How is Coffee Decaffeinated?

 

We have recently added decaffeinated coffee to our small but very select range of speciality coffees that we offer.  We cannot discriminate against those who have to make those decisions and why should we, therefore we will continue to stock a single estate decaf for those that love the coffee but without the caffeine.

Now that we have added decaf coffee to our list of coffees that are available then naturally we are being asked about the process.  How is the caffeine removed?  There have been so many documentaries on TV recently about coffee that the interest is beginning to stir.  One of those documentaries was about the removal of caffeine and the process described was the ‘Direct Solvent Method’.  It will no doubt have been quite worrying for some people that this process existed and that the coffee was being immersed in chemicals to strip the caffeine out.

Given that this was on national TV, then there is now a perception that this is the only way of removing caffeine from the coffee bean.  I put this post together really to illustrate that there are other processes to remove the caffeine than the one documented on TV, and to try and explain how each method works.

For info, and reassurance, the coffee that we roast has been through the CO2 process, NO CHEMICALS WERE USED to remove the caffeine.  This is one of the cleanest methods that are available and we would use no other way.

Just to begin with here are 10 facts about caffeine which you may find surprising:

  1. A cup of coffee (8oz, or 240ml) will typically contain around 95 milligrams of caffeine
  2. Decaf coffee will still have traces of caffeine left, typically around 2 to 5 milligrams (in some cases still up to 20mg)
  3. A can of Cola will have approximately 30 to 35mg caffeine
  4. A 240ml can of Red Bull will have 80mg of caffeine
  5. A cup of tea will have approximately 26mg caffeine per 240ml
  6. Robusta coffee will have approximately twice as much caffeine as the Arabica varietal
  7. Roasting coffee darker actually reduces the caffeine content, therefore the opposite is true, light roasts have more caffeine
  8. There are about 60 plants that actually contain caffeine
  9. Caffeine affects the nervous system, and thats why we love it or loathe it so much
  10. Caffeine is the common name that we all know, though its systematic name is 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione (remember that!!)

Method 1: The Direct Solvent Method

I have touched on this already so therefore it is the most appropriate place for us to start.

This process is fairly straightforward.  The beans are steamed to expand the bean, giving it a greater surface area and therefore making it easier to extract the caffeine.  The coffee beans are then soaked directly in a solvent to remove the caffeine.  The solvent that is typically used is Methylene  Chloride.  After this process the beans need to be dried, this involves draining away the solvent and then steamed which aids the evaporation of what solvent is left on the bean.

The damaging nature of this product is the reason why we will not endorse this process as a means to strip caffeine from your coffee.  In this example, it is something that we have the capacity to control, so therefore we opt for the safer and more environmentally friendly option.

Method 2: The Indirect Solvent Method

This method is a similar process to the direct method, however, in this instance the bean does not come into direct contact with the solvent.  The caffeine, which is soluble in water, is extracted by soaking the beans in water.  Many of the flavours and the oils are also extracted during this process, so the solute is treated with Methylene Chloride and then returned to the beans to reabsorb the falvours.

This process is by far the most commonly used method by the main commercial roasters.  The reasons for this are pretty overwhelming; it is cheap, effective and reliable.

The one thing that is worth adding to this debate is that for those that are concerned about the health effects of drinking decaf coffee derived from the solvent methods (Methods 1 & 2), then I would not be too concerned.  Solvent is in their very nature have low boiling points.  Methylene Chloride has a boiling point of 39.6°C.  So given that after the decaf process the green beans are then steamed (~100°C), and then subsequently roasted to ~ 200°C temperatures, and then of course immersed in hot water when it is eventually consumed, then the likelihood that this solvent, with a boiling point of just 39.6°C, will still be present in the bean to actually be digested by the end user is extremely unlikely.

If however, that you prefer not to endorse this method for environmental reasons, this is a very different story.  Methylene Chloride is synthetically manufactured chemical produced by the likes of DOW Industries, PPG and AkzoNobel.  Therefore the reason to be mainly concerned about with this process is indeed the impact to the environment.  This impact has got to be considered for the full lifecycle of this chemical from manufacture (energy, byproducts, spillages, CO2 etc) to disposal (Incineration, evaporation etc), and these all of course have a detrimental effect on the environment.

Note: sometimes the chemical used in this is Ethyl Acetate, which can occur naturally; and this process is named “Natural Decaf”.  However, the quantities needed for this process mean that the chemicals used for this are still synthetic.

Method 3: CO2 Method

This method is a very clean and selective method to remove the caffeine.  The process that the bean goes through is much less invasive and consequently the results are remarkable.

The start of this process is similar to many others, the beans are immersed into water to mobilise the caffeine.  However, in this particular method CO2 is introduced at high temperature and pressure (~50°C and ~100Barg).  This CO2 is selective therefore only draws out the caffeine from the coffee beans; no other elements are removed using this process, preserving the integrity of the coffee as much as possible under the circumstances.

The CO2 which is rich in Caffeine is then washed with water to remove the caffeine.  The water now is caffeine rich, so this just needs to be dried in order to successfully remove and isolate the caffeine.

CO2 is repressurised and is recycled back into the process.

Note: CO2 as we know it exists mainly as a gas.  It can, as any gas, be compressed and cooled enough to turn it into a liquid.  However, the CO2 that is introduced into this process is a “Super Critical Fluid”, where really the thing doesn’t know how it should be existing, so it is existing as both liquid and gas, simultaneously.  It is when the CO2 is in this state that the decaffeination process can occur.

Method 4: The Swiss Water Process

This is another natural method where there are no chemicals involved.  This process again uses water to remove all of the caffeine but of course we know that water alone is not selective.  In addition to stripping out the caffeine it is also stripping out the flavours and the oils.  This solute is then passed through a carbon filter where the caffeine is stripped from this caffeine rich solution.  The oils and flavours are returned back to the bean after going on this full circle journey.  By subjecting these essential elements of the coffee to this process, then damage does still occur and the flavour of the coffee will of course be effected by this.  Of course this method is still preferable to the MC processes, it is simply worth noting that the process is not completely selective.

There is in fact a nice little video on the Swiss Water Process which explains quite well how the process works.  Embedded below:

 

 

As mentioned previously, the processes that your roaster will use will essentially it all comes down to cost, efficiency and reliability (but mainly cost) and it is an unfortunate fact that this is how the world operates.  We want everything but we are not prepared to pay for it.

As a micro roaster, then we can afford to be that little bit more selective.  We pay a premium for our coffees as we want to directly trade with the farmers and our customers who buy from us also buy into our policy.  The decaffeinated coffee that we roast has all been removed using the CO2 method.  We pay a slight premium for this service, but that is a choice that we have made and we are proud to be in a position to be able to do so.

Written by David Beattie of Rounton Coffee

 

1 Comment

  • I am not sure where you are getting your info, but great topic.
    I needs to spend some time learning much more or understanding more.
    Thanks for great information I was looking for this info for my mission.