The cook, complete with hair net, lays the red patty down on the grill and gives it a press with a spatula. And there, that unmistakable sizzle and smell. She flips the patty and gives it another press, lets it sit, presses it, and pulls it off the grill and onto a bun.

This is no diner, and this is no ordinary cook. She's wearing not an apron, but a lab coat and safety goggles, standing in a lab-kitchen hybrid in a Silicon Valley office park. Here a company called Impossible Foods has over the last six years done something not quite impossible, but definitely unlikely: Engineering a plant-based burger that smells, tastes, looks, and even feels like ground beef.

There are other veggie burgers on the market, of course, but Impossible Foods wants to sell consumers a real meat analog—one that requires a very different kind of engineering than your Boca or black bean burgers. So WIRED wants to take you on the deepest dive yet into the science behind the Impossible Burger.

Biting into an Impossible Burger is to bite into a future in which humanity has to somehow feed an exploding population and not further imperil the planet with ever more livestock. Because livestock, and cows in particular, go through unfathomable amounts of food and water (up to 11,000 gallons a year per cow) and take up vast stretches of land. And their gastrointestinal methane emissions aren’t doing the fight against global warming any favors either (cattle gas makes up 10 percent of greenhouse gas emissions worldwide).

This is the inside story of the engineering of the Impossible Burger, the fake meat on a mission to change the world with one part soy plant, one part genetically engineered yeast—and one part activism. As it happens, though, you can’t raise hell in the food supply without first raising a few eyebrows.

The Lean, Mean Heme Machine

What makes a burger a burger? The smell, for one, and taste and texture, all working in concert to create something animal. It’s loaded with all manner of proteins that interact with each other in unique ways, creating a puzzle of sorts. But Impossible Foods thinks the essence of a meat lies in a compound called heme, which gives ground beef its color and vaguely metallic taste—thanks to iron in the heme molecule. In blood, heme lives in a protein called hemoglobin; in muscle, it's in myoglobin.

Interestingly, you’ll find globins (a class of proteins) not just across the animal kingdom, but in plants as well. Soy roots, for example, carry a version called leghemoglobin, which also carries heme. Leghemoglobin in soy and myoglobin in meat share a similar 3-D structure consisting of what's known as an alpha helical globin fold, which wraps around the heme.

So what if you could extract the heme from a plant to obtain that secret ingredient in ground beef? Well, the main problem, Impossible Foods found, is that you'd need a heck of a lot of soy: One acre of soybeans would yield just a kilogram of soy leghemoglobin.

Impossible Foods founder and CEO Pat Brown figured out how to hack together a better way. Technicians take genes that code for the soy leghemoglobin protein and insert them into a species of yeast called Pichia pastoris. They then feed the modified yeast sugar and minerals, prompting it to grow and replicate and manufacture heme with a fraction of the footprint of field-grown soy. With this process, Impossible Foods claims it produces a fake burger that uses a 20th of the land required for feeding and raising livestock and uses a quarter of the water, while producing an eighth of the greenhouse gases (based on a metric called a life cycle assessment).