Introduction:Do you often encounter a trace of annoying burnt bitterness or off-flavors when brewing pour over coffee, even when using high-quality beans? This is likely caused by over-extraction. This article delves into the scientific principles and practical reasons behind over-extraction—including key parameters such as water temperature, grind size, and pouring time—and provides specific adjustment suggestions and high-tolerance brewing strategies to help you avoid bitterness and brew a well-balanced, clean cup of coffee.

Many pour over enthusiasts have had this experience: carefully selected coffee beans that, when brewed, end up with a noticeable burnt bitterness or chaotic astringency, significantly diminishing the overall flavor of the cup. This situation is commonly referred to as “over-extraction.” But what exactly is over-extraction, and why does it happen? This article will take you from the root to understand the causes of over-extraction, analyze how various brewing parameters affect flavor, and offer practical solutions to help you easily steer clear of the bitterness trap and brew smoother, more balanced pour over coffee.

First, we need to understand that when people say a cup of coffee is “over-extracted,” they usually mean it tastes noticeably unpleasantly bitter—especially that kind of burnt or rough, harsh bitterness. However, not all bitterness comes from over-extraction. For example, intense bitterness caused by an overly high coffee-to-water ratio does not fall under the category of over-extraction. The truly uncomfortable over-extracted bitterness is usually accompanied by thin flavor and an unclean aftertaste.

To explore the causes of over-extraction, we must go back to the so-called “Golden Cup Extraction Theory.” This standard proposed by coffee scientist Dr. Lockhart indicates that only about 30% of the soluble compounds in coffee beans can be dissolved by water, and when the extraction yield falls between 18% and 22%, the acidity, sweetness, and bitterness of the coffee are most harmonious, resulting in the most balanced mouthfeel. But once the extraction yield exceeds 22%, it becomes easy to extract too many undesirable impurities, which often manifest as unpleasant burnt or harsh bitterness. Although some high-quality coffees can still perform decently even slightly above 22% today, generally speaking, we still define “over-extraction” as the state where noticeable burnt and off flavors are perceived—not just based on data alone.

So, what practical operational factors lead to over-extraction? After summarizing, they can mainly be categorized into the following five points: too high water temperature, too fine grind size, too long pouring time, too much total water volume, and overly vigorous stirring during pouring. Simply put, these factors all increase the extraction efficiency of the coffee, meaning more substances (including undesirable impurities) are released into the water, thereby raising the risk of over-extraction.

For example, if the water temperature exceeds 93°C, for most coffee beans—especially medium to light roasts—it’s very easy to release subtle impurities, excessive tannins, and bitter compounds from the beans. Similarly, grinding too finely greatly increases the contact surface area between coffee and water, causing the coffee grounds to release their contents more quickly and in greater amounts. Extending the pouring time or repeatedly stirring the coffee bed vigorously can also make the extraction overly uniform and deep, further increasing the likelihood of over-extraction.

It’s worth mentioning that these parameters often do not act alone but influence each other. For instance, if you use coarser coffee grounds, you might be able to slightly increase the water temperature or extend the pouring time without over-extracting. But if you switch to an extremely fine grind, even with a lower water temperature, the overly dense contact between coffee and water may still cause over-extraction. Therefore, evaluating whether a brewing setup is reasonable cannot rely on a single parameter alone but must consider the overall configuration and operational process.

In practice, many amateur and professional brewers adopt highly personalized brewing techniques—for example, using extremely high water temperatures paired with ultra-fine grinds. While such methods may extract extreme flavors, they demand a very high level of skill, tactile sensitivity, and understanding of the coffee bean characteristics from the brewer. A slight misstep can easily lead to over-extraction issues, resulting in unpleasant harsh bitterness. This is also why, for beginners or those who hope to consistently brew good-tasting coffee, choosing “high-tolerance” brewing parameters is more practical and important.

So, what kind of parameters are considered high-tolerance? Take water temperature as an example: many professional shops set their brewing water temperature around 91°C during daily operations. This temperature is highly adaptable for most coffee beans, especially medium to dark roasts. Even if the grind is slightly coarser or the pouring technique isn’t perfectly precise, obvious over-extraction is less likely to occur. In contrast, using 93°C or even higher water temperatures may, under certain conditions, bring out richer flavors, but it also demands stricter control over fine particles, grind uniformity, and operational stability. A mistake in any one aspect can very easily produce bitter and off flavors.

Additionally, methods such as using a slow and steady circular pouring technique, selecting a moderate coffee grind size (like sugar-like coarseness), and maintaining an appropriate coffee-to-water ratio (commonly 1:15 to 1:16) are all effective ways to improve brewing tolerance. By comprehensively adjusting these parameters, you’ll be able to more easily brew pour over coffee with clear flavors, balanced mouthfeel, and no harsh bitterness.

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