Notes from the Fruity Frontier of Fermentation: The Latest in Coffee Processing
Coffee Fermentation is a Natural, Long Standing Process
Fermentation happens. It has always been a fact of processing coffee for market and consumption.
Even before the advent of wet milling with fermentation tanks, perhaps 300 years ago, chemistry was happening inside the coffee cherry after it was picked and during drying. With or without the introduction of water into the process, microorganisms (aka little tiny tiny single-celled alchemists like yeast, bacteria, and fungi that can only be seen with a microscope) are busy transforming organic substances like pectins, starches and sugars inside the coffee cherry into something else, like acid and ethanol, that can be absorbed by the bean.
In fact, under the right conditions, fermentation can begin before the coffee cherry is even picked. When humidity is high, coffee can over-ferment if not depulped soon after picking.
Although fermentation during the wet milling of coffee has a long history (with many variations in process), the focus of fermentation was primarily to loosen the mucilage clinging to the bean so that washing could be more easily and thoroughly accomplished. In 1922, William Ukers wrote:
“Whether coffee is washed or not, it has to be dried; and there is a kind of fermentation that goes on during washing and drying, about which coffee planters have differing ideas, just as tea planters differ over the curing of tea leaves. Careful scientific study is needed to determine how much, if any, effect this fermentation has on the ultimate cup value.”
In-depth analysis of controlled fermentation and experimentation to positively affect cup quality is a relatively recent development and largely coincides with the rise of the specialty coffee industry. Fermentation interventions, or augmentations, are just a few years old.
Fermenting Coffee with Fruit
One of the most recent processing innovations in the specialty coffee industry is fermenting coffee with fruit, literally introducing fruit and/or fruit juices into green coffee processing.
Coffee producers have moved from experimentation to solid success with a variety of methods of coffee fruit fermentation, including carbonic maceration, where coffee cherries are sealed in containers and the oxygen removed using C02. This method of fermenting coffee with fruit opens up a whole world of possibilities with specialty coffee – adding fruit flavors and notes to premium green coffee.
Fruit Fermentation can also include adding sliced or smashed fruit to honey processed coffee as it is turned during drying. A wide variety of fruit or friends of fruit, like wine yeast, have been used. We've been able to cup coffees from our producer partners in Colombia that have been fermented with grapes, oranges, wine yeast, passionfruit and more.
Some of the fruit “partnerships” result in such pronounced flavors they are easily identifiable even by those without professional coffee tasting credentials, sometimes even before they taste the coffee. The unmistakable aroma of grape fills the air as coffee fermented with grapes spills from the grinder.
When it comes to understanding the science of fermentation in coffee processing, with fruit or without, much remains to be explored as producers continue to push processing boundaries. Fruit fermentation might not be everyone’s cup of coffee, but for those of us who enjoy exploring different and new, innovations in processing will continue to deliver.