Decaffeinated coffees used to have a bad reputation which means that even today many people think of decaf coffees as having no taste, or even a bad chemical taste. But thankfully times have changed, and modern speciality decafs use the same types of high-quality coffee beans and remove the caffeine using far gentler and less toxic methods than earlier decafs resulting in more of the rich flavour compounds remaining in the coffee.
Sugar cane method
The earliest form of decaffeination was invented by Ludwig Roselius and involved soaking coffee beans in sea water and then extracting the caffeine using benzene which was later found to be carcinogenic. Thankfully this toxic chemical is no longer used. These days the solvent used is ethyl acetate which is either derived as a by-product of sugar cane processing or artificially manufactured in a lab. The coffee beans are first steamed then rinsed with the ethyl acetate several times before being steamed again to remove the ethyl acetate. This results in 97-99% of caffeine being removed while leaving the flavour and aroma compounds intact. This method does impart some flavour of its own, adding a brown sugar flavour that works well in coffees that naturally have a smooth taste such as most South and Central American coffees but less well in those that have a more fruity acidic taste like many African coffees.
Swiss Water method (sometimes called mountain water method)
This is one of the most popular methods of decaffeination as it is chemical-free and is allowed under organic certification. It uses water saturated in green coffee extract which contains all of the water-soluble compounds that are naturally present in coffee. This is produced by soaking coffee beans in hot water and then passing the water through an activated charcoal filter that removes the caffeine molecules. The coffee beans that are being decaffeinated are then soaked in the extract, and has it is saturated with all of the molecules apart from caffeine, only the caffeine diffuses out of the beans leaving them caffeine-free. This method removes some of the flavour, although it is constantly improving.
CO2 decaffeination
In this process, green coffee beans are steamed before being added to a vessel where they are exposed to water and CO2 under high pressure and heat. The heat and pressure transform the CO2 to a supercritical fluid where it has properties between water and gas, allowing caffeine to dissolve in to it. Most of coffee’s flavour and aroma compounds are insoluble in CO2 and so they remain in the coffee beans. The decaffeinated coffee is then washed with water to remove the CO2. This method tends to be more expensive so is not as commonly found. It is said to remove some of the flavour comparable to the Swiss Water method
Methylene Chloride / Dichloromethane process
This is a very low cost process compared to other methods and preserves most of the original coffee flavour, but it is not typically used to decaffeinate speciality coffees because the chemical is toxic, being linked to several cancers as well as other health harms. The main risk of exposure is for those working in the decaffeination process where inhalation and skin contact can cause serious problems. It evaporates at fairly low temperatures and so by the time it has been processed and roasted there is very little left of it on the coffee but we prefer not to purchase coffees using this method. If coffee is simply labelled as decaf but no method is mentioned, this tends to be the method used because less toxic methods, particularly the Swiss Water method tend to be advertised as a selling point.
How does decaffeination affect the taste of coffee
Modern decaf processes minimise the removal of flavour and aromatic compounds, resulting in a flavour that is close to the original bean. However, caffeine itself has a flavour, adding a bitterness that can be pleasant when balanced against other sweet flavours. Caffeine is even added to cola and other soft drinks specifically for this bitterness. Roasting slightly darker can counteract this a little by adding in bitter burnt toast notes from the roasting process. We don’t roast very dark because we like the natural flavour of each bean to shine through, but decafs tend to roast slightly darker before they crack (expand and release sugars near the end of the roasting process) anyway so this works out well for the flavour.
What is your favourite decaf method? Have you found any differences between the different styles?