Up for more technical discussion of the chemical composition of tea? Of course you are! You aren’t going to find out how they get the caffeine out of tea leaves without vocabulary that I, at least, thought I had escaped when I fled my high school chemistry class. The story has a happy ending, though, at least for people who get their decaf tea from our tea shop, so you can read on with the same confidence that you go to a mainstream scary movie with, the pretty heroine will make it out alive, and without even drinking something called dichloromethane.

How Tea is Decaffeinated

Here’s the basic outline for how things are decaffeinated: first, the leaves are soaked in a little water if it’s been dried, so that the chemicals can move around properly. The point of drying them out in the first place is to stop chemical reactions from happening until you combine them with hot water to get them to react into a nice cup of tea, so this has to be undone first. Second, the leaves are exposed to a solvent that dissolves out the caffeine, hopefully leaving the rest of the chemicals in the leaves mostly alone. Then they re-dry the leaves, and voila! The decaf version.

Wait, solvents? Do I want to drink those?

That second step is dodgy, though. First, there is a selection of solvents. Once the solvent touches the leaves it never all comes off, so this is important to you, the decaf drinker, because you’re drinking your solvent, too. One, the dichloromethane from the first paragraph, also called methylene chloride, is such an effective solvent that it’s also used in paint stripper, degreaser, and dry cleaning solution. As you can imagine, it isn’t the safest thing ever ingested, and the US isn’t wild about letting producers put it in our tea. It’s still used in some countries, though, so there is a chance it could end up on your cheap decaf.

A second solvent, ethyl acetate, is found naturally in tea leaves, and so is often called “natural decaffeination.” There’s a lot more ethyl acetate left on a decaf tea leaf than there would naturally be, and it is derived artificially so they can have enough of it to be useful in industrial processes, so it isn’t really that natural. The third solvent is carbon dioxide, put under enough pressure that it’s almost a liquid. While carbon dioxide is bad for the atmosphere, it’s fine for people, so it’s the solvent you want.

Is the tea still healthy like all the articles say it is?

The other problem with the solvent step is that it’s hard to take out just the caffeine and not anything else. Ethylene acetate takes out a lot of the flavonoids, those anti-cancer chemicals, at least a third and usually more like 70%. There are some processes that can be used to filter the caffeine out of the stuff the solvent takes out and then the producers can try to get the rest of the chemicals to dry back onto the tea leaves, but they don’t work that well for tea. Luckily, carbon dioxide is much better about leaving the other chemicals alone, stripping away only about 5% of the flavonoids.

Here’s how that works: Caffeine molecules are smaller than most of the other molecules that make up a tea leaf, so they’re easier for a solvent to move, and since the carbon dioxide is a gas under a carefully calculated amount of pressure rather than a liquid, it can be calibrated to be just dense enough to be able to carry off the caffeine and not enough to take the bigger molecules. Decaffeination with carbon dioxide is technically called “supercritical fluid extraction,” because the carbon dioxide under pressure is called a supercritical fluid, ie a gas put under so much pressure it passes a critical point and starts to behave kind of like a liquid, doing things like dissolving caffeine. Does anyone else want to burst into “She Blinded Me with Science“?

That was a lot of words, and most of them were really long. What should I actually drink?

So carbon dioxide is definitely your best bet, right? Not poisonous, doesn’t take out all the really healthy chemicals, involves awesome and unlikely states of matter. But how can you tell? No one would put any of these words on packaging. There’s a code, though: in the US, and probably most other countries with strict health laws, you shouldn’t run into methylene chloride. As I said above, naturally decaffeinated usually means they used ethyl acetate, and since it’s cheap, it’s generally the default approach. And finally, if your tea is organic, the only way it can be decaffeinated is with carbon dioxide. So! For maximum healthyness of decaf tea, buy it organic. Makes sense anyway, right? All the decaf tea at Teahouse Kuan Yin is certified organic, and we never even thought about it until this afternoon. I love happy endings!

Elizabeth, Teahouse Kuan Yin Staff