These are derived from plant carbohydrates that human enzymes are unable to break down.

ECONOMIST: Modern medicine

At Virginia Tech, Zhang has been researching ways to use enzymes to extract hydrogen from plant biomass.

FORBES: Could Hydrogen Breakthrough Revive The Fuel-Cell Car?

But that might alter when biotechnology delivers new enzymes that can make ethanol efficiently from just about any sort of plant material.

ECONOMIST: The future of energy