SuperMeat, an Israeli start-up, is running a splashy crowdfunding campaign to create lab-grown chicken, making all the usual lofty promises about lab-grown meat: It’ll stop animal suffering! Save the planet! End hunger! But in a new twist, it’s also touting the endorsement of an unexpected group: rabbis, who say its chicken will be kosher.

If only it were that simple. As the joke goes: two Jews, three opinions. SuperMeat co-founder Koby Barak acknowledges that more conservative rabbis have different interpretations on what makes lab-grown meat kosher. And because SuperMeat hasn’t actually grown any chicken yet—it’s raising money to fund a proof of concept—“too many variables are unknown” to go into details about how SuperMeat will get kosher certification, he says.

But why let that stop us from overthinking the question of whether lab-grown meat is kosher? Asking the question is also a way of asking how lab-grown meat is actually made. Just as a box of corn flakes may contain corn from a farm in Iowa, calcium mined from limestone, and vitamins chemically synthesized from petroleum, lab-grown meat is the sum of its components: blood serum from unborn cows, collagen from animal hides—or, as with SuperMeat and other researchers aiming for cruelty-free lab-grown meat, none of the above.

“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.

The pork was a bridge too far. Once people found out about the pork skins, many rabbis had to retract their endorsements of the jiggly dessert. The whole episode underscored how industrialization was changing food. “They didn’t realize the door they opened by allowing these transformed products,” says Horowitz. “That’s why the dominant kosher certifiers closed the door when they realized they were on a slippery slope.”

Post, at Maastricht, originally used animal-based collagen to grow beef, but he’s now experimenting with polymers from plants, seaweed, and mushroom. Others have tried edible protein in tofu and Quorn, the meat substitute derived from a fungus. But while muscle cells naturally take to collagen—just as they do in an animal’s body—they don’t quite fit right with plant-based proteins. It’s possible, says Post, but “it needs a couple of tricks.”

3. Lab-grown meat uses fetal cow blood

Keeping animal cells alive in a dish is tricky, and the magic ingredient has long been fetal bovine serum, which is derived from the blood of unborn calves. It’s rich in the proteins and nutrients that animal cells need. It’s also a byproduct of industrial farming, as the serum comes from fetuses found inside cows being slaughtered.

This is a problem because lab-grown meat can’t rely on byproducts of industrial farming if it is going to replace industrial farming—and the serum is unlikely to be kosher. That’s because the cows mostly likely to be pregnant with a fetus at the time of slaughter, says Cornell food science professor Joe Regenstein, are dairy cows being culled due to age or disease. And cows that are too sick at the time of slaughter will not pass kosher inspection.

The good news, though, is that companies supplying biology labs do make animal-free serum substitutes. The bad news is that nobody knows exactly what is inside those alternatives, not even the researchers who use them. (It’s probably some combination of stuff derived from plants, bacteria, or yeast.) “It’s actually proprietary,” says Post, who uses these animal-free alternatives in his lab. “The commercial sources don’t reveal it, and it’s a little bit annoying that we’re working with a blackbox.” In Post’s experience, the animal-free substitutes do work, though cells grow a little differently than they do with fetal bovine serum.

The mystery of that’s inside the serum substitutes may be annoying for researchers, but it will be a real problem for food regulators. A typical serum substitute might contain over a dozen ingredients, and under kosher law, someone would have to trace each and every ingredient to make sure it was made in a kosher facility. It’s just like if you wanted to sell pizza as kosher: the flour, yeast, tomato sauce, and cheese all need to be kosher certified.  “I don’t think it’s trivial to have a kosher cell culture,” says Regenstein.

And even if you don’t keep kosher, all of this stuff is going to affect you. Consider that only 2 percent of Americans are Jewish, yet 41 percent of packaged goods sold in the U.S. are kosher. It’s partly because of kosher’s halo effect—people rightly or wrongly perceive kosher as higher quality—and it’s good business sense for manufacturers. A big flour manufacturer might not want to keep separate facilities for its kosher and non-kosher flour, so it just makes everything kosher out of convenience. And big food buyers like Sysco, which distribute to restaurants, hospitals, and schools, prefer the ease too. Kosher rules end up having an outsized impact on our food system.

As the technology for lab-grown meat inches forward—and make no mistake, it’s still far from ready for grocery shelves—kosher and non-kosher eaters alike might have the same question: Where do all parts of this meat come from? Scientists are still working that out. And the concerns of Jewish dietary law could very well shape where the ingredients of lab-grown meat come from.