How to Read a Coffee - Part 3: Processing & Fermentation

By Dale Harris & Alex Scott

Coffee beans are the roasted seed of the coffee fruit, and the different processes used to remove the fruit layers impact the final flavour of a coffee. Processing is a big subject, and we are currently living through an explosion of new techniques and unique approaches, designed to impact and differentiate flavour, making categorisation harder than ever before. Most of these can be placed on two spectrums, one between the most traditional ‘natural’ or dry processing, and ‘washed’ or wet processed coffees, and a second based on the level of technical intervention shaping that process.

From Natural to Washed

In a traditional ‘natural’ process, cherries are picked, sorted and then dried in the sun on patios or raised beds over 3-6 weeks, during which the fruit dries, and falls off, leaving the green seed in a protective layer ready for hulling and export. Coffees processed this way tend to have higher body, and a deep sweetness caused by fermentation and the migration to the bean of some compounds. Coffees processed this way may sometimes have dominant boozy or funky flavours, that some customers love, and others may not, but a good barista knows what to ask to figure out who to recommend these wilder coffees to.

In a traditional ‘washed’ process, cherries are picked and taken to a wet mill for sorting, and depulping, where the cherry skin is broken, and the coffee ferments in a tank (with or without soaking) where enzymatic and fermentation processes break down the remaining fruit. This is then washed off, before the seeds are dried in the sun for a few weeks before final milling and export. Washed coffees tend to exhibit higher acidity, cleaner flavours and greater clarity than their natural counterparts.

Due to the high water use in washed coffees, particularly with older technology, some regions embraced hybrid processes - honey, and pulped-natural process coffees sit somewhere in between ‘natural’ and ‘washed’, where a percentage of the fruit is removed before drying to allow for some of the benefits of dry processing, without as many risks. 

Because ‘natural’ processing carries a higher risk of mould and related flavour defects, as well as fermentation flavours that some markets dislike, coffee produced by quality focused farmers have historically been washed to protect and retain the unique qualities of their terroir and variety. With more market awareness and interest, more high quality naturals are produced from many regions that used to only export washed coffees, and it’s common for farms with the capability and resource to offer both washed and natural lots, as well as hybrid processes.

Contemporary Processes

The other spectrum, which we can call higher intervention, can be applied to any of the above processes. These can range from adding specific yeasts or cultures at fermentation stages, and/or regulating these cultures through creating anaerobic or anoxic fermentation conditions through use of sealed tanks, specific temperature and ph control mechanisms, or adding fruits and sugars at initial fermentation stages. Higher intervention techniques may add dominating flavours from processing that can obscure terroir and variety characteristics. 

A particular trend in high intervention processes at the moment are “co-fermented” coffees. These are advertised as having natural fruits added during the fermentation process, adding bold unmistakable fruity flavours. However there is evidence to suggest many of these beans are actually using artificial flavourings; if your coffee tastes like foam bananas, or blueberry, watermelon or grape candy consider how rare those fruits have those flavours -  It’s probably not coming from actual fruits. 

That’s not to say these coffees can’t be tasty, or there is anything wrong with enjoying them. Our personal choice as a roaster, is to celebrate the diversity of coffee flavour we believe comes from the combination of plant, soil, climate and farming skill, and potential additives can obscure those conversations.

How to Taste it

At Ithaka, we tend to lean away from particularly process heavy coffees, but that doesn't mean we don't have great examples of coffees that typify the techniques used. Below is a selection of coffee that we feel show off the best characteristics of various processing methods. Click below to learn more, or ask about them at our tasting bar in Digbeth.