Consumers have never been more aware of the impact of processing and the industry has never been more intentional with how coffee is processed.
All this has given rise to a literal compendium of processing terms and jargon – from Carbonic Maceration to Kenya’s ‘double fermentation’, EF2 and even just the classic Natural – what does it all mean?
In order to break it all down, we need to talk about the umbrella of processing and the traditional processing methods.
The path of processing
Coffee beans begin their processing journey as a ripe cherry and each part of the coffee cherry plays an impact depending on the processing method. A number of different compounds found in coffee contribute to the final flavor profile that you’ll enjoy in your cup.
Traditionally, coffee cherries are processed through the washed (wet) or natural (dry) methods so let’s break down what’s happening during these processes.
Washed or Wet Process
The washed process is likely the most common process found across producing countries. In a nutshell - coffee cherries have the outer skin and pulp removed, the coffee beans are soaked in tanks of water then are dried either mechanically or sun-dried.
There’s a lot more to it that that though.
Depulping
Coffee cherries are fed into a depulper which uses abrasion to separate the coffee bean from the pulp (which is the discarded as cascara and typically fed back onto farms as compost).
No changes are happening to the flavor profile at this point but unmaintained equipment can damage the coffee beans which can result in some negative attributes in the cup such as sourness through oxidization of any machine damage.
Dry fermentation
While washed coffees aren’t known for having particularly fermented flavours like their natural counterparts, washed coffees do still undergo a dry fermentation before the washing.
Depulped coffee beans are typically stored in large tubs and aerobically fermented for 24-72 hours. The primary purpose of this step is to break down the mucilage surrounding the coffee bean.
Why do producers aim to break down and remove the mucilage surrounding the coffee bean? The main reason is mold preventation.
84% of the coffee mucilage is water which, if not taken care of, can encourage mold growth on the coffee beans particularly in more humid environments.
Dry fermentation allows ambient yeasts and micro-organisms to break down the mucilage by feeding on the pectates and sugars of the mucilage.
Soaking
After the dry fermentation has lapsed, the coffee beans are soaked in water to remove the degraded mucilage – again, typically over 24-72 hours. During this time the seeds actually begin to germinate and, without the naturally occurring simple sugars of the coffee cherry, the germ begins to use up the simple sugars (fructose and glucose) present in the seed itself. This results in the common misconception that Natural coffees are sweeter due to their process whereas it’s rather that Washed coffees are made less sweet due to their process.
Drying
Once the coffee beans have been washed they are then dried until they reach an ideal moisture content (typically between 10-11 percent). Depending on the location of the farms, producers may dry their coffees using several different methods.
Concrete patios/surfaces
Patios are one of the more common drying sites due to availability. Producers are able to use roads, rooftops or specialised concrete patios to dry their coffees. While the availability and low investment means that many producers can access these, coffee lots are at risk of cross-contamination. A common contaminant are loose pieces of concrete which is why many medium to large scale roasters install destoning machinery.
African raised drying beds
Unsurprisingly originating from Africa, these raised drying beds are now common in most producing countries. The raised beds were designed to tackle the issues of space and airflow that standard concrete patios were plagued with. The fine mesh bottoms allowed for better drying of coffee cherries/beans by allowing air access to the bottom of the pile which would otherwise be at risk of mold with concrete patios. The design also allows multiple beds to be stacked, freeing up space for other coffee lots.
Guardiola/mechanical dryer
Common amongst large producing countries such as Brasil and Colombia, mechanical dryers will typically dry coffee lots over the course of three days as opposed to one week or more. These dryers allow larger volumes of coffee to be processed even while it's humid or raining. The drawbacks of these dryers are the initial costs of the equipment and the drying process itself. Coffees that are dried down to 10-11% moisture content over a short amount of time tend not to retain their quality compared to lots that are dried over longer periods.
Milling and sorting
While not part of processing per say, coffee is milled at different points depending on the process. Washed coffee is sent to a milling station once dried where the parchment surrounding the beans is removed through a huller. Finally, depending on the station, coffee can be sorted through density, screen size and colour.
A snapshot
Washed process coffees are particularly common in Latin America due to the availability of water compared to African countries. The washed process is also considered more desirable amongst farmers due to it's lower labour costs (producers aren't having to frequently tend to natural coffees); space efficiency (as naturals take longer to dry, they occupy a lot of space) and desirable flavour profile. Washed coffees are known for having a clean cup and sweetness with a pleasant acidity.
Washed process variations
The Washed process is a broad term for coffees that have had their pulp and mucilage removed before any form of drying. However, with coffee processing being such a complex procedure, there are many variations appearing from the classic washed process.
Double soak or Kenya soak
At certain origins, in particular Kenya, the coffee beans are double soaked in fresh water. This process is carried out for a couple of reasons but the primary reason is due to space constraints and air temperature. In Kenya, where space is limited and air temperature is high, coffee lots are occasionally backlogged and waiting for drying space to become available before they are able to be dried themselves. Rather than leaving the coffee exposed to the heat where they are at risk of mold, producers began storing the already washed coffee in water tanks. What this process contributes to the final flavour profile has not yet been determined but many hypotheses include a cleaner cup profile, more defined flavours and a higher quality texture.
Anaerobic washed
The anaerobic washed process focusses on fermenting in a low-oxygen (hence anaerobic) environment. This is typically done during the dry fermentation phase - depulped coffee beans are stored in a sealed bag (often GrainPro) and allowed to dry ferment in the anaerobic environment. This anaerobic variation on dry fermentation draws out the step to an average of 4 days as the lower oxygen level slows down the fermentation process.
Lactic washed
The lactic washed process is technically a style of anaerobic washed. The emphasis is on the type of bacteria that anaerobic promotes - lactobacillus.
This group of bacteria are present in high concentrations in anaerobic environments and favour cherries with high sugar content. The higher concentration of lactobacillus and, subsequently, higher concentrations of lactic acid within the coffee beans present a silky, creamier body and sweetness in lactic washed coffees.
Stay tuned for our next breakdown - Natural Coffees