Control though fermentation

This month we are presenting two contrasting coffees, with very different characters brought about in part by differences in fermentation. Riakiberu uses a traditional Kenyan process, where the cherries are first depulped mechanically, as soon as they arrive at the factory. This leaves the seeds covered in a layer of fruity pulp, or mucilage. The mucilage is fermented in large tanks for between 12 and 24 hours, allowing it to be broken down so that it is able to be thoroughly ‘washed’ from the seeds, using long washing channels. Then, before drying, the cherries are taken to another set of fermentation tanks, and fermented again under water, normally for a shorter time, between 10 and 12 hours. This ‘double soak’ is popular in Kenya, and is useful not only for enhancing the cleanliness and intensity of the final cup, but also as a second opportunity to sort for lower density floating seeds, as these are often of lower quality, or from unripe cherries. This attention to detail is the reason Kenyan coffees are so consistently of very high quality, and why they carry a price premium above most other producing countries.

Meanwhile, in the remote region of Huehuetenango in North-Western Guatemala, Rosendo Domingo processes his coffee somewhat differently. Due to the remoteness of his farm, Rosendo often has trouble recruiting enough help during harvest season to help him with the complex process of picking and processing his crop. Rosendo’s solution is to dedicate his attention to picking coffee one day, and processing the next. This means that the coffee begins to ferment in cherry overnight, before it is depulped in the morning. From here, the coffee goes through the same process as at Riakiberu, depulped, fermented, washed, but with no second soak. Due to the cool temperatures high in the Guatemalan mountains, the mucilage takes longer to break down, so the fermentation is much longer, around 40 hours. This long cool fermentation, and brief pre-fermentation in cherry, leads to a much softer character in the cup, with a high sweetness, almost reminiscent of a naturally processed coffee.

Though both coffees technically use the ‘washed’ process, we hope this month to illustrate the skill and control of coffee producers as they aim to affect the character of their coffees through careful fermentation.

Stay bright and curious.
John Gibson


The Riakiberu Coffee Factory is owned by the Kamacharia Farmers Co-operative Society, established in 1994. The co-op has 1400 members, scattered throughout the area around the village of Kamacharia, where the factory is located. The factory is located at 1650 masl, in the Muranga Region, just 4 km from the border with Nyeri county. The region lies slightly further to the south of Mt Kenya than many of the more famed Kenyan growing regions, closer to the Aberdare mountain range to the west. Due to the washing process, the factory has quite a high water usage, so has to be careful with the disposal of waste water contaminated by coffee fermentation. Currently the soak pits are dug away from local water sources to avoid contamination of drinking water, but further investment will see a move towards more treatment and reuse of waste water.


Long term subscribers may recognise this coffee from last year, as this is our second year working with Guatemalan producer Rosendo Domingo. Rosendo is only 24 and took over the running of his small farm, Buena Vista, a few years ago. He is still fairly new to coffee production in general, and unlike many farmers in the region, he has no family history on a coffee farm. Therefore, he is still actively seeking to learn and improve his methods of production, in order to aim for the highest possible quality. For example, for the first two years on the farm, Rosendo was struggling to grow his coffee in naturally alkaline soil. Once he had stabilised the pH of his soils, his trees grew much healthier and stronger. Rosendo also grows several native tree species alongside his coffee, both to shade the coffee, and due to their nitrogen-fixing properties, reducing the need to spray chemical fertilisers on the farm. As we discussed, his careful processing is also an important factor in creating the beautiful soft fruit character of this coffee.  


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