Why Do Anaerobically Processed Coffee Beans Drain So Quickly? How to Extend a Short Extraction Time?

Anyone who has brewed anaerobically processed coffee knows this experience well: compared to conventionally processed coffee beans, the water flow during brewing of anaerobic processed beans is exceptionally fast. "Whoosh!"—the water just flows right through. Consequently, the brewing time for anaerobically processed coffee beans always deviates significantly from our target brewing time!

For example, when we set our target brewing time at around 2 minutes, conventionally processed coffee beans brew perfectly to this standard. However, when we apply the same parameters to anaerobically processed beans, the brewing time gets stuck at around 1.5 minutes, or even completes extraction in less than 1.5 minutes! The resulting coffee tastes watery and lacks richness—clear signs of under-extraction! This naturally makes people wonder: why do anaerobically processed beans flow so quickly?

This brings us to the special fermentation method of anaerobic processing! Anaerobic processing involves placing freshly harvested coffee beans in sealed containers for anaerobic fermentation, thereby guiding the coffee's flavor development in the desired direction.

During anaerobic fermentation, coffee beans absorb large amounts of sugars, significantly enhancing their sweetness. However, the density of their cell walls also changes due to this processing. Moreover, because of the sugar attachment, the beans undergo more intense chemical reactions during roasting. Therefore, after anaerobic processing, at the same roast level, the coffee beans' structure becomes more porous. For instance, the same variety of beans, when processed anaerobically versus conventionally, will have lower density after roasting, with a crumblier texture and higher brittleness. This means that with the same grind setting, anaerobically processed beans will produce coarser particles with larger gaps between them. Additionally, because they saturate more easily, the brewing water flow for anaerobically processed beans is consequently faster. Therefore, we understand that to achieve proper extraction from anaerobically processed coffee beans, we need to increase the contact time between hot water and coffee grounds—in other words, slow down the water flow.

How to Extend Extraction Time

There are many ways to extend extraction time, such as reducing pour flow rate, increasing the number of pour stages, grinding finer, or switching to a slower-dripping brewer. FrontStreet Coffee recommends prioritizing grind adjustment.

This is because other methods introduce more variables that can affect judgment. For beginners, complex operations actually increase brewing difficulty. Therefore, grind adjustment should be the first priority. Only after grinding finer and still not achieving good results should we consider more nuanced adjustments based on taste discrepancies.

Take FrontStreet Coffee as an example: when brewing traditionally processed light-to-medium roast beans, FrontStreet Coffee primarily uses setting 10 on the EK43 grinder, which converts to approximately 80% pass-through rate on a #20 sieve. However, when using this same setting for anaerobically processed beans, the pass-through rate is only about 75% because the beans are more brittle and break more easily, resulting in coarser ground particles. With such coarse particles, brewing an anaerobic natural processed Sidra took only 1 minute and 35 seconds, producing a flat flavor with thin mouthfeel.

FrontStreet Coffee then adjusted the grind one setting finer, to 9.5, ensuring this anaerobically processed Sidra achieved over 80% pass-through rate on the #20 sieve. As expected, this brew took 1 minute and 54 seconds, and the extracted flavors were not only full-bodied but also exceptionally sweet. If after adjusting the grind, the coffee still shows signs of under-extraction, we can slightly increase extraction efficiency by raising water temperature or reducing pour flow rate, thereby correcting the coffee's flavor. If over-extraction occurs, we simply reverse these adjustments—such as lowering water temperature or increasing flow rate, and so on.

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