As we learned from a previous post, supercritical fluid is (sort of) another state of matter. It’s one that’s not a gas, not a liquid, but with properties of both.
While the phenomenon was discovered over two hundred years ago by Baron de la Tour of France (more on that in a minute), its use really gained popularity in the 1970s. Long before you could pop a pod into the sleek machine on your countertop and push a button, there was Sanka and Nescafe – decaffeinated instant coffees. (I remember my grandmother drinking Sanka in the ‘70s.)
Solvents like trichlorethylene in methylene chloride were used in the decaffeination process – the same solvents used in dry cleaning and paint remover! Those solvents left a residue in the coffee.
Government health officials around the world started to require that companies reduce the solvent residue in the coffee. But how? Getting levels low enough to comply with standards was difficult and expensive. They needed an alternative.
Let’s go back to Baron de la Tour. During one of his experiments, he took a cannon, put a cannonball in it, partially filled it with a liquid, and then sealed it up. He then applied heat and rocked the heated cannon back and forth. Initially he heard the characteristic sloshing of the liquid and the impeded movement of the cannon ball. Since this was a closed system of 2 phases, liquid and gas, he thought this would continue endlessly. However, as the heating continued, he no longer heard the liquid sloshing, and the cannon ball rolled back and forth effortlessly. As the temperature and pressure increased, seemingly the 2 phases, liquid and gas, melded into one single phase which we now call supercritical fluid.
Fast forward to the 20th century. In 1967, Kurt Zosel of the Max Planck Institute for Coal research was studying separation methods. He experimented with decaffeinating coffee and found that supercritical CO2 was able to isolate and extract the caffeine from coffee beans while leaving the other compounds untouched.*
Zosel’s discovery led us to one of the methods of decaffeinating the coffee we drink today.
*For more information on the process, visit Mission Coffee Works.