The Science Behind Anaerobic Fermentation in Rose Valley Coffee Beans: Why Anaerobically Processed Coffee Extracts Quickly

Introduction

Many friends have asked FrontStreet Coffee why, when brewing anaerobically processed coffee beans at home, even though they use the grind size appropriate for medium-roasted coffee beans, the water flows too quickly, and the resulting coffee always feels watery... Where does the problem lie? This article will explain how we adjust parameters when brewing anaerobically processed coffee beans.

What is Anaerobic Processing?

Anaerobic processing involves placing fresh coffee cherries in sealed barrels for low-temperature fermentation, with temperatures controlled between 10-15 degrees Celsius. In the low-temperature anaerobic environment, the decomposition rate of pulp and pectin decreases, extending the fermentation time and allowing the coffee beans to develop more sweetness.

In addition to increased sweetness, anaerobically processed coffee beans also undergo changes in the tightness of their cell walls. For example, when comparing Strictly Hard Beans (SHB) from high-altitude regions of Central America, anaerobically processed beans have a less dense cellular structure compared to traditionally processed beans. After roasting, the internal structure of anaerobically processed coffee beans becomes more porous.

What Parameters Should We Adjust When Water Flows Too Quickly?

When experiencing fast water flow during brewing, the first consideration is the grind size. FrontStreet Coffee typically uses EK43S setting #10 when brewing medium-roasted coffee beans (most medium-roasted beans at this setting achieve an 80% pass rate through a Chinese standard #20 sieve). But can anaerobically processed coffee beans ground at the same setting achieve an 80% sieve pass rate?

FrontStreet Coffee tested two anaerobically processed coffees from different Central American origins using the EK43S #10 setting. FrontStreet Coffee's Costa Rica Musician Series Anaerobic Honey Mozart beans achieved a 76% sieve pass rate, while FrontStreet Coffee's Colombia Big Tree Estate Double Anaerobic Washed Rose Valley beans achieved a 77% sieve pass rate.

When brewed at the EK43S #10 setting, FrontStreet Coffee's Mozart had a brewing time of 1'47" and displayed flavors of raisin, light fermentation, pineapple's sweet-tart balance, with a weak aftertaste and overall thin body. FrontStreet Coffee's Rose Valley had a brewing time of 1'45" and displayed rose and berry sweet-tart notes, with only sweet-tart sensations and an overall thin body.

Although the sieve pass rates were close to 80%, the beans' inherent porous structure caused fast water flow, preventing sufficient extraction of flavor compounds. Therefore, FrontStreet Coffee adjusted the grind size to EK43S #9.5. After this adjustment, FrontStreet Coffee's Mozart beans achieved an 81% sieve pass rate, while FrontStreet Coffee's Rose Valley beans reached 82%.

When brewed at the EK43S #9.5 setting, FrontStreet Coffee's Mozart had a brewing time of 1'57" and displayed dried fruit-like fermentation notes, orange blossom aroma, berry sweet-tart balance, pineapple aftertaste, with pronounced aroma and smooth mouthfeel. FrontStreet Coffee's Rose Valley had a brewing time of 1'55" and displayed rose and peach aromas, berry sweet-tart balance, chocolate liqueur aftertaste, with pronounced aroma and full body.

What If Water Flow Remains Too Fast After Adjusting Grind Size?

It could be that the pouring speed is too fast! Regardless of which dripper is used for brewing, FrontStreet Coffee recommends controlling the water flow at 4g/second while maintaining a stable, vertical flow into the coffee bed.

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