A year ago, high-end steak houses were screaming for USDA Prime. And then came the recession and a sudden shift away from luxurious dining. The resulting glut of prime beef was now being dumped into the retail sector, said Savell, the chair of the Meat Science section. (Fill your freezer while it lasts.)

Meanwhile, fajitas are in short supply. In 1988, the U.S.-Japan Beef and Citrus Agreement reclassified outside skirt, the cut that started the fajita craze, as tariff-free offal. The Japanese, who used to pay the equivalent of a 200 percent tariff on U.S. beef, now buy our outside skirt steak with no tariff at all. They are currently importing 90 percent of it.

Fajitas are the heart of modern Tex-Mex. They became popular when consumers started rejecting cheesy combination plates in the 1970s and 1980s in favor of more authentic Mexican cuisine. The name "fajitas," along with the recipe and the service style, came from the Lower Rio Grande Valley of Texas, not Mexico. But at least it was authentic Tejano cooking. The name fajita means "little belt" and refers to the shape of the outside skirt — anything else isn't really a fajita.

With outside skirt in short supply, Texas meat companies have compensated by offering some new fajita cuts to restaurants. In fact, the Texas A&M Meat Science section is working on fajita replacements. The meat doctors started rhapsodizing about wedges, flaps, hangers and tails. At the time, it sounded like they were discussing airplane parts.

"What kind of meat do you use in your fajitas?" I asked the restaurant manager at Papa Perez when he stopped by our table.

"We use inside skirt steak," he said. "It's already marinated when we buy it. Then we add our own seasonings."

"It sure doesn't get this tender when I grill it," I said.

Then the meat doctors shared a secret — enzymes. To create tender beef fajitas like the ones on our sizzling comal, meat processors treat tough inner skirt with commercial enzymes or natural enzymes such as papain, which is extracted from papaya, and ficin, which comes from figs.

Papain is tricky. It doesn't start softening up the meat until it is activated by a temperature of at least 122 degrees F. And once it starts, it doesn't stop until the meat cools off. If you have ever had fajitas that tasted like mush, it's because they were cooked too long or the restaurant kept papain-treated meat in the warmer or on the steam table too long after it was cooked.

But you can get papain in the grocery store — it's the active ingredient in Adolph's Meat Tenderizer. All I had to do was come up with some marinade recipes with papain, and backyard barbecuers could make tender inside skirt steak at home, right?

Savell and Griffin said it's not that simple. When you marinate meat at home, you are lucky to get a 2 percent "take-up rate," as the measure of absorption is known in the biz. To increase the take-up rate, commercial meat packers do their marinating in a commercial vacuum tumbler. Mechanically tumbling the meat and the marinade in a rotating vacuum container with paddles breaks up and stretches out the protein fibers, increasing the meat's ability to absorb the liquid.

With as little as 20 minutes of vacuum tumbling, the "take-up" ratio can be increased to 10 percent. Along with the tenderizer and spices, salt and phosphate are also added to increase moisture retention. That makes the meat juicier and pads the meat packers' profits by increasing the weight.

But it gets even more complicated. There isn't enough inside skirt steak to satisfy the demand for fajitas. And so the meat scientists are experimenting with other cuts. These mechanically tumbled, enzyme-treated meat cuts are all sold interchangeably under the umbrella term "beef for fajitas." You can sample this faux fajita meat at any taqueria in town.

But marketing mystery meats under generic names like "beef for fajitas" runs counter to everything that's going on in the food world. It's exactly the kind of deceptive marketing Eric Schlosser takes on in the new movie Food, Inc.

The local-food movement has impressed consumers with the importance of provenance. And meat is the next big thing. That's why so many urbanites nationwide are signing up for butchery classes. Food lovers are ordering organ meat at restaurants, looking for short ribs and soup bones at the grocery store, and trying to cure their own bacon at home.

At Tom Mylan's hugely popular butchery classes at the Brooklyn Kitchen in New York, home butchers are learning how to cut up a side of beef, a whole hog or a lamb. At a meat market in San Francisco, chef Tia Harrison teaches a hands-on class in meat-cutting techniques for women.