The Decaffeination of Coffee

Dear Corduroy,

At Caribou Coffee this afternoon I noticed a tag next to their decaf coffee saying “Natural Decaf”. I asked about it and was told they use only water to decaffeinate their coffee. In the past we talked about how other companies use harsh chemicals like methylene chloride to remove the caffeine that hurt the flavor and could be harmful to the drinker. According to Caribou’s website their process preserves “nearly 100%” of the coffee’s flavor. Have you heard about this? Maybe it is time for a taste test.

–Sleepy in Pittsburgh


Maybe you should switch to full-caff and it’ll help you wake up!

I have heard about the water-only decaffeination process (branded as the Swiss Water Process). Its proponents tout it as a way to remove the caffeine without removing the flavor; their case is summed up in a tutorial on the Swiss Water website. The basic process consists of soaking a batch of green (unroasted) beans in hot water, thereby dissolving the caffeine and the flavonoids (compounds responsible for the coffee flavor) out of the beans, discarding that batch of beans, and then using that same batch of water to soak more batches of beans. The caffeine is filtered from the water by means of a charcoal filter; the flavonoids stay in the water.

Because the subsequent batches of beans are soaked in flavonoid-saturated water, they retain coffee flavor while losing caffeine. The process works well (removing almost all of the caffeine and retaining the coffee’s unique flavor) so long as all batches of beans soaked in the water are the same type of bean. Because the flavor components are water soluble, and because the water can only absorb a certain concentration of these flavonoids, it’s easy to guarantee that the beans will leave the process with almost as much flavor as when they entered it, but not that the beans will taste the same. If a batch of Sumantra Mandheling beans is soaked in water that has been used for Kenya AA, Colombia Supremo, and Guatemala Antigua, the beans leave the process tasting like a blend of all four types of coffee because the flavonoids intermingle during the decaffeination process.  In general, though, you should be wary of the “Naturally Decaffeinated” label.  It can be misleading.

Some processors use this label for coffee that has been decaffeinated with the assistance of ethyl acetate, which, though moderately toxic is present in minute quantities in fruit. The other solvent commonly used nowadays to decaffeinate coffee is methylene chloride. Both of these solvents are far less toxic than the solvents that were used when coffee was first decaffeinated: benzene, chloroform, trichloroethylene, and dichloromethane.

When coffee is decaffeinated via the use of solvents, the solvents take the place of the charcoal filters in the Swiss Water process: the solvents never actually come into contact with the beans, but rather strip the caffeine from the water.

The most interesting process of caffeine removal involves the use of pressurized carbon dioxide and is explained very well by Maryland’s Frostburg State University:

using carbon dioxide to decaffeinate coffee
When a sealed vial containing both gaseous and liquid carbon dioxide under high pressure is heated, the liquid density drops while the gas density rises. If the pressure is above 72.8 atm, and the temperature rises above 304.2 K, the density of the liquid and the density of the gas become identical. The meniscus between the liquid and gas phases vanishes. The carbon dioxide becomes a supercritical fluid which has both gaslike and liquidlike properties. The fluid fills the container like a gas, but can dissolve substances like a liquid. Supercritical fluid carbon dioxide is an excellent nonpolar solvent for many organic compounds, including caffeine.

The extraction process is simple. Supercritical carbon dioxide is forced through green coffee beans. Its gaslike behavior allows it to penetrate deep into the beans, and it dissolves 97-99% of the caffeine present.

Coffee manufacturers recover the caffeine and resell it for use in soft drinks and medicines. The caffeine-laden CO2 is sprayed with high pressure water and caffeine is then isolated by a variety of methods, including charcoal adsorption, distillation, recrystallization, or reverse osmosis.

Accepting a decaffeinated coffee inherently means accepting a coffee that has an altered taste because no decaffeination process preserves the bean’s exact state minus the caffeine. There is always some loss of flavor that is easily noticeable when sampling a regular coffee with its decaffeinated counterpart. Perhaps the best metaphor to explain the flavor loss comes courtesy of

One might compare a naturally mellow (low acidity) cup of caffeinated coffee with a decaffeinated version of a high acidity coffee. If you prefer a coffee that is known for bitterness or acidity in the caffeinated version, the same coffee in a decaffeinated state will taste “flat” in comparison. At the same time, the other characteristics of that coffee will be brighter since they aren’t masked by so much bitterness or acidity. It is kind of like an Elvis Presley song. Often times there are brilliant bass lines that aren’t noticed until the vocal track has been removed. In these moments, the full complexity of the song is realized. On the flip side, removing the vocals could reveal an uninteresting tune that is better in a complete state.

One Response to “The Decaffeination of Coffee”

  1. luke Says:

    excellent post. to be frank i am not sure i understood it completely. but, wanted to stop inand leave a note anyway. are you a writer by trade?, because your posts are really strong.

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