapeño and blended cheese,” Rambo says.

Its enchiladas are another customer favorite. Diners can choose from avocado, spinach, cheese, ground beef, chicken and shredded beef varieties topped with a choice of sauce.

Abuelo's patrons are first served light and crispy tortilla chips, complemented by two spicy salsas made fresh throughout the day. There is a milder blend called Salsa Infierno, a mix of tomato, onion, pepper, cilantro, herbs and spices.

The menu includes a variety of starter plates, such as Abuelo's Dip Sampler. The three dips include Queso Diablo, a rich, spicy combination of traditional Mexican cheeses and chili; Chile con Queso; and Avocado Cream.

Main dishes give diners a choice of exploring the interior of Mexico or venturing along the coast. Those who prefer the hearty flavors of interior Mexico can choose from a selection of chicken and steak dishes, including Sautéed Chicken Zucchini, a lightly sautéed chicken breast with sliced zucchini, roasted red peppers and corn in a spicy cream sauce.

For those who prefer seafood, Abuelo's offers dishes that include tilapia, mahi mahi, salmon and scallops of the Mexican coastline. One popular dish is Chile Manzanillo, crab imperial stuffed in a roasted poblano pepper with creamy shrimp, scallop and lobster sauce.

Side dishes include Papas con Chile, a mashed potato casserole derived from an old family recipe, that includes a creamy mixture of new red potatoes, peppers and spices, and Frijoles Charros made from fresh Mexican pinto beans, seasoned with jalapeño, onions and cilantro.

Abuelo's menu includes traditional Mexican dishes, as well. These include the aforementioned enchilada choices, wood-grilled fajitas, tacos, chile rellenos, quesadillas, chimichangas and tamales, as well as Abuelo's Mexican rice, made with diced chiles and corn, and refried Mexican pinto beans.

The dessert menu also is diverse. The chain's award-winning Traditional Mexican Flan is made with Mexican egg custard. Other selections include Dulce de Leche Cheesecake with Mexican caramel and leche quemada, a sweetened milk sauce.

Though Abuelo's runs scratch kitchens, Rambo says the chain has recently begun incorporating cook-chill techniques to better control waste and offer fresher product. “As a scratch kitchen, we cook sauces, fillings, toppings and meat twice a day in the mornings and afternoons. We've gone to cooking and bagging these items, going through rapid chill and reheat for evening runs to control production and waste. It also allows us to provide fresher products that don't need to be held heated for four hours,” he explains.

On the production side, Abuelo's does not utilize high-tech equipment. Most of the cooking is accomplished with ovens and high-heat ranges. “We cook in large capacities, using 20-, 40- and 60-qt. pots and double boilers,” Rambo notes.

Staff heat tamales in regular steamers. The chain tested using steam-jacketed kettles for the task, but they weren't as efficient or fast.

A bank of three fryers has low-depth tanks and auto filtration for producing chips, breaded items, chimichangas and rellenos.

Production and prep is completed in the morning using slicers, wand mixers and large blenders for salsa. “Then we have the line build throughout the day. This is where staff take orders as they are placed. Each enchilada is hand-rolled, salads are prepared and tacos are made by initial builders using ingredients from custom-built hot and cold food wells,” Rambo says.

Eight-burner ranges handle the sauté work, while flat-top grills heat up the tortillas. “We do a lot of grill work off the broiler and sauté line,” Rambo says.

Employees add the sauce and cheese, before incorporating the side dishes. Plated food is then baked off in a conveyor oven at 425°F. for about four minutes.

“When dishes come out of the oven, the meal on the plate is baked. This process gives us great heat retention at the table,” Rambo explains. After plates are removed from the oven, a second person garnishes them with guacamole, rice and other cold components.

Another ticket is received at the grill station that provides preparation instructions for these items. Abuelo's is currently using wood-fired grills, but has begun testing charbroilers with wood trays. “We are finding that charbroilers are more space-efficient, offer easier temperature control, operate cleaner and are less costly to use,” Rambo says, adding that the test is going well. “We anticipate including charbroilers at our new locations.”

Walk-in refrigerators have three separate compartments, each with its own door, for produce, meat and dairy and frozen items. Hot boxes also are used for storage.

Abuelo's has slowed its growth, due to the current economy, opening two stores this year and two in 2009. “We will begin scaling up, adding sites when the economy improves,” Rambo says.