BEST PRACTICES: COFFEE MUCILAGE
by Nancy Griffith
(what I have learned as of Oct 18, 2006)
After harvesting and removing the skins [pulping] of coffee cherry, the mucilage needs to be removed from the seed. The soft and slippery mucilage is actually the fruit of the coffee, as opposed to the skin and the seed. The object of fermentation is to remove sugar from the coffee in order to store coffee parchment successfully. Sugar absorbs moisture; sugar remaining on the parchment will absorb moisture, which can lead to moldy and/or putrid conditions. Pulped coffee is free of sugar when bubbles are no longer being produced in the fermenting solution. I don’t know how better to describe the mucilage free coffee except to say it feels ‘crisp’ when squished around or when you wash a little in your hand; it feels like rice or pinto beans when you wash them before cooking. I have come to be unafraid of fermenting longer than most recommendations as long as the beans still feel slippery. Last week when it was cool and raining, I fermented one batch of 500 pounds 48 hours. It smelled sweet and seems fine. Sometimes I put hot water in the vat and cover it at night to speed up the process. After a cool night you can feel areas within the fermenting beans that are much warmer than the rest of the beans; this is where yeast action is more intense.
On Kona’s small farms, the common way to remove mucilage is by fermenting the pulped cherry. Fermentation is caused by enzyme action of yeast that eats the sweet sugary fruit, usually in a fermentation vat with water to cover. The yeast always seems to spontaneously go to work on the wet coffee; nothing needs to be added to the tank. Fermentation is complete when bubbles – CO2, a byproduct of the yeast action – stop rising through the solution. The time required depends on temperature, above 80 degrees is good, up to 95 degrees is the optimum for bread and I guess it’s the same for coffee mucilage. Cooler temperatures slow the yeast action, and below 68 degrees there is very little action. Thus, the higher on the mountain you are the cooler the night and the slower the fermentation. You can start it off with warm water and cover the vat to help conserve heat. One farmer speeds things up by adding today’s pick to yesterday’s pick, which has been fermenting for 24 hours, and letting both days’ coffee ferment together. This way he gets an established working yeast action for the second day’s pick and the added volume works faster and stays warmer than two single fermentations would.
The Mechanical Demucilager
Another method of removing mucilage is with a mechanical demucilager. This is a machine that removes mucilage by rubbing beans together using little water. Often combined with a pulper, these machines are available from Captain Cook Trading Co and have capacities of 900 pounds/hour [cost about $4300 to $5000] or 2000 pounds per hour [$8000 plus $2000 for foundation, pumps etc]. Properly adjusted, they get the beans squeaky clean. Greenwell, Koa Plantation, Bob Nelson, Rick Funk and others have these demucilager machines. Coffee is pulped and demucilaged in one continuous operation and can be pumped right out to the drying deck.
Fermenting and Pulping
In contrast, fermenting is a long and labor-intensive exercise. I will tell of my own system, the one I know about. It is not ‘engineered’ for efficiency, but has been developed with thought; it is what I have been able to make basically myself. I live makai in Napoopoo where it is warmer than at 1900 feet where my farm is.
I pulp at the farm because I have a bench there that allows me to handle the heavy bags of coffee cherry. I pour the cherry into buckets then pulp into clean five gallon buckets with drain holes drilled in their bottoms and carry the coffee to my home in Napoopoo. Often I leave the buckets of coffee in the truck overnight where they begin fermenting with their own moisture.
Next I empty the buckets into a big plastic tub, holding them over the tub and spraying with water to get the last beans out. I find when I am done that this results in about the right amount of water to just cover the beans. This is good because more water means more for the fermentation process to heat up.
My fermentation tubs are at the top of a four-stage staircase, and after fermenting, I drain the fermentation liquid and beans into plastic bins with holes in the bottom. I give these a vigorous stir and rinse with the hose, and pour them into solid bottom bins the next level down for an immersion rinse where the beans are thoroughly stirred and washed. This is where I get rid of floaters. Next I pour into ‘puka’ buckets at the bottom level for a final spray rinse and drain. The coffee is now ready to lie out on the drying racks.
I estimate that pulping, fermenting and washing takes me a total of 16 hours of fairly heavy labor for 2000 pounds of cherry, plus two nights and a day for fermentation. I lift the coffee to the pulper, into the truck after pulping, out of the truck and on to the fermentation platform and into the fermentation vat. In comparison it takes to 2 hours for the small demucilager and one hour for the larger demucilager mentioned above for approximately the same amount of cherry.
Does it make a difference to the taste, the quality? Many knowledgeable people think traditional fermentation enhances the quality of the coffee, including our neighbor Bob Smith and the guru Ken David who gives the last word on coffee. A recent sample of Ken David’s prose in a review of Ethiopian Yrgacheffe coffee: ‘A light, bright breath of acidity shimmers inside an amazing bouquet of sweet jasmine and darker, woodier fragrances. The cup soars in a delicious, reeling dizziness of flowers, then immediately relaxes into spicy shadows. Somehow, all of the range and complexity remains precariously, elegantly in balance.
Yirgacheffe is a single origin washed coffee. This language leaves me in a state of reeling dizziness, I personally can’t imagine writing like this even about something I think is fabulous. But this is the kind of description our single origin Kona coffee deserves considering the inherent quality of the soil, the climate and the care we farmers take.