The Anaerobic Coffee Process

July 20, 2022

by Eric Thompson

Coffee processes can be so in-depth and alter the flavor of our treasured bean so much. Do we want something clean and tart or smooth and chocolaty? Different processes affect different flavor profiles. What in these processes alter the nuances in the final cup? The answer to the anaerobic coffee process is simply fermentation.

The word anaerobic means that the system lacks oxygen, coming from the original Greek, meaning ‘without air.’ It stems from a French winemaking method of the same name. In the other methods, oxygen is present. Here, though, it is a painstaking and arduous task to make sure that the environment that which fermentation is taking place is a fully oxygen-deprived space.

The anaerobic process can be used in conjunction with the other methods. Depending on how the cherries are dried, you can have anaerobics that are washed, natural, and honey.
It may be important to understand the structure of a coffee cherry first, so it may be a good idea to check our other article on the washed method. We go in-depth on the different layers of the coffee cherry.

What is fermentation?

To fully understand how the anaerobic process affects coffee, it is important to know what fermentation is. This is not an exhaustive explanation of the nuanced and complex fermentation reaction but is significantly simplified to suit our needs.

Fermentation is incredibly fascinating and expansive; it exists in so many vital areas of our world from food and drink to our gastrointestinal tract and cells. A small, yet important, distinction to understand is that yeasts are a fungus and are different from bacteria, which may also undergo fermentation. This will become important when we talk about the different kinds of fermentation processes that exist.

In coffee, much like wine, it is when yeast or bacteria that are either already present in the skin layer of our fruit or added, later on, consumes organic compounds. These organic compounds are the sugars present in the mucilage. The yeast or bacteria then produces a litany of acids, alcohol, and carbon dioxide. This reaction continues until that sugary sweet environment runs out of fuel, the moisture content drops too low, or the alcohol content raises too high that they die off.

For our purposes, we will be looking at two specific processes: Alcoholic Fermentation and Lactic Acid Fermentation. Simply, by reducing the amount of oxygen, yeasts that prefer oxygen undergoes alcoholic fermentation are restricted. In this anaerobic state, bacteria (specifically the bacterium known as Leuconostoc) that prefer a lack of oxygen undergo lactic acid fermentation producing, well, lactic acid. Lactic acid gives our coffee beans their distinct sour flavor. Yeasts continue to operate in anaerobic environments, so simple alcohols are still produced during the lactic acid fermentation process.

What Sets the Anaerobic Process Apart?

Our coffee goes into air-tight tanks, also known as vats, with a one-way valve. Into the vats go our cherries, which are de-pulped, exposing the mucilage. (Carbonic maceration is the process in which whole cherries are put into the vats.) There are two different ways that the expulsion of oxygen may be done. The first is through carbon dioxide being injected into the entire system so that there is never oxygen present in the fermentation process. Carbon dioxide is heavier than oxygen, so the carbon dioxide sinks to the bottom. The system becomes pressurized and the top layer of oxygen is released. The second is done by letting the tank build up pressure naturally by yeast producing carbon dioxide. The one-way valve is then opened, allowing just the oxygen to escape, which changes the method name to semi-carbonic.
There is much more control over the fermentation times, temperature, and pH levels. The lactic acid lengthens the fermentation times, which can bring out some extraordinarily complex flavors.

How Does this Process Affect the End Product?

The best way to take anaerobic coffee is as a pour-over! They are roasted lighter, often possessing a fruity and tart flavor profile. This coffee is generally sourer, so the milk does not mix well with it. If something is needed, adding some sugar can help make the flavors pop. You also are not going to get the same results from a commercial coffee maker. Break out your French press or V60 and get some blooms going. As always, good water chemistry is also important in yielding good coffee, so be sure that you are using the best water possible.

Try Anaerobic Coffee!

Current available anaerobic options include:
Junin Anaerobic
Catuai Anaerobic