“How is decaf coffee made?” has quite interesting answers! Simply, decaf coffee is made by isolating and dissolving the caffeine from un-roasted coffee beans.
There are four methods of decaffeination. Two of the methods use solvents to dissolve the caffeine. The third method uses only water, and the fourth uses carbon dioxide. But, we’ll get to this later.
I spent days researching this topic and I really enjoyed it! I hope you find it as interesting as I did.
How is decaf coffee made?
These are the four decaffeination methods in a nutshell. We’ll take a closer look later on in this article. If you’re impatient like me, click the arrow ↓ to jump to those sections.
1. Direct Method ↓
Green coffee beans are steamed, then rinsed in a solvent to remove the caffeine.
2. Indirect method ↓
Green coffee beans are soaked in water, dissolving the caffeine and flavour compounds. The caffeine is removed from the water (not the beans) with a solvent. Then, the beans soak up what’s left in the water.
3. Swiss Water® Process ↓
Green coffee beans are soaked in water, dissolving the caffeine and flavour compounds. The caffeine is filtered out of the water and the water is then used to soak a new batch of green beans. The water removes only the caffeine from the beans.
4. Supercritical Carbon Dioxide (sCO₂) ↓
Green coffee beans are steamed, then mixed with sCO₂. This targets and removes only the caffeine from the green beans. The caffeine is removed from the sCO₂ and reused.
Background on decaffeination
Before diving into the science behind how decaf coffee is made, let’s take a step back and look at what, who and the how of decaffeination.
What is caffeine and decaffeination?
I’m not a scientist, so don’t worry, we’re not going to get crazy with technicalities here. We’ll keep this as simple as possible.
Caffeine is a natural substance found in many plants across the world. It’s a compound in coffees, teas, sodas, etc. that stimulates our central nervous system.
Decaffeination is the process of removing caffeine from a product. For decaf coffee, a caffeine content reduction of at least 97% is required under United States standards.
In the EU, a product is considered decaffeinated when the “caffeine content does not exceed 0,3 % by weight of the coffee-based dry matter.”
Caffeine is a stimulant and also the world’s most widely consumed psychoactive drug.  Although there are plenty of health benefits of consuming caffeine, there are also health risks. It’s for this reason that some might prefer their brew caffeine-free.
This is where decaffeination steps in. At first glance, this may sound simple enough. Just, you know, take the caffeine out…right? Well yes and no.
How do you decaffeinate coffee?
Usually, decaffeination involves soaking coffee beans when they’re still green.
This makes the caffeine inside soluble, meaning that it can be dissolved. Unfortunately, essential coffee oils that make up taste and aroma also get extracted in the process.
Caffeine is soluble. If we put green coffee beans in water for long enough, the caffeine will dissolve into the water. Then we can just throw out the water, dry our beans and enjoy our decaf coffee.
Well, let’s not throw the beans out with the bathwater.
Caffeine isn’t the only soluble substance in coffee. The flavour and aroma compounds and oils in coffee are also soluble. Solubles make up about 30% of a coffee bean’s mass according to this article.
The coffee oils and compounds that make up aroma and taste are referred to as coffee solids.
This means that the water we were about to chuck out also holds a large part of the coffee’s taste. If we throw that out, the coffee is going to taste awful!
This article reminds us that caffeine is one of the components which gives coffee its bitter, acidic flavour. By removing it from the coffee, we’re making the coffee’s flavour milder and less exciting.
The challenge now is to target and remove only the caffeine and leave the coffee solids untouched.
Did you know cold brew usually has a higher caffeine content that other coffee because of the prolonged extraction time? Learn how to make cold brew coffee.
How do you remove only the caffeine from a coffee bean?
The best decaffeination method is supercritical carbon dioxide decaffeination (sCO₂). The next best method is the Swiss Water® Process.
Regardless of the method used, at least some amount of coffee solids will be extracted along with the caffeine. This is because most methods aren’t able to be selective enough.
