chocolate covered coffee beans

coffee: the nectar of the gods

Sunday, September 10, 2006

Coffee processing

Processing of coffee is the method converting the raw fruit of the coffee plant (cherry) into the commodity green coffee. The cherry has the fruit or pulp removed leaving the seed or bean which is then dried. While all green coffee is processed the method that is used varies and can have a significant effect on the flavor of roasted and brewed coffee.

A coffee plant usually starts to produce flowers 3-4 years after it is planted, and it is from these flowers that the fruits of the plant (commonly known as coffee cherries) appear, with the first useful harvest possible around 5 years after planting. The cherries ripen around eight months after the emergence of the flower, by changing colour from green to red, and it is at this time that they should be harvested.

Coffee berries are most commonly picked by hand by labourers who receive payment by the basketful. As of 2003, payment per basket is between US$2.00 to $10 with the overwhelming majority of the labourers receiving payment at the lower end. An experienced coffee picker can collect up to 6-7 baskets a day. Depending on the grower, coffee pickers are sometimes specifically instructed to not pick green coffee berries since the seeds in the berries are not fully formed or mature. This discernment typically only occurs with growers who harvest for higher end/specialty coffee where the pickers are paid better for their labour. Mixes of green and red berries, or just green berries, are used to produce cheaper mass consumer coffee beans, which are characterized by a displeasingly bitter/astringent flavour and a sharp odour. Red berries, with their higher aromatic oil and lower organic acid content, are more fragrant, smooth, and mellow. As such coffee picking is one of the most important stages in coffee production, and is the chief determinant for the quality of the end product.

Wet process

Sorting coffee in water
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Sorting coffee in water
Coffee drying in the sun. Dolka Plantation Costa Rica
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Coffee drying in the sun. Dolka Plantation Costa Rica

Most of the world's green coffee has gone through some sort of wet processing including most of the premium coffee.

After the Green coffee is picked the coffee is sorted by immersion in water. Bad or unripe fruit will float and the good ripe fruit will sink. The skin of the cherry and some of the pulp is removed by pressing the fruit by machine in water through a screen. The bean will still have a significant amount of the pulp clinging to it that needs to be removed.

In the ferment and wash method of wet processing the remainder of the pulp is removed by breaking down the cellulose by fermenting the beans with microbes for several days and then washing them with large amounts of water. Fermentation can be done with extra water or in "Dry Fermentation" in the fruit's own juices only.

In machine-assisted wet processing fermentation is not used to separate the bean from the remainder of the pulp rather it is scrubbed off by a machine.

After the pulp has been removed what is left is the bean surrounded by two additional layers, the silver skin and the parchment. The beans must be dried to a water content of about 10% before they are stable. Coffee beans can be dried in the sun or by machine but in most cases it is dried in the sun to 12-13% moisture and brought down to 10% by machine. Drying entirely by machine is normally only done where space is at a premium or the humidity is too high for the beans to dry before mildewing. When dried in the sun coffee is most often spread out in rows on large patios where it needs to be raked every six hours to promote even drying and prevent the growth of mildew. Some coffee is dried on large raised tables where the coffee is turned by hand. Drying coffee this way has the advantage of allowing air to circulate better around the beans promoting more even drying but increases cost and labor significantly. The parchment is removed from the bean and what remains is green coffee.


Dry process

Dry process, also known as unwashed or natural coffee, is the oldest method of processing coffee. The entire cherry after harvest is placed in the sun to dry on tables or in thin layers on patios. It will take between ten days and two weeks for the cherries to completely dry. The cherries need to be raked regularly to prevent mildew while they dry. Once the skin is dry, the pulp and parchment are removed from the bean. While coffee was once all dry processed it is now limited to regions where water or infrastructure for machinery is scarce. The supply of dry processed coffee is very limited, with coffee from the Harrar region of Ethiopia and some areas of Yemen and Brazil being the primary sources.