If you’re into the weird and wonderful when it comes to coffee, Anaerobic Coffee Processing is a new term you might have seen cropping up on coffee bags recently, including our own La Chumeca!.This process, also known as Anaerobic Fermentation, is a new method some producers have been implementing to seek out new and exciting flavours in a coffee. All coffee undergoes a period of fermentation once it is picked but by making some adjustments in this vital stage, a coffees flavour profile can completely change.
Fermentation in Coffee Processing
Fermentation takes place when yeast and bacteria in the coffee cherries mucilage start to convert acids and sugars into organic acids, CO2, ethyl alcohol and other compounds. Fermentation will differ depending on whether a coffee is washed, natural or honey processed.
Producers use different techniques to control this process such as water tanks, water channels, buckets, raised beds and patios. Fermentation finally stops when the coffee reaches 11% moisture content. This is known as Aerobic Fermentation as it takes place in the presence of oxygen.
Anaerobic Fermentation is when oxygen is removed from the tanks or buckets that coffee cherries sit in during fermentation. Valves are used to allow oxygen to escape and regulate the pressure in the sealed tanks.
Because oxygen is present in Aerobic coffee processing, oxidation can speed up fermentation. Anaerobic Fermentation on the other hand allows coffee to ferment slowly resulting in a more complex flavour profile that forces more fruit flavours from the cherry into the bean. Different acids are also developed at this stage like lactic acid which give the coffee a bright, almost sparkling characteristic.
Anaerobic coffee processing can incorporate natural, washed or honey depending on whether the coffee is fermented with the cherry on, de-pulped or in mucilage. Fermentation in the pressurised tanks takes between 40-120 hours after which it is dried to the right moisture level.
During Fermentation Brix Degrees, temperature and PH levels are constantly monitored. This is something that Martin Ureñs Quirós atLa Chumecahas mastered as a way to help prevent any unpleasant ferment flavours developing and achieve a certain sweetness and acidity after 96 hours of fermentation.
This season we’re roasting his Anaerobic Natural, meaning cherries are intact during the fermentation process. This gives us an extra heavy mouthfeel which is countered with a vibrant kiwi like acidity and a strawberry yogurt note. We’re now down to the last sacks of this unique coffee so give it a try before its gone and keep your eyes peeled for more exciting processes to come.