Here's one for all those vegetarians out there who sometimes just really feel like a good ol' hamburger - a veggie burger complete with what looks like a perfectly cooked, medium rare beef patty.

The burger is the brainchild of biochemistry professor Patrick Brown from Stanford University in the US, and it's now being manufactured by his food company, Impossible Foods. The secret ingredient is called heme, or 'plant blood', which is an organic molecule found in the protein leghemoglobin - the plant version of haemoglobin.

Heme can be extracted from the roots of nitrogen-fixing plants such as peas and beans. Unlike many other types of plants, nitrogen-fixing plants can't source nitrogen from the atmosphere without the help of a common bacterium called Rhizobium. Rhizobium infects legume plants, and together with the leghemoglobin protein, assists them in taking in nitrogen from the air so they can convert it to nitrogen gas, and store it in their roots.

Which is all very efficient and clever, but what's particularly relevant to Brown in this scenario is the fact that each heme molecule with the leghemoglobin protein is arranged in a circle, and in the middle of that circle sits an iron atom. This gives the heme molecules oxygen-attracting qualities - just like the haemoglobin in our blood - and when the heme and oxygen molecules bind together, they change colours, becoming noticeably redder. 

Heme also creates flavours not unlike the ones we taste in meat when it's exposed to sugars and amino acids. So what Brown had to do was come up with the perfect formula for his veggie patties using heme and a variety of different plant-based compounds to not only replicate the flavour of meat, but also the textures of animal fat, muscle fibre, and tissue.

"Livestock is an antiquated technology," he said to Evelyn M. Rusli from The Wall Street Journal. "The system that we use today to produce meat and cheese is completely unsustainable. It has terribly destructive environmental consequences."

Rusli reports that Brown's veggie patty is not quite there yet - its texture is more that of a turkey patty rather than a ground-beef patty - and says that each one costs $20 to make. Which sounds pretty steep, but that's a veritable bargain when you compare it to the ridiculous $325,000 burger being made from lab-grown stem cells by researchers in the Netherlands.

Impossible Foods has just announced that it's secured $75 million in venture capital, including cash from Bill Gates and Google Ventures, so Brown has every opportunity to perfect his veggie burger. "We want the hard-core beef lovers, the guy who's basically saying, 'You know, I'm literally on the opposite pole from a vegetarian, in no conceivable universe would I accept any substitute for meat'," he told The Wall Street Journal.

Sources: The Wall Street Journal, Grubstreet