Here's the ingredient that makes Impossible burgers possible

When you bite into a meatless burger, you may notice that it “bleeds.”

That’s a feature companies like Impossible Foods have been working on for years. The distinct red color is part of the patty’s appeal, allowing it to look and taste like real meat.

In a report with the Associated Press,  biochemist Smita Shankar explained that the key ingredient used to give burgers that bleeding effect is actually engineered rather than extracted from a plant.

To replicate the taste of meat, the company scanned plants for molecules that mimic a protein in meat that contains iron, which makes blood red. They finally settled on soy leghemoglobin, which is found in the root of soy plants.

The company website touts its plant-based foods, but “no plant is actually touched” in the process of making its infamous "burger." Instead of using those plants directly, they insert synthetic versions of sections of soy DNA into yeast so it produces soy leghemoglobin during fermentation.

The ingredient is meant to be less than 1% of the patty.

Many ingredients don’t need approval from the Food and Drug Administration. Companies often hire scientific experts to declare ingredients to be “generally recognized as safe.” Impossible Foods says soy leghemoglobin met that requirement in 2014.

Still, critics like the Center for Science in the Public Interest and Environmental Defense Fund have taken issue with companies make their own consumption safety determinations.

A lawsuit by advocacy groups against that system is ongoing.

Impossible Foods isn’t just using soy leghemoglobin for patties. The company recently announced using it in a fishless fish recipe.