Editor’s Note: This article first ran in the May/June 2020 Issue of Roast Magazine and is republished here with permission. They have graciously provided access to the original in PDF form, downloadable here.
Heading into one of my first coffee industry events, I remember a very well-known coffee professional sighing next to me, with real emotion. When I inquired as to what was the matter, he responded, “Coffee without caffeine would be perfect – then I could drink as much as I want”. Over a decade later, I completely understand the predicament. Coffee has so much to offer but it also has a biological boundary that when crossed, turns that enjoyment into headaches, nausea and worse. Being caffeinated is wonderous, being over-caffeinated hurts, as we all well know.
Although we commonly associate the chemical compound caffeine with the Coffea genus of flowering plants in the Rubiaceae family, it is present in over 60 species of plants, including tea, kola nuts, and cacao. And while we would like to assume that its presence is some cosmically serendipitous happenstance – a stimulating elixir of the goddess, perhaps – it is, rather, a naturally occurring insect repellant.
The Coffea genus has over 100 species, and of the two most commercially available, Canephora (more commonly referred to as Robusta) produces almost twice the amount of caffeine than Arabica, its more favored sister. Both species have been prized for centuries for their stimulating properties, and the discovery of this almost magical effect on the central nervous system is now a legend featuring a goatherd, his goats, and their fabled dancing.
The coffee plant had been anecdotally identified as a stimulant for centuries. However in 1820, under the direction of the poet and statesman Goethe, no less, Friedlieb Ferdinand Runge was tasked with performing the first recorded scientific study of the bean itself. Goethe was an avid student of geology and botany for many years and had been impressed by Runge’s previous work on the belladonna extract. Runge managed to isolate the caffeine compound in its purest form. However, he did not investigate or look even further into what caffeine was or even consider producing a decaffeinated version of this storied bean.
If we are going to spend time looking at the process of decaffeination, we look to understand caffeine itself. Caffeine is an alkaloid, a class of naturally occurring nitrogenous organic compounds of low molecular weight found in around 15% of bacteria and algae, as well as plants and animals. In plants, they are mainly produced as part of their biological system’s above-ground defense mechanism. Other alkaloids, such as strychnine, morphine, cocaine, and nicotine, amongst others, have profound, and well-documented effects on the human body, some of them considered positive at one end of the spectrum, all harmful at the other.
Isolated, in its purest form, caffeine is an incredibly bitter, white, water-soluble compound which is toxic to the point of lethality in high doses, that dose being approximately 150 milligrams per kilogram of body weight. For perspective, the average person drinks about 200 milligrams total in their daily coffee intake. However, it is not recommended you consume more than 500 – 600 milligrams a day, according to medical advice.
While Runge had no interest in producing a decaffeinated beverage for the wider public, his work was instrumental in guiding one who did, Ludwig Roselius, whose accidental soaking of green beans in seawater paved the way for a patented process involving steaming green coffee to remove caffeine, using benzene as a solvent. And thus, around 1914, Sanka (by way of Kaffee HAG), was born.
Fast-forward to today; we now know that benzene is a carcinogen, as well as being highly flammable, and is no longer used as a chemical solvent. However, this process of decaffeinating coffee using a solvent was tried and true and is still the preferred method today, using the relatively safe ethyl acetate and dichloromethane (otherwise known as Methylene Chloride or the acronym DCM) in place of benzene.
It should be noted that although both of these chemicals are considered safe for consumers of decaffeinated coffee, dichloromethane is now thought to contribute to the deterioration of the earth’s ozone layer – a critical component in regulating the earth’s temperature – thereby contributing to climate change. In addition to this, DCM is now banned for sale for use as a paint remover. While dichloromethane is found in nature, for example in oceanic sources, wetlands, macroalgae, and volcanoes, its primary source is industrial emissions. Neither last nor least, when talking about dichloromethane in more general terms, it should be noted that the production of this chemical creates two highly toxic chemicals that are banned for consumer application, carbon tetrachloride and chloroform, both carcinogenic, as well as the former causing liver toxicity. Although dichloromethane is itself a suspected carcinogen and causes severe risk should you inhale or come into direct contact with it, it can be safely used in the process of decaffeination, as the high volatility that makes it so desirable a chemical solvent, also means that it evaporates extremely quickly and leaves little to no residue behind.
Ethyl acetate is a distillate of acetic acid and ethyl alcohol and considered far less of a risk to human physiology than DCM, but it is an irritant and with repeated or prolonged exposure, can cause serious damage to internal organs. Both dichloromethane and ethyl acetate are used in the organic solvent method of decaffeinating coffee. There are two ways to achieve this result, direct contact and indirect contact, and are two of the four different ways that coffee is usually industrially decaffeinated.