Other factors make the extraction of coffee solids an unavoidable side-effect of the decaffeination process. One such factor is the impact that the heat of water has on the solubility of the coffee solids.
Out of all the methods, sCO₂ is by far the best at extracting only caffeine. According to this article posted by the University of York, “extraction using sCO₂ is a highly selective process. It only extracts the caffeine compound and leaves the other flavour precursors in the bean.”
Again, I’m not a scientist so I’ll keep this section short and simple.
All four decaffeination methods use solvents to extract and/or dissolve the caffeine.
Solvents are substances that dilute a solute. The solute is the thing that gets dissolved.
In the case of decaffeination, caffeine is the solute (the thing being dissolved). So, what are the solvents?
Before we move on, just a heads-up, I’ll be using the word volatile in this section. No, I’m not talking about anyone’s stepmother.
A volatile substance evaporates easily at normal temperatures.
Is water a solvent? Yep! Water dissolves more substances than any other liquid and is called “the universal solvent.” That’s according to the USGS.
Water is used in some form in all decaffeination methods. Green beans are either steamed or soaked in water.
Ethyl acetate is also called methylene chloride.
It’s a volatile, organic compound according to the national library of medicine. Ethyl acetate is a colourless liquid, and it smells a lot like glue or nail polish. It’s even used as an industrial solvent.
Don’t let that put you off though. Ethyl acetate is actually a natural part of many fruits like apples, pears, oranges, etc.
Marino (2005)  shows that ethyl acetate is produced during the fermentation of fruits and is found in alcoholic drinks, like beer and wine.
That being said, gathering natural ethyl acetate is quite impractical. For the most part, companies use a synthetic form of ethyl acetate.
Or as its friends like to call it, Dichloromethane. Its close friends just call it DCM.
DCM is a volatile, colourless liquid with a chloroform-like odour. DCM is used in many different industries including paint stripping, pharmaceutical manufacturing, paint remover manufacturing, and metal cleaning and degreasing. This is according to the US Occupational Safety and Health Administration.
Supercritical Carbon Dioxide
Supercritical Carbon Dioxide (sCO₂) is pretty cool. We all know carbon dioxide is what we exhale. Carbon dioxide is also called dry ice when it’s cooled down to the right temperature.
Carbon dioxide can be a gas (what we exhale), or a solid (dry ice). The state that carbon dioxide is at depends on the temperature and pressure around it.
If you heat the space around carbon dioxide and increase the pressure enough, it changes to a fluid state. This means that it becomes a liquid and a gas at the same time!
This video explains it quite well.
This state is called ‘supercritical fluid’ and isn’t exclusive to carbon dioxide.
“A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid.” 
I’m not into science or chemistry, but that’s pretty cool, right?
Are solvents safe?
The short answer is, no. You shouldn’t be consuming these solvents for fun. Please don’t do that; it’s not a good idea.
But, the solvents and sCO₂ used in the various decaffeination methods are thoroughly rinsed out of (or removed from) the coffee beans.
The Swiss Water® Process doesn’t even use additional solvents other than water.
To put minds further at ease, the FDA has ruled that minuscule trace amounts of methylene chloride in decaf coffee are not cause for concern. Also, residues of more than 0.001% are prohibited.
The four decaffeination methods
Here are the four decaffeination methods currently being used. The nuances of each method might vary somewhat.
1. Direct Method
- Green coffee beans are steamed for about 30 minutes. This softens the beans and opens up their pores.
- The beans are repeatedly rinsed in a solvent for 10 – 12 hours.
- The solvent, ethyl acetate or methylene chloride, permeates the coffee beans. The caffeine molecules bind to the ethyl acetate molecules. The bonded molecules migrate through the beans’ cell membranes.
- The beans are steamed and rinsed for a few hours to remove as much of the solvent as possible.
- This method decaffeinates the coffee beans by approximately 97%.
