How is Coffee Decaffeinated?
I often get asked by my coffee roasting community why roasting decaf beans is such a tricky business. What’s with the dark brown color of green decaffeinated beans? Let me explain.
Firstly, coffee is always decaffeinated in its green, unroasted state. Those of us who roast coffee know the challenges of roasting decaffeinated beans because the chemistry of the bean has been disrupted. We’ve opened up the pores for the caffeine to get out. And it’s not just the caffeine that escapes. Around a 1000 flavor compounds also get drawn out of the bean and these have to be put back in again. That’s why a good cup of decaf is so hard to find.
Coffee principle: The bean is never the same afterwards. And when roasting decaf coffee beans, there’s so little time between first crack and over-roasting. Small margins. A fine art.
So How Do We Decaf Green Beans?
Since caffeine is water soluble and bonds with the water molecules, all decaffeination processes use H2O. But water isn’t selective, it removes other soluble substance like sugars and proteins. To speed up the process and minimize the washed-out taste of decaf, other agents are brought in.
These agents come in two types:
Two types of solvents are used:
- methylene chloride
- ethyl acetate
If you see the words “naturally decaffeinated” on a coffee label it means ethyl acetate has been used, because it’s found in minute quantities in ripening fruit such as apples and blackberries. That’s not the whole story though because naturally occurring ethyl acetate would be too expensive so instead a synthetic product is used – most commonly from petroleum derivatives.
That’s the basics covered. Now, there are two methods for how the solvent works – either directly or non-directly.
Doing it the non-direct way means the solvent never touches the beans. This way starts by soaking the beans in hot water for two hours and then pumping the caffeine-laden water into another tank. At that point the solvent is added. It bonds to the caffeine molecules. That’s evaporated off and the flavour compounds and coffee oils in the water are put back in with the beans to be soaked up.
The direct way involves steaming the coffee beans for up to two hours to open the pores then bathing the beans for about ten hours in solvent. The caffeine-laden solvent is then drained away and the beans are steamed again to remove any residue.
Is the solvent compound bad for you when used in this direct way? Highly unlikely because the chemical evaporates at 104 degrees. Gone! Any traces are eliminated when the beans are roasted at 400 degrees. Even after, you brew the coffee at 200 degrees.
Everything about decaffeination seems to come in twos, like animals in an ark.
The two non-solvent methods are:
- CO2 process
- Swiss Water Process
Swiss Water Process
The Swiss Water Process uses solely water and osmosis. It starts the same way as the direct solvent method. The coffee beans are soaked in hot water for two hours. What happens next is different. The water is run through an activated charcoal filter to filter out caffeine. The beans are discarded and the flavor infused water goes into another tank, where it’s used to draw the caffeine out of a fresh batch of coffee beans. Magic. The beans stay infused with the flavour. They filter it back through the charcoal and keep the process going. That’s also where you get green coffee extract.
In the CO2 method the beans are soaked in hot water in a stainless steel tank, which is then sealed. Then, liquid CO2 is pumped in under 1,000 psi of pressure. That pressurized CO2sucks the caffeine out of the beans. The pressure is let off and CO2 bonded to caffeine goes back to its gaseous state, depositing the caffeine. The caffeine-free CO2 is pumped back into the pressurized tank.
Because it’s expensive, this process is used in high-volume, commercial grade decaf.
Wouldn’t it be much easier to grow coffee beans that don’t contain caffeine in the first place? Well, progress is being made with a bean called Decaffito, already trademarked in Brazil. [https://en.wikipedia.org/wiki/Decaffeination]
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