Introduction:Have you ever had a cup of coffee that was so bitter it was hard to swallow, making you suspect it was over-extracted? But in fact, “bitterness” isn’t necessarily synonymous with over-extraction. This article delves into the three typical sensory characteristics of over-extracted coffee—including burnt bitterness, bitter astringency, and off-flavors—and explores common brewing mistakes behind them, such as too-high water temperature, excessively fine grind size, or overly long extraction time. It also provides practical suggestions for adjusting parameters and tips on whether to keep or discard the final drips of coffee, helping you accurately grasp the extraction balance point and elevate the quality of every cup.

Many coffee enthusiasts, upon tasting a noticeably bitter cup, often immediately think, “Is this over-extracted?” However, bitterness itself cannot be directly equated with over-extraction. To understand over-extraction, you first need to know that about 30% of the soluble substances in coffee beans can be dissolved in water, and not all of these substances contribute to desirable flavors—the remaining 70% mainly consists of indigestible components like lignin and fiber. According to the industry-recognized “Golden Cup Theory” and practical experience, a coffee with an extraction yield between 18% and 22% usually delivers a better balance. Once the extraction yield exceeds 22%, we refer to it as over-extracted.

So, what specific sensory manifestations does over-extracted coffee have? They can generally be summarized into the following three common phenomena: burnt bitterness, bitter astringency, and chaotic off-flavors. These signs not only affect the taste but also often lead to misunderstandings about the coffee’s inherent quality. Next, we’ll break down the causes behind these flavor issues one by one and offer improvement suggestions.

First is burnt bitterness. It’s important to note that the “burnt bitterness” mentioned here refers to an unpleasant, charred-tasting bitterness—a type of flavor defect. Some people mistakenly believe all bitterness in coffee is bad, but in reality, the deep, rich bitterness found in high-quality dark chocolate can actually bring a pleasant aftertaste. In contrast, burnt bitterness is clearly a negative flavor, often lingering at the back of the tongue and deep in the mouth, easily causing dryness and a burning sensation. This condition mostly stems from using water that’s too hot during brewing. It is recommended to control the brewing water temperature for medium to light roasted beans between 90°C and 93°C, and for medium to dark roasts, lower it to 87°C to 89°C to reduce the risk of over-extraction.

The second common manifestation is bitter astringency. This is not just simple bitter taste perception, but rather a distinct tactile astringency that often makes the tongue feel rough and unsmooth. This kind of astringency typically comes from the excessive release of large molecular compounds in coffee—specifically “dicaffeoylquinic acid.” Such compounds not only carry bitterness but also tend to bind with proteins in saliva, thereby creating a wrinkled or rough feeling on the oral mucosa. When the content of these substances is too high, it leads to what we call bitter astringency. This situation is commonly seen when the grind size is too fine, the contact time between coffee grounds and water is too long, or there is excessive stirring during pour over. It is recommended to pay attention to adjusting these parameters during brewing.

The third sign of over-extraction is off-flavors—that is, a chaotic, unclear flavor profile, or even obvious strange or defective tastes. This is usually due to uneven heating of the coffee grounds or uneven water flow distribution during extraction, resulting in some areas being over-extracted while others are under-extracted. In practice, for example, if there is too much fine powder during pour over, it can easily create channeling effects in the filter, leading to localized over-extraction; excessive stirring can also cause hot water to concentrate in certain areas, resulting in uneven extraction and thus producing off-flavors. It is recommended to moderately sift out fine powder before brewing and maintain a stable water flow, which can help improve this issue.

Now that we understand the common manifestations and causes of over-extraction, how can we effectively avoid it? Below are two practical strategies suitable for most pour over and filter brewing scenarios.

The first is to adjust brewing parameters. After each brew, it’s recommended to observe the coffee’s flavor performance and then trace back to possible influencing factors. For example, you can check whether the water temperature used was too high or whether the grind size was too fine. As a practical suggestion, for a standard pour over using 15 grams of coffee, the overall extraction time is around 2 minutes. If you find the extraction time is too long, consider adjusting the grind coarseness or shortening the pouring time to reduce the chance of over-extraction.

Another practical tip is to discard the final drips of coffee. Since, during normal extraction, lighter molecular compounds such as acidity and sweetness are usually released first, followed by heavier ones like bitterness and impurities. Therefore, if you suspect the current extraction state may be approaching the edge of over-extraction, it’s recommended to stop collecting the coffee when there’s about 20 to 30 milliliters left in the filter—this is the tail end—and discard that portion. This helps prevent the concentrated bitterness from the final stage from affecting the overall drinking experience.

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