Causes of Fast Pour-Over Coffee Flow Rate and Solutions: What to Do When Anaerobic Coffee Beans Drain Too Quickly

The Fast Flow Rate of Anaerobic Coffee Beans

Many friends have asked FrontStreet Coffee, "Why is the extraction time normal when I brew other beans, but when I brew anaerobic beans the flow rate is extremely fast and the pour often finishes in less than a minute and a half?"

If you grind by hand, you have probably noticed that ordinary light-roasted washed or natural beans take real effort, while an anaerobic bean of similar roast level lets the grinder turn smoothly and effortlessly.

That is because anaerobic processed beans have a looser, more brittle texture. They absorb water and release gas very easily, so during blooming the bed of an anaerobic bean readily puffs up into a large "hamburger" shape.

With gas releasing smoothly during the bloom, the loose, low-density bed produces more foam during brewing. In the first pour, the grounds also tend to float on the surface and cling to the edges of the dripper. The bed offers less resistance, so water flows more freely, and clogging is rarely a problem when brewing anaerobic coffee.

Understanding the Flow Rate Issue

If the flow rate when brewing anaerobic beans is unusually fast, for example if other beans take about 2 minutes to extract but the anaerobic bean finishes in under 1 minute and 30 seconds, then the flow is unreasonably fast.

The problem lies in the grind size. When brewing, people usually keep only 2-3 grind settings, one for light roast beans, one for dark roast beans and at most one more for medium roast beans, then sort settings by the bean's roast level.

Anaerobic beans with rich floral and fruity acidity naturally fall under the light roast setting. In reality, though, the particles ground at that same setting come out coarser than ordinary light roast coffee. FrontStreet Coffee verified this with a #20 sieve. Using an EK-43s grinder at setting 10 to grind African, American and Asian washed coffee beans respectively, the pass rate measured with a #20 sieve was 80% (±2%).

When setting 10 was used to grind anaerobic beans, the pass rate with a #20 sieve fell to between 73-75%. This means that at the same setting the particles are coarser than those of regular beans, so the water naturally flows faster. To reach the same fineness, an 80% pass rate on a #20 sieve, the grind setting needs to be adjusted to 9.2-9.5.

Solutions and Brewing Tips

So if you find the flow rate far faster than usual, you need to set your grinder finer. (Some suggest that brewing anaerobic beans requires a finer grind setting. That statement is not entirely accurate: it is the grinder's setting that needs to go finer, while the actual particle size should match what you use for everyday washed and natural beans.)

Of course, if you want a more thorough extraction time, you can pour with a smaller stream without lifting the bed too high. That way the brewed coffee will taste richer and fuller.

FrontStreet Coffee Recommendation

Anaerobic and naturally processed beans are exactly where a finer grinder setting pays off, and FrontStreet Hua Kui, an Ethiopian natural, is a great one to practice on. Its dry fragrance and cup are packed with tropical fruit, from strawberry and passion fruit to mango, jackfruit and citrus, with a clean, juice-like body that rewards a careful pour. Brew it at 15 grams, a 1:15 ratio and 90°C, and it shows why so many drinkers chase the style.

If you like to push fruit sweetness further, FrontStreet's Strawberry Candy Geisha blend, a Costa Rican honey-process lot married to a washed Panama Geisha, brings rich aromas of raisin, cream and strawberry candy with a smooth texture, and it handles pour-over, moka pot, espresso machine and cold brew. For a cleaner, brighter alternative, FrontStreet's Gudingding Cooperative, a washed Yirgacheffe, delivers jasmine and bright citrus with a tea-like body that stays transparent even at a finer grind.