With the harvesting season nearing its end, we have a bit of catching up to do with our series about processing. This time I want to take about the step following the harvest, in Yunnan being wet processing. Siphon tank with cherries (water is recycled) After harvesting, the cherries either go directly to the pulper (when the harvest is well done) or they are collected in a siphon tank filled with water. In this siphon tank the cherries are cleaned and separated. Stones sink to the bottom of the tank and are removed manually when the tank is emptied. The lighter cherries will float on top of the water and are removed through a weir along with leaves and twigs. The cherries which are suspended in the water column are recovered by a siphon and moved towards the pulper. Pulper (back) and fermentation tanks The objective of pulping is to separate the pulp from the parchment beans. This pulp is torn off by squeezing the cherries. As ripe cherries contain a lot of water, the parchment beans will pop out easily when the cherries are squeezed. The next step is to remove the mucilage, which aims at removing the residual part of the mesocarp that remains stuck to the endocarp after pulping (also see this post on the parts of a coffee cherry). As the mucilage is insoluble in water and clings to the parchment too strongly to be removed by simple washing, it is removed by either fermentation followed by washing or by strong friction in so-called mucilage removers. Fermentation of parchment coffee In Yunnan this process mainly takes place through natural fermentation. The term fermentation is not 100% correct as no biochemical reaction takes place inside the coffee bean. It would be more correct to refer to the process as removal by means of biochemical reaction or hydrolysis of the mucilage. This reaction is caused by enzymes which are naturally present in the coffee cherries. The duration of fermentation can vary from 6 to up to 72 hours, depending on the temperature, the amount of mucilage, and the concentration of peptic enzymes. The coffee is kept in the fermentation tanks until the mucilage is completely digested and the beans are ready for washing. It is critical for coffee quality to stop the fermentation at the right time as over-fermentation causes the formation of so-called stinkers. If fermentation is deficient or too slow, butyric acid or propionic acid can develop, both of which have an undesirable effect on coffee quality. The fermented parchment coffee has to be washed immediately after the fermentation process is completed in order to stop this process. It is however possible to soak the parchment coffee in clean water for 12 to 24 hours after removing the mucilage and before washing, in order to reduce the bitterness and harshness of the beverage.
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AuthorI wouldn't be surprised to find out I was born with a passion for coffee. For the life of me, I can't remember not loving coffee. And by that, I don't just mean drinking it, but everything involved from its cultivation over the processing to the final product that is my loyal companion throughout the day. Archives
February 2014
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