“Modern kosher law forces you to trace the product down the chain, in a way that contemporary food regulation does not,” says Roger Horowitz, a historian and author of Kosher USA: How Coke Became Kosher and Other Tales of Modern Food. To deem lab-grown meat kosher, a certification agency would have to track down the origin of the muscle cells, the ingredients that nourished those cells, and the material they’re grown in—and each of these steps happens to intersect with big technical hurdles for growing meat in a lab.

1. The origin of meat

Lab-grown meat all starts with a small number of cells taken directly from an animal’s muscle. To create the first $325,000 lab-grown hamburger in 2013, Mark Post at Maastricht University made regular trips to a slaughterhouse to take samples from freshly killed cows.

Jewish dietary law, when it comes to meat, covers both what is forbidden (pork, shellfish, etc.) and how non-forbidden animals like chicken and cows should be slaughtered. So that gets to the first dilemma: If cells are taken from a live animal via biopsy, can the hamburger or chicken nugget grown from those cells be kosher? Or do the cells have to come from a kosher slaughtered animal?

Rabbis in SuperMeat’s video explain that the origin of those cells does not matter due to the concept of panim chadashot, literally “a new face,” because the end product is so transformed. Applying panim chadashot could also make sense if scientists can, as they eventually hope, establish self-replicating lines of chicken cells that live on in a lab decades after the original chicken died. Stricter rabbis though, says Horowitz, will probably require the cells to be of kosher origin, too. (So no kosher lab-grown pork in this case.) But individual judgments on this matter are up to kosher certification agencies like the Orthodox Union and OK Kosher.

2. Lab-grown meat uses collagen from animal bones and skin

A steak is much harder to culture in a lab than a hamburger. “The cultured hamburger was a mass of myotubes,” aka muscle fibers, says Erin Kim of New Harvest, a nonprofit that funds research into lab-grown meat. The key to growing steak with the right chew is scaffolding, basically a gel that muscle fibers can attach onto.

And what’s great for making scaffolding? Collagen, a protein found in animal muscles, bones, and skin. Collagen also happens to be the source of a great kosher controversy that engulfed Jell-O in the post-war era. Rabbis had originally okay’d Jell-O, which used gelatin extracted from collagen in non-kosher cow bones, because of panim chadashot. (Powdered gelatin of course looks nothing like animal bone.) But after World War II, the gelatin industry quietly began switching out cow bones for an easier source of gelatin: pork skins. In his book Kosher USA, Horowitz describes how pork skins were frozen into hundred-pound molds and shipped by railroad to a gelatin plant.