As you’ve no doubt heard—it’s all the rage on Twitter—McDonald’s in/famous McRib is back, again.

But where did it come from? And where does it go when it departs the McDonald’s menu? All in due time.

Like most American kids who grew up in the absence of fine dining, I enjoyed the reincarnations of the McRib. Then I moved to the big city, and went to fancy restaurants, and made friends who could cook. I even met vegetarians; I remember going to the Chicago Diner in college, unaware that it didn’t serve meat (but it’s a diner!) and was shocked to discover as I bit into my sloppy joe that it was… not meat.

It took awhile, but I finally grew accustomed to pseudo-meat. After discovering seitan at Earwax, I even started buying it occasionally when I was living near the Green Grocer on Grand, which sells a fine flavored seitan. And then I had a revelation: it’s just like a McRib. Since then I’ve wondered why McDonald’s even bothers using actual pork for them. Clearly, we have the technology.

Anyway, I mentioned this to Kiah Haslett, a former Trib intern and business reporter at SNL, whom I follow on Twitter. She said that the McRib was invented at her alma mater, the University of Nebraska-Lincoln (this, incidentally, is why I love Twitter). Which, it turns out, is partially true. The McRib can be attributed largely to two men: a meat scientist from Nebraska and a Luxembourg-born, French-trained chef from the Drake Hotel.

The former is Roger Mandigo, a longtime prof at UNL, a recent inductee into the Meat Industry Hall of Fame and an innovator in restructured meat products. Here’s how Mandigo and two co-authors described the general process in a 1995 article, the process which gives us the McRib:

Restructured meat products are commonly manufactured by using lower-valued meat trimmings reduced in size by comminution (flaking, chunking, grinding, chopping or slicing). The comminuted meat mixture is mixed with salt and water to extract salt-soluble proteins. These extracted proteins are critical to produce a “glue” which binds muscle pieces together. These muscle pieces may then be reformed to produce a “meat log” of specific form or shape. The log is then cut into steaks or chops which, when cooked, are similar in appearance and texture to their intact muscle counterparts.

Mandigo explained the principle behind restructured meat products in Food Chains: From Farmyard to Shopping Cart:

“Most people would be extremely unhappy if they were served heart or tongue on a plate,” he observed. “But flaked into a restructured product it loses its identity. Such products as tripe, heart, and scalded stomachs are high in protein, completely edible, wholesome, and nutritious, and most are already used in sausage without objection.” Pork patties could be shaped into any form and marketed in restaurants or for airlines, solving a secondary problem of irregular portion size of cuts such as pork chops. In 1981 McDonald’s introduced a boneless pork sandwich of chunked and formed meat called the McRib, developed in part through check-off funds [micro-donations from pork producers] from the NPPC [National Pork Producers Council]. It was not as popular as the McNugget, introduced in 1983, would be, even though both products were composed of unmarketable parts of the animal (skin and dark meat in the McNugget). The McNugget, however, benefited from positive consumer associations with chicken, even though it had none of the “healthy” attributes people associated with poultry.

In other words, the McRib, or at least the restructured meat products like it, consists of staples—or even specialties—of other cuisines. Take pig heart, for instance. If you’d like to cook it yourself, here’s a 1945 recipe from Gourmet: Coeur de Porc en Civet à la Pompadour, i.e. stewed pig’s heart à la Pompadour, or bopis, a Filipino pig heart recipe. These sorts of things being unappetizing to the American palate, they’re shredded and restructured into an obviously fake rib.

The funny thing about it is that everyone’s in on the joke. It’s clearly not a rib. Until I started reading up on it, I had no idea what was in a McRib. And I’m actually less grossed out by the concept now that I have a sense of what’s in it. Tripe? Ok, that’s cool. But ten years ago the idea of tripe would have made me queasy. I had to go all the way around and come back to accept the McRib.

But all Mandigo—whose son, amusingly enough, is a gourmet butcher—did was provide the technology. The McRib itself was the brainchild of Rene Arend, a native of Luxembourg who first appeared in the Chicago area not as McDonald’s first executive chef, but as a 31-year-old night head second cook at the Drake and a protege of “great chefs in Strasbourg, France.” Arend won a 1959 gourmet contest at the Drake with his supreme de poularde Amphitryon—chicken in sweet butter with cognac Martell, Madere sauce, cream, and goose liver, accompanied by veal dumplings and hearts of palm covered in orange hollandaise sauce—”fixed up for tastes of American people,” Arend told the Tribune. Arend moved to the Whitehall Club before being lured away by the hours, benefits, and challenge of McDonald’s in the late 1970s by Ray Kroc, a Whitehall regular:

Given that Chef Rene is a native of Luxembourg, a graduate (first in his class) of the College Technique Hotelier de Strasbourg, and a man who has prepared dinners for such luminaries as Queen Elizabeth II of England, the king of Belgium, and Sophia Loren and Cary Grant, we asked him why the McFood at McYou-Know-Where’s doesn’t exactly taste like European gourmet cooking.

”We have to cater to the American public,” he replied. ”I am 31 years here, nearly as long as McDonald’s. I have also become Americanized. McDonald’s is perfect American food, you see. But never are any restrictions put on me when I do a product.”

The McRib, patterned after the pulled-pork barbecue Arend ate in South Carolina—pork barbecue itself being a means of dressing up low-cost meat in the impoverished South—was an initial failure, but it’s obviously popular enough maintain a large cult following. And it’s that same cult following that drives the McRib back underground:

And to this day, the McRib comes and goes from the McDonald’s menu for reasons that have to do with its intense popularity and a national supply of pork trimmings that’s typically a lot more limited than the supply of beef trimmings.

“If you suddenly start to buy a large amount of that material,” said Mandigo, “the price starts to rise.”

As the cost to McDonald’s rises, the McRib tends to go out of circulation again. And then the same parts of a hog tend to flow back into the processing lines for Spam, Vienna sausages and other specialized products.

So when the McRib disappears again, you now know what to do: bread crumbs, Spam, and barbecue sauce.