What is the Relationship Between Pour-Over Coffee Concentration and Extraction Rate? Solutions for Overly Concentrated Pour-Over Coffee

Introduction

Today's pour-over coffee is predominantly made from lightly roasted single-origin beans with floral and fruity notes. Sometimes, after brewing a cup of aromatic coffee that smells delightful, you might find the flavor unclear and difficult to distinguish upon tasting, resulting in an uncomfortable sensory experience. However, after adding 10-20ml of water to the coffee, the flavors become clear and well-defined.

Bitterness from High Concentration Is Not Necessarily Over-Extraction

Beginners often directly associate uncomfortable bitterness in coffee with over-extraction, but this is not entirely accurate. First, let's understand what extraction rate and concentration represent.

The extraction rate refers to the proportion of substances extracted from coffee beans. Approximately 30% of coffee bean components are water-soluble, and an extraction rate of 18-22% is considered reasonable. Extraction rates above 22% carry the risk of over-extraction.

Concentration generally refers to the content of substances in coffee liquid. The concentration of pour-over coffee is not typically high, usually remaining below 2%.

The relationship between these two is connected through "water" - how much water we use during brewing to extract "how many substances from the coffee grounds." "How much water" is what we commonly call the brew ratio, while how much coffee substance water extracts as a proportion of the total liquid is the coffee concentration.

For example, in a coffee brewing experiment conducted by FrontStreet Coffee, we brewed Ethiopian Gedeb beans using a 1:15 brew ratio. The concentration test showed 1.49%, and the calculated extraction rate was 19.66% (within the 18-22% range and at the lower end of this interval), completely within the reasonable extraction range. However, upon tasting, the flavor was unclear with a slight bitter sensation. Subsequently, we added 20ml of purified water to the coffee and stirred it evenly. The concentration test showed 1.22%, and upon retasting, the bitterness was significantly alleviated, while the berry acidity, honey sweetness, and fermented notes became clearly distinguishable, enhancing the overall taste bud experience.

Why Does This Happen?

First, human sensory perception is complex and selective about flavors, just as we cannot resist sugars but reject eating plain white sugar directly because its purity is too high, causing an overwhelming sweetness. The same applies to fruit juice concentrate - drinking it directly feels uncomfortable, but becomes pleasant and delicious when diluted with water.

The flavors in coffee are complex, combining sour, sweet, and bitter notes. If the concentration is too high, flavor compounds become too concentrated, making it difficult for taste buds to clearly distinguish flavors, while also bringing astringency and excessive bitterness. Adding water doesn't change the overall substances in the coffee liquid; it only increases the space between molecules, making it easier for taste buds to identify other flavors.

The Trend Towards Lower Concentration Coffee

For previously popular dark roast pour-over coffee, people preferred the rich mouthfeel of high concentration (although there isn't a strong direct relationship between mouthfeel and concentration, in reality, mellow coffees typically have high concentrations). Today's light roast pour-over coffee, however, uses higher brew ratios to express the coffee's flavors, with more people leaning toward 1:16 or even higher ratios, presenting a cup of coffee that is light and flavor-rich.

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