The solvent mostly used in this method is ethyl acetate. When this is used, you’ll usually see “naturally decaffeinated” on the packaging. Although, we know now that companies often use a synthetic version of this. So, how natural is it really?
Here’s a video of the process.
2. Indirect Method
- Green coffee beans are soaked in hot water for a few hours. Caffeine and flavour and aroma compounds dissolve into the water.
- The green beans and water are separated.
- A solvent, methylene chloride or ethyl acetate, is added to the water that has the caffeine and coffee oils.
- The caffeine molecules bind to the solvent’s molecules and both are removed from the liquid. This leaves a coffee flavoured water solution.
- The original beans are added to this solution and they reabsorb the flavour and aroma compounds.
- The original flavour of the coffee beans are mostly preserved and are 97% decaffeinated.
3. Swiss Water Process
- Green beans are soaked in hot water, releasing the caffeine and the flavour and aroma compounds.
- The beans are then discarded, leaving a solution of water, caffeine, and coffee solids. This solution is referred to as Green Coffee Extract (GCE)
- The GCE is then run through activated carbon filters to remove only the caffeine. The activated carbon filter has holes large enough to allow water and coffee solids (smaller molecules) to pass through, but not caffeine (relatively larger molecules).
- After filtration, the flavour and aroma compounds (“coffee solids”) remain in the water. The GCE is fully saturated with flavour and aroma compounds but is caffeine-free.
- A new batch of green beans is added to the GCE. The GCE can only extract the beans’ caffeine and not the coffee solids.
- The green beans are 99.9% decaffeinated and dried. The GCE is filtered and reused.
Here’s a video of the process.
The Swiss Water Processing method removes caffeine without using any chemicals, and instead applies the law of simple diffusion. “The movement of molecules from an area of high solute concentration to an area of low solute concentration to ‘even out’ the uneven distribution of molecules.” 
For example, if two coffee beans are soaking in water and one has more caffeine than the other, some of the caffeine molecules will move to the other bean to even things out.
Since the only difference between the mixture and the fresh coffee beans is the caffeine concentration, caffeine molecules will move out of the beans into the mixture of coffee solids, leaving the coffee beans caffeine-free.
4. Supercritical Carbon Dioxide Method
- Green beans are steamed and then placed in a stainless steel drum.
- Supercritical carbon dioxide (sCO₂) is added to the drum.
- sCO₂ behaves like a gas and can permeate substances. The sCO₂ also has liquid properties so it can dissolve substances.
- The sCO₂ penetrates the green beans and binds the caffeine molecules to it. Then it draws the caffeine out of the bean as it leaves.
- The caffeine bonded sCO₂ is then removed from the chamber, leaving decaffeinated green beans behind.
If you missed the bit about sCO₂ above, click this to jump there.
At the time of writing, I wasn’t able to find a video explaining this concept too well. I did find this video that does a good enough job though.
What to do next?
Now you can impress your friends the next time they ask, “How is decaf coffee made?” Read about how much caffeine is in a cup of coffee next.
- Burchfield, G. Meredith, H. (ed.); What’s your poison: caffeine. Australian Broadcasting Corporation. 1997. Archived from the original on 26 July 2009. Available online: https://web.archive.org/web/20090726194701/http://www.abc.net.au/quantum/poison/caffeine/caffeine.htm (accessed on 19th November 2021).
- Marino, D. J.; Ethyl Acetate. Encyclopedia of Toxicology (Second Edition). Elsevier. 2005, 277-279. Available online: https://doi.org/10.1016/B0-12-369400-0/00390-2 (accessed 19th November 2021).
- Schlosky, K.; Supercritical phase transitions at very high pressure. J. Chem. Educ. 1989, 66 (12): 989.
- Anon. Case Study: Removing caffeine from Coffee. 2020. Available at: https://chem.libretexts.org/@go/page/1628 (accessed November 19, 2021).