By now you may have seen the bizarre photo of pink goo - more milkshake than meat - which in reality was a pre-production hamburger patty, treated with ammonium hydroxide, a chemical found in household cleaners and fertilizer. It's also used to kill bacteria. It was also used in burgers from fast food giants like McDonald's and Burger King.

Meat treated with ammonium hydroxide. by Alex Parker

But no more.

British tabloid The Daily Mail reports that McDonald's ended the practice in the summer. The paper credited celebrity chef Jamie Oliver's campaign against meat treated with ammonium hydroxide as a catalyst for the decision, but McDonald's denied that. The Daily Mail reported that Taco Bell and Burger King have also ended the practice.

Oliver shocked audiences when he showed how meat - the cuts often left to make dog food - made its way into restaurants, school lunches and home kitchens.

I also came across some information about the bizarre, but oh-so-tasty, delicacy is the McRib, the limited-time-only meat patty that is literally shaped in a pan to look like pork ribs.

Chicago Magazine explains the evolution of the McRib, invented by Meat Industry Hall of Famer Roger Mandigo, and why it is so darn limited.

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.

As for why it comes and goes, it's not due to a marketing campaign. It's not even a case of demand. It's all supply, according to the Lincoln, Neb. Journal-Star:

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.