The direct solvent method, born of Roselius’ serendipitous accident, this method involves hydrating green coffee beans, either by steaming or immersion, and then rinsing them repeatedly with either of the two solvents discussed previously. The solvent comes into direct contact with the green beans in the bathing solution and extracts the caffeine while leaving all other components of the coffee mostly unaffected. The solvent passes over the beans multiple times becoming replete with caffeine. After around 8 – 12 passes, the coffee reaches the required caffeine level (97% must be removed to reach US standards, 99.9% for their European counterparts) and the solvent is distilled, removing the caffeine. The coffee is then cleansed with clean water and dried.
The Indirect solvent method uses these same chemicals to treat the water the beans are bathed in. Instead of the chemicals directly coming into contact with the beans, the green beans are themselves soaked in hot water for a number of hours. The beans are then removed and it is at this point that either ethyl acetate or dichloromethane are added to the slurry and the caffeine removed by evaporation. The same water used in this batch is then cycled through multiple batches of beans. After several cycles, this water reaches a state of equilibrium, whereby the water and the beans have a similar chemical profile, and therefore no flavor compounds are lost. The flavor-full water is then used to rehydrate the coffee beans and the beans are subsequently dried.
The Water Process is known primarily by two brand names, Swiss Water and Mountain Water. Much like the indirect solvent method, the beans start off their path to decaffeination in a bath of water. The water process manufactures uses the term ‘GCE’, aka Green Coffee Extract, to describe the slurry of water-soluble coffee compounds. Both the Swiss Water method and the Mountain Water method use patented filters to enable the extraction of caffeine from the GCE, by way of the migration along a gradient from the caffeine-rich green beans into the stable GCE, which lacks caffeine. As the GCE is saturated with the other water-soluble coffee compounds, only the caffeine molecules migrate from the green beans to the GCE. The other water-soluble compounds remain in the green coffee.
The filter systems both companies use are patented (Swiss Water uses activated charcoal filters), therefore so are the process names, but the methods themselves present as fairly identical to the consumer. But something that consumers, roasters, at least, will definitely notice, is the fact that because the water process method uses no solvents and tends to be rather inefficient in its use of resources, the coffee produced is usually more expensive than coffees decaffeinated using either of the solvent methods.
The Supercritical CO2 Method is another solvent-free process of decaffeination. In this process, green beans are steamed, but then added to a high-pressure vessel wherein a mixture of water and liquid carbon dioxide is circulated at 150F. At 300 atm of pressure, CO2 becomes a liquid, as dense as water, but far less viscous. The highly pressurized CO2 liquid’s viscosity, or lack thereof, allows it to penetrate the cell structure of the coffee bean and dissolve the caffeine.
This method of decaffeination is rather like performing gamma knife radiation surgery; it leads to a highly specific, targeted molecule removal. The flavor compounds, then, remain intact, while the caffeine is removed by the pressurized liquid. The CO2 is then moved to another vessel, more water is added to facilitate the scrubbing of any remaining caffeine from the CO2. Once this stage is complete, the CO2 is reintroduced into the original vessel.
This method is used in far less frequency in specialty coffee, as the cost of production is excessively expensive, especially as the water methods speak more to consumers, as well as produce far more flavorful results. This decaffeination method needs a highly specific plant to process the coffee, whose construction and operating costs and extremely high. In order for these plants to remain in operation, they need to process several thousand tons of coffee annually (numbers usually seen in the commercial/commodity coffee industry) just to stay in business. While some specialty coffee is still decaffeinated this way, it is cost-prohibitive for most importers or roasters.
The Triglyceride Method is rarely seen in specialty coffee. This process is much like the water process, but instead of using water, much like the name suggests, lipids are used instead.
The green coffee beans are soaked in either a heated water or coffee solution, they are then transferred to another vessel, where they are submerged in oils derived from spent coffee grounds. After they have soaked in this liquid for a number of hours at high temperatures, the triglycerides will have removed the caffeine but left the flavor compounds intact. The beans are then removed from the oils and dried. The caffeine is removed from the oils and these oils are then recycled and used to decaffeinate subsequent batches.
Decaf coffee drinkers make up about 12% of the market, with dual drinkers (those who drink both caffeinated and decaffeinated beverages) becoming more visible and numerous. It behooves us as an industry to bear that in mind when choosing and preparing decaffeinated coffee. We are used to decaf being regular coffee’s poor cousin. But if we choose quality coffees, treat them with care and respect, roast them with effort and specificity, we will end up with a far superior product, and a more delicious way to finish our day, as well as start it!