For casual coffee fans, reviewing processing methods on the side of a bag of coffee might seem like a bit of a stab in the dark. Aren't all coffee beans natural? Why would it be necessary to wash coffee beans? Won't honey make it a bit too sweet?
If you've ever been in this scenario, don't worry. As opaque as they may seem at first, basic processing methods, once explained, are easy enough to understand. But what do they mean for the flavours that end up in your cup? And what pioneering methods are taking speciality coffee to the next level?
In this blog we'll cover the basics on processing and the types you're most likely to see, as well some rarer examples you might not have heard of before. Each brings their own unique characteristics to your cup, so if you can, be sure to grab some of each and sample the difference for yourself!
What does 'processing' in coffee actually mean?
Let's start with definitions. 'Processing' isn't in the roasting, in the growing or in the brewing, processing in fact occurs after the beans have been harvested, but before they're shipped for roasting.
Processing pertains specifically to the removal of the coffee cherry's pulp, fruit, mucilage, parchment (basically everything but the bean) before it is dried and sent for roasting. However, just as there's supposedly more than one way to skin a cat, there are several ways to do process, and these pertain to when and how the cherry's flesh is removed. Let's look at them in more detail.
Natural
Perhaps the best method to start with is natural, which involves letting the bean dry 'naturally' with the cherry's flesh left on. One of the oldest methods of processing, this seemingly rudimentary method requires meticulous attention to detail.
Through this process, the beans will begin to ferment, and, in doing so may ferment unevenly or excessively, making for unpleasant flavours or simply, coffee that is unfit for human consumption due to the formation of mould based mycotoxins.
However, if dried successfully through frequent turning, the natural sweetness of the cherry's flesh will be allowed to seep into the now dried bean. Once the flesh is removed with a de-pulper or hulling machine, you're left with beans that are characteristically bold and fruity in flavour. Some examples of
Washed
Washed process coffee sits on the other end of the spectrum from natural processed coffee. Immediately depulped to remove the outer layer, the beans, still with mucilage attached are then submerged in water to remove the remaining flesh. Farmers may experiment with submersion times on future beans to tweak their flavour to their liking.
These beans are then given a final rinse before being sun-dried on a flat surface. This results in beans that produce a clean, crisp and slightly acidic flavour profile, with some even describing the mouthful and flavour as 'tea-like', offering a wholly different drinking experience to a natural coffee.
Honey
Our final stop on our journey through the three common processing methods, honey processing presents an appealing balance between the richness of natural, and the clarity of washed.
Sometimes referred to as 'pulped natural', honey processed coffee, like washed processed, begins its journey by being immediately depulped, leaving behind the mucilage. However, divergence occurs whe,ninstead of immediately removing the remaining mucilage, the beans go through an initial drying process with the residual flesh still present, before a final rinse. To explore different flavour profiles, growers may experiment with different drying times, resulting in what's referred to as yellow, red and black honey/pulped natural processed coffees.
This results in a coffee that has a less-pronounced acidity than natural processed coffees, while still retaining the fruit flavours that people love and recognise them for.
What is Experimental Processing?
Experimental processing is the term given to a processing method outwith the traditional methods, washed, natural & honey.
These processes generally involve forms of extended fermentation that add layers of complex flavours to the profile of the coffee. Often the processes are adapted from methods out with the coffee industry, such as wine making. With this experimentation, the farmer also adds a layer of risk to their crop.
Because these processes are untested, the farmer has no way of knowing if the coffee will score highly, or if the crop will spoil, resulting in great financial impact to the farmer. However, as demand for these coffee grows amongst coffee drinkers around the world, the more boundaries farmers are pushing to achieve the most unique and funky cup of coffee.
Now that you know the basics, let’s take a deep dive into some of the most popular experimental processes.
Anaerobic Fermentation
All coffee undergoes some form of fermentation during processing. What separates Anaerobic fermentation from basic fermentation, is the removal of oxygen from the equation. To carry out an Anaerobic Fermentation, intact or de-pulped coffee cherries are sealed in containers with water for a pre-determined length of time before they are dried. This process rapidly changes the flavour of the coffee, leading to more complex flavours than traditional fermentation.
Thermal Shock
We know a thing or two about this process thanks to the incredible coffee we currently have from Yenni Esperanza. The coffee is picked at 95% maturity and then washed using ozonated water and ultraviolet light. The coffee then undergoes an anaerobic fermentation in a steel tank for 48 hours at 18°C, before being pulped, and then undergoing a further 48-hour anaerobic fermentation at 21°C. Finally the coffee undergoes a heat shock to eliminate any micro-organisms and is then machine dried by air circulation for 12-28 hours at 34°C.
Carbonic Maceration
Taking it's name from a wine making process common in the Beaujolais region of France, this process first hit the spotlight in 2015 when Saša Šestić used it in his World Barista Championship routine.
For this process, the coffee cherry is places inside a sealed container before being flushed with carbon dioxide. Anaerobic Fermentation & Carbonic Maceration are both quite similar in the sense that they are both low oxygen environments, the only difference is that with Carbonic Maceration, the initial fermentation must take place inside the cherry with the addition of carbon dioxide.
Ice Fermentation
Another experimental process that we're getting familiar with thanks to the sensational coffee from Jairo Arcila. Ice fermentation is a relatively new, experimental processing method that was developed by coffee producer Jairo Arcila and his sons and co-owners of Cofinet, Felipe and Carlos Arcila.
This coffee was exposed to a dry aerobic fermentation of 24 hours. Fermentation begins as soon as a coffee is picked, due to the presence of water, sugar, bacteria, and yeast.
Leaving the fruit on the coffee during this phase allows for the sugars and acids in the coffees mucilage to convert into different sugars, acids, CO2, ethyl alcohol, and other compounds.
Imparting sweet and fruity flavours on the coffee, the beans are then placed inside grainpro bags for 50 hours, maintaining a temperature below 22 degrees while fermentation continues. Afterwards, the coffee is frozen for 72 hours, before being placed on raised beds below 35 degrees to thaw and dry until ideal moisture content is achieved.
So there you have it: your guide to all things coffee processing! This is by no means a comprehensive list, with innovation moving rapidly, there is a constant flow of new processing methods making their way to market with each new harvest. One thing is for sure, there's never been a more exciting time to be a fan of speciality coffee.
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