How a soy-root protein reaches a burger
Soy plants make leghemoglobin inside small root nodules, where the plant partners with bacteria that convert nitrogen from the air into a form the plant can use. The molecule helps manage oxygen in those nodules. Its iron-containing heme group is also what gives it a deep red color and helps create the savory, slightly metallic notes associated with meat.
Rather than harvest enough of the protein from soy roots for commercial food production, manufacturers can use yeast as a miniature production system. In fermentation tanks, yeast grows and produces leghemoglobin; the protein is then collected and added to the burger mixture. The yeast is a way to make the ingredient at scale, not what makes the finished patty look as if it is bleeding.
What happens in the pan
Heme is the key to the effect. In a raw patty, leghemoglobin’s red pigment helps give the mixture a meat-like color. As the burger heats, the protein and other ingredients change, and the surface browns. The combination of color and savory aroma makes the cooking process feel familiar to someone used to beef.
The red liquid that can appear in a plant-based patty is not blood. It comes from the burger’s moisture and coloring ingredients. Leghemoglobin supplies a plant-based version of a molecule that helps explain why meat has its distinctive color and flavor, while fermentation makes that ingredient practical to produce without extracting it from vast quantities of roots.
