Why does coffee process change the flow rate when brewing?

Anaerobically processed coffee beans can drain faster than expected during brewing, even at a grind size that suits a medium roast, and the cup can taste thin. The cause lies in the cellular structure: low-temperature, oxygen-free fermentation leaves the bean's cell walls looser and its roasted interior more porous.

Anaerobic processing places ripe cherries in sealed containers at 10 to 15 degrees Celsius, slowing pulp and pectin breakdown and raising sweetness. Front Street's brewing tests with beans such as Rose Valley and Mozart show the faster flow, and suggest adjusting grind setting and pouring technique to restore aroma and body in the cup.

Many coffee enthusiasts encounter a puzzle when brewing anaerobically processed coffee beans: even when they follow the grind standard for a medium roast, the water flow is noticeably too fast, and the resulting coffee tastes thin and lacks complexity. Behind this phenomenon is, in fact, a close relationship with the changes that anaerobic fermentation brings to the cellular structure of coffee beans. This article starts from Front Street Coffee's actual brewing tests, combines the grind sieve-passing rate data of anaerobically processed beans such as Rose Valley and Mozart, analyzes the causes of the faster flow rate, and offers adjustment suggestions in both grind setting and pouring technique, to help you reproduce at home an anaerobically processed coffee with full aroma and a smooth mouthfeel.

Introduction

Many friends have asked Front Street Coffee this question: when brewing anaerobically processed beans at home, they use the grind size corresponding to a medium roast, but the water drains especially fast, and the brewed coffee always has a kind of "watery," thin feel... Which step exactly is going wrong? Below, let's talk about how the parameters should be adjusted when brewing anaerobically processed coffee beans.

What is the anaerobic processing method?

The anaerobic processing method involves placing freshly picked ripe coffee cherries into sealed containers for low-temperature fermentation, with the temperature maintained between 10 and 15 degrees Celsius. Under these low-temperature, oxygen-deficient conditions, the decomposition process of the pulp and pectin is slowed down, thus extending the fermentation period and ultimately allowing the coffee beans to display a more pronounced sweetness.

The changes brought by anaerobic processing are not limited to increased sweetness; the density of the coffee bean cell walls also changes. For example, for similarly high-altitude, strictly hard beans from Central America, compared with traditional processing, anaerobically processed beans have a somewhat looser cellular structure, and after roasting, the interior of the beans is also more porous.

What parameters should we adjust when the flow rate is fast?

If the water flow is found to descend too quickly during brewing, the first thing to check is the grind size. When Front Street Coffee brews medium-roast beans, it usually uses an EK43S #10 setting (the coarseness of most medium-roast beans at this setting can achieve an 80% passing rate on the Chinese standard No. 20 sieve). So if the same setting is used to grind anaerobically processed beans, can they also reach an 80% sieve-passing rate?

Front Street Coffee selected two anaerobically processed beans from different producing regions in Central America and ground them at an EK43S #10 setting. Front Street Coffee Costa Rica Musician Series Anaerobic Honey Process Mozart Coffee Beans had a sieve-passing rate of 76% after grinding; Front Street Coffee Colombia Finca El Arbol Double Anaerobic Washed Rose Valley Coffee Beans had a sieve-passing rate of 77% after grinding.

When brewed after grinding at the EK43S #10 setting, Front Street Coffee Mozart Coffee had a brew time of 1 minute 47 seconds, with flavors of raisins, a slight fermented note, and the sweet-tartness of pineapple, but a weak finish and an overall thin body; Front Street Coffee Rose Valley Coffee had a brew time of 1 minute 45 seconds, with flavors of roses and the sweet-tartness of berries, but only sweet-tartness, and it was likewise overall thin.

Although the sieve-passing rate was already close to 80%, the beans themselves had a loose structure, the water flow rate was somewhat fast, and the flavor compounds had not yet been fully extracted. So Front Street Coffee adjusted the grind finer to EK43S #9.5. After the adjustment, the sieve-passing rate of Front Street Coffee Mozart Coffee Beans rose to 81%, and Front Street Coffee Rose Valley Coffee Beans reached 82%.

When brewed after switching to grinding at the EK43S #9.5 setting, Front Street Coffee Mozart Coffee had a brew time of 1 minute 57 seconds, with flavors of a dried-fruit-like fermented note, orange blossom aroma, berry sweet-tartness, and a pineapple finish, with a clear aroma and a smooth mouthfeel; Front Street Coffee Rose Valley Coffee had a brew time of 1 minute 55 seconds, with flavors of rose and white peach aromas, berry sweet-tartness, and a finish like liqueur chocolate, with a prominent aroma and a full body.

If the flow rate is still fast after adjusting the grind size, what is the reason?

Then you need to check whether the pouring speed is too fast. No matter which dripper is used, Front Street Coffee recommends controlling the flow at about 4 grams per second, while keeping the water flow steady and poured vertically into the coffee bed.

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The above content is compiled by CoffeeHunters, a coffee news website.