How to Identify Over-Extracted Pour-Over Coffee and Solutions for Adjustment

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Understanding Coffee Extraction

When freshly roasted coffee beans are ground into small particles and combined with hot water, they release a large amount of soluble coffee flavor compounds. These dissolved flavor compounds constitute the different textures we experience when tasting coffee.

Over-extracted coffee means too many soluble substances have been extracted from the coffee, resulting in undesirable flavors.

In a single coffee bean, 70% is woody fiber and 30% is soluble substances. Among these, approximately 20% are positive flavor compounds, while about 10% are bitter and negative substances. Therefore, a delicious coffee with well-balanced flavors should have an optimal extraction rate of 18-22%.

Different flavor compounds dissolve in water at different speeds and times. Generally, positive substances are extracted first, while negative flavor compounds require longer time to dissolve.

Typically, sweet and sour flavor molecules have smaller molecular weights, making them easier to extract with hot water, while bitter and unpleasant flavor molecules have larger molecular weights and are extracted during the middle to later stages.

If only the smaller molecular weight substances are extracted without the larger ones, the coffee will have noticeable sweet and sour flavors but lack body and taste thin. Additionally, without the balancing effect of bitter compounds, the coffee becomes sharply acidic. FrontStreet Coffee refers to this situation as under-extraction.

If both the smaller molecular weight substances are extracted and too many larger molecular weight substances are released, the coffee's sweet and sour flavors will be masked by bitterness, while simultaneously exhibiting a dry, astringent sensation that's difficult to swallow. FrontStreet Coffee refers to this situation as over-extraction.

Factors Affecting Coffee Extraction

Based on FrontStreet Coffee's years of brewing experience, there are two main causes of over-extraction: high brewing water temperature and coffee ground too fine. The extraction rate of substances also varies among coffee beans with different roast levels.

According to FrontStreet Coffee's roasting observations, coffee beans with shorter roasting times and lighter roast degrees typically have smaller density after roasting, making it more difficult for flavor compounds to release in water.

Therefore, when brewing light to medium roast coffee beans, FrontStreet Coffee recommends using medium-fine grind/fine sugar size (75-80% pass-through rate with China #20 standard sieve), combined with 90-91°C water temperature for extraction.

Meanwhile, medium-dark to dark roast coffee beans, due to extended roasting time and reaching the second crack, will have relatively looser structures, making substances easier to release in water.

Therefore, when brewing dark roast coffee beans, FrontStreet Coffee recommends using medium-coarse grind/coarse sugar size (65-70% pass-through rate with China #20 standard sieve), combined with 88-89°C water temperature for extraction.

Extraction Rate Variations

FrontStreet Coffee has found in actual brewing that, depending on the coffee bean's variety, processing method, roast degree, and other factors, some coffees may have extraction rates below 18% and, while somewhat flat, exhibit very clear flavors; others may have extraction rates above 22% and, while strong in taste, don't present noticeable astringency. In these cases, FrontStreet Coffee prefers to describe them as "low extraction" or "high extraction."