Thu. Jan 23rd, 2020

How to decaffeinate a coffee?

1819. It all started with the courtesy gift of a poet.

Friedlieb Ferdinand Runge was a Hungarian chemist dedicated to the extraction of Belladonna compounds, a medicinal plant known to have a relaxing effect in small amounts, but lethal in high doses. In his studies he managed to isolate atropine, a molecule that enlarged the pupils of the one who consumed it and that allowed the treatment of some eye diseases. This caught the attention of the poet and scientist Johan Wolfrang von Goethe, who invited Runge to his house for dinner and to talk about his work.

Far from bringing some graphics with results, Runge wanted to prepare a surprise and took a cat from his laboratory. In front of Goethe, he supplied the cat with a controlled dose of atropine, and they spent the next few hours gazing at the cat with huge pupils in front of them. Goethe was so surprised that he decided to give Runge a gift for the inconvenience. A friend had brought him from Greece a rare product to find in Hamburg: a package of coffee beans. When accompanying him to the door, Goethe gave him the package saying: “Hopefully, you can get something interesting out of here.” Several months later, Runge became the first scientist to discover and isolate caffeine.

Despite his discovery, Runge was more interested in continuing to investigate belladonna, so, coffee, he only dedicated a study describing the method of extraction from grains. Later, in 1827, scientist Michael Oudry isolated another molecule with similar properties from the tea leaves he called theine. It wasn’t until eleven years later that, after analyzing both molecules, the scientists showed that they were exactly the same. That confusion still has consequences today, since although caffeine is the official name, it is also called teina or guaranina depending on its origin. In fact, tea leaves have a higher concentration of caffeine than coffee beans, but the amount of tea we need for a cup is less, so tea is considered as low in caffeine.

The stimulating effect of caffeine makes it a popular product. Currently 85% of Americans consume a drink with caffeine a day through coffee, tea or soft drinks. But despite being safe in normal doses, some people are especially sensitive to its effects and may feel insomnia, anxiety and a mild addiction to this molecule if they consume it regularly.

This caused that, along with the increase in the popularity of coffee, a parallel desire arose: to create decaf coffee. A coffee that would not give us problems and we could drink without thinking about its side effects. But at the chemical level, decaffeinating coffee is a challenge for a simple fact: then we must drink that coffee.

Mugging coffee bean

When Runge extracted the caffeine, it subjected the coffee beans to different chemical solvents to dilute and separate their components. Although it allows the separation of caffeine, this process degrades the rest of the coffee bean, affecting all the chemical components that give it smell and taste. In addition, the solvents that are used for the extraction are not suitable for human consumption, so with the Runge method we will only obtain a discolored, tasteless, probably toxic coffee, although without caffeine.

There are more than four hundred different chemical compounds in a coffee bean, in a very specific proportion according to the grain species. The challenge of decaffeination is to release the caffeine from the grain but make the rest remain within the grain in concentrations similar to those they had. Currently there is no perfect method to remove only caffeine, always take a part of the rest of the grain. This affects the taste, causing us to notice a different taste in decaffeinated coffee.

But there are some more effective methods than others. The first method was discovered by chance by the German merchant Ludwig Roselius, in 1906, when washing coffee beans with salt water he noticed that caffeine was lost, leaving a lighter taste. Based on several tests, he created the first method of decaffeination baptized with his last name.

The Roselius process is simple: first the coffee beans are washed with salt water, causing them to break and allowing them to exchange chemical compounds with the outside. Up to twelve washes are then carried out with benzene, a chemical compound capable of dissolving substances that are insoluble in water. With each wash, the compounds that best dissolve in the water remain in the grain and those that do the worst are dissolved in the benzene, taking most of the caffeine.

As the coffee flavor is given by compounds that dissolve in water (and precisely because of this we make an infusion with hot water) the flavor remains more or less stable, and the caffeine decreases a lot even if it does not disappear. This decaffeinated coffee was a bestseller and was marketed last century in Europe under the Koffee-HAG brand. The problem is that it was discovered that the benzene with which the washes were performed is carcinogenic and the process is no longer performed today. In substitution, other solvents with the same properties, but suitable for human consumption, such as methylene chloride, are now used. Even with another solvent, a drawback of this method is that part of the solvent remains in the coffee bean, affecting its flavor. To avoid this, we have the second system: bathe coffee beans in … decaffeinated coffee.

Osmosis is a phenomenon whereby chemical substances dissolved in two liquids brought into contact can be exchanged with each other to equalize. Thanks to osmosis, if coffee beans are bathed in coffee, nothing will happen to them because the inside and outside of the coffee bean contain the same compounds in the same concentration. But if the coffee outside is decaffeinated, the caffeine inside the grain will go outside to balance. With this method we remove only the caffeine from the coffee beans with the advantage of not adding any foreign solvent, since there is only coffee. The “recaffeinated” coffee is filtered separately to remove the caffeine through other processes that break the coffee but as it will not be taken at any time they can afford.

This method is better but we can go to the latest technology, to the most modern system that produces the best tasting coffees, but also the most economically expensive: using liquid carbon dioxide. In this method, coffee beans and carbon dioxide (which is the gas that emits our breath) are subjected to tremendously high pressures, up to 300 atmospheres

Carbon dioxide has a peculiarity, and it is that at the correct pressure it is able to diffuse as a liquid and penetrate into coffee beans, dissolving non-water soluble molecules such as caffeine. When the pressure drops, it becomes a gas again and escapes the coffee bean, leaving no residue. This treatment is the best we have at the moment, but it is also the most expensive to perform, since it is difficult to maintain the pressure of the container. This makes decaffeinated coffees with this technique have a higher than average price.

Whether through solutions, gases or other coffee samples, we have learned to penetrate the impregnable border of coffee beans to get decaffeinated coffee. Something that would not have been possible without knowing the caffeine thanks to a farewell gift. Not bad, Goethe.


  • Although some studies show that drinking a cup of coffee has a diuretic effect, drinking coffee regularly generates resistance that causes this effect to disappear.
  • The body absorbs caffeine very quickly but gets rid of it at the same rate. After ten hours, 75% of what is ingested disappears, so breakfast coffee does not affect the night’s sleep.
  • Theine and caffeine are exactly the same molecule.



Source link