Post-harvest coffee processing and how it translates to what you taste in your cup
You might have noticed that we always give you ‘the process’ for every coffee on our labels. Ever wondered: ‘What is coffee processing and why does it matter?’
Well this is where we shed some light on the topic.
Let’s start with the basic anatomy of the coffee plant. What we know as ‘coffee beans’ are really the seeds of the coffee cherry. Coffee cherries grow on a beautiful shrub-like tree with large, waxy, dark green leaves and amazingly fragrant, bright white flowers which turn into the fruits containing the seeds that we roast, grind, brew and enjoy as coffee.
The seeds are surrounded by the pulp, which is the fleshy part of the cherry and then a sticky layer of 'mucilage' that firmly clings to the seed itself. Underneath the mucilage there is a protective layer of parchment skin which serves to shield the seed.
The steps involved in getting from the coffee cherry on the tree to the green coffee that is packed in bags and shipped from origin to the doorstep of our roastery are what we refer to as ‘coffee processing’.
Harvest
The first step is getting the cherries off the tree. There are three ways to get the job done:
Machine harvest – big machines drive through neatly planted rows of coffee trees usually on big plantations and just get all the fruit harvested indiscriminate of whether they are ripe, unripe or overripe.
Stripping – coffee pickers go through the rows of trees and strip off all the fruit branch by branch – fairly indiscriminate of degree of ripeness
Selective picking – coffee pickers go from tree to tree and hand select only the ripe coffee cherries and leave the unripe fruit on the tree to continue maturing
For the best quality coffee, you want only the perfectly ripe cherries since these will provide the best flavour. In the specialty coffee sector most coffees will have been selectively picked – which is as you can imagine more time- and labour-intense and thus more expensive. But ultimately worth it because of the increase in quality and price the coffee farmers can achieve.
Processing
Natural or Dry Processing
To produce natural or dry processed specialty grade coffee, the coffee cherries are sorted for ripeness after harvest and put out on concrete patios or raised netted beds to dry in the sun for days.
Fermentation sets in due to naturally occurring yeasts and bacteria in the
cherries metabolizing sugars and acids. The fruit pulp is broken down and dries out. To avoid overfermentation the cherries have to be moved and turned every couple of hours.
It is usually good to have the option for shade in regions where direct exposure to the sun at high temperatures all day long can cause overfermentation. This processing method doesn’t require water, which can be a sparse good in some coffee growing region. It is however more labour-intense because of the tossing and turning of the cherries.
Resulting flavour profile: Naturals are sweet with a heavier body and have more berry-like and chocolatey aromas. Blueberry or strawberry aromas are especially sought after in natural coffees. It’s not unusual to get a slightly fermented ('farmyard') flavour in the cup.
Fully Washed or Wet Processing
With washed coffees, the cherries are run through a depulping machine where the fleshy part is mechanically removed and only a sticky layer of mucilage remains around the seeds. The coffee seeds (‘beans’) are left to ferment in water tanks where, again thanks to yeasts and bacteria, the mucilage is broken down and fermentation occurs. However due to the immersion in water in combination with the removal of the fruit pulp, the fermentation is much less aggressive and affects the seeds in slightly different ways.
After they have been given one last wash in clean water, the seeds are then moved into the sun to dry and loose moisture. The washed process requires large amounts of water, as well as equipment and machinery. It is more cost and resource-intense but requires less manual labour. In many coffee growing regions especially in Africa, communal ‘washing stations’ are set up and run by farmer cooperatives to share these costs.
Resulting flavour profile: Washed coffees have a much more brilliant acidity; they are more fruity with an overall complexity and cleanness to them. It’s not unusual to find aromas of tropical fruits, stone fruits or even hints of floral notes in these types of coffee.
Pulped Natural or Honey Processing
Pulped natural or honey processed coffees are somewhere in between naturals and washed coffees. After the harvest, the cherries are sorted and depulped with different degrees of fruit pulp remaining on the seed (the different degrees of pulp remaining correspond with different ‘colours’ of honey process, ranging from white to black). But instead of being fermented in water, the depulped seeds are immediately dried in the sun. The fermentation process that occurs is more aggressive than in the water tanks but less aggressive than with the entire cherry drying in the sun.
The advantage here is that the water usage is minimal and only a fraction of the equipment required for washed coffee is needed for honey processing.
Resulting flavour profile: Honey processed and pulped natural coffees are usually sweeter than washed coffees but cleaner with a more complex acidity and juiciness than natural coffees. And so if done right, they combine the best of both worlds.
No matter the processing, once the coffee is dried to a moisture content of 10-12%, it is milled to remove any residual layers of either mucilage or parchment skin and we are left with the green coffee bean ready to be shipped and roasted.
Here is the best visual summary of the entire journey of the 'coffee bean' by Dan Zettwoch:
Source: Dan Zettwoch for The University of Michigan's college of Literature, Science & The Arts magazine, the Spring 2012 "Food" issue