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

Anyone who has brewed anaerobically processed coffee knows the experience: compared with conventionally processed beans, the water races through the bed. "Whoosh" — and it's gone. Brewing time for anaerobic beans always misses the target by a wide margin.

Set a target of around 2 minutes and conventionally processed beans hit it perfectly. Apply the same parameters to anaerobic beans, however, and the brew wraps up around 1.5 minutes — sometimes even sooner. The result tastes watery and thin, the classic signature of under-extraction. So why do anaerobic beans drain so fast?

The answer lies in the special fermentation behind the process. Anaerobic processing seals freshly harvested coffee in closed containers to ferment without oxygen, steering the flavor development in a chosen direction.

During anaerobic fermentation, the beans absorb large amounts of sugars, which boosts their sweetness significantly. But the density of their cell walls changes too, and with all that sugar attached, the beans undergo more intense chemical reactions during roasting. The upshot: at the same roast level, anaerobically processed beans come out with a more porous structure. Take the same variety processed both ways — the anaerobic batch roasts to a lower density, with a crumblier texture and higher brittleness. At the same grind setting, those beans shatter into coarser particles with bigger gaps between them, and because they saturate more easily, the water simply flows through faster. To extract them properly, then, we need more contact time between hot water and grounds — in other words, slow the flow down.

How to Extend Extraction Time

There are many ways to stretch extraction time: reduce the pour flow, add more pour stages, grind finer, or switch to a slower-dripping brewer. FrontStreet Coffee recommends adjusting the grind first.

The other methods all introduce extra variables that muddy the diagnosis — and for beginners, complicated operations only make brewing harder. Adjust the grind first; only if that still doesn't produce a good cup should you fine-tune further based on what the taste tells you.

Take FrontStreet Coffee's own practice. For traditionally processed light-to-medium roast beans, we primarily use setting 10 on the EK43 grinder — roughly an 80% pass-through rate on a No. 20 sieve. On the same setting, anaerobic beans only reach about 75% pass-through, because their extra brittleness makes them break into coarser particles. Brewing an anaerobic natural Sidra this way took just 1 minute 35 seconds, and the flavor was flat with a thin mouthfeel.

We then adjusted one setting finer, to 9.5, which pushed this anaerobic Sidra above 80% pass-through on the No. 20 sieve. Sure enough, the brew ran 1 minute 54 seconds, and the flavors came through not only full-bodied but exceptionally sweet. If the coffee still shows under-extraction after the grind adjustment, raise the water temperature or slow the pour flow slightly to lift extraction efficiency and correct the flavor. Over-extracted? Simply reverse the moves — lower the temperature, speed up the flow, and so on.

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FrontStreet Coffee Recommendation

Anaerobic and other fruit-forward naturals tend to be roasted light to medium, so a well-chosen medium roast makes a great companion brew. If you like neither sourness nor bitterness, FrontStreet Coffee's Brazil Queen Estate is the easy pick: a Yellow Bourbon from the world's largest coffee-producing country, medium roasted to bring out creamy peanut, chocolate, toast, and sugarcane notes in a quiet, sweet cup — at home in a pour-over, moka pot, or espresso machine alike.

Want your medium roast sweeter and fruitier? Try our Strawberry Sugar Geisha blend, which marries a honey-processed coffee from Costa Rica with washed Geisha from Panama. Medium roasted to showcase the best of both, it pours with orange-blossom honeyed aroma and rounded sweetness, and works beautifully as a cold brew, pour-over, or espresso. And for a balanced classic, our Jamaica Blue Mountain No. 1 — medium roasted to fuse gentle acidity, bitterness, sweetness, and body into chocolate, roasted nut, cream, and caramel flavors — remains the benchmark that other coffees struggle to match.