Introduction:The flavor of pour over coffee is often influenced by the extraction process. Once the parameters are off, unpleasant tastes such as sourness, bitterness, and astringency can easily emerge. This article delves into the causes of over-extraction and under-extraction, analyzing in detail how factors such as water temperature, grind size, coffee-to-water ratio, and extraction time affect coffee performance. Using several representative pour over beans as examples, it provides practical parameter suggestions to help you adjust your brewing method more precisely and brew a well-balanced cup of coffee.

Flavor imbalance in pour over coffee often stems from improper extraction control. Over-extraction leads to bitter, astringent, and muddled flavors, while under-extraction results in thin and sharp-tasting coffee. Understanding the essence of extraction and mastering key parameters is the first step to brewing great coffee.

Extraction refers to the process of dissolving flavor compounds from coffee grounds using water. Simply put, it’s about using hot water to draw out the aromatic components hidden within coffee beans, forming the flavors we taste. When this process is well-controlled, it delivers a balanced and rich mouthfeel; otherwise, it can swing to extremes—either overly harsh or bland.

Over-extraction occurs when too many soluble substances, especially large-molecule bitter and astringent compounds that typically dissolve later in the brew, are released into the coffee liquid. Such coffee often brings out bitterness, astringency, and even some unpleasant off-flavors, resulting in an overall poor taste.

There are three main causes of over-extraction: First, too long an extraction time—when coffee grounds are in contact with water for too long, undesirable compounds from the later stages are excessively extracted, affecting overall flavor. Second, excessively high water temperature, especially for medium to dark roasted beans such as Indonesian Mandheling (with spicy and caramel notes), Brazilian Queen Estate (showcasing roasted peanut and cream aromas), and Jamaican Blue Mountain (chocolate and nut flavors)—it’s recommended to keep the water temperature between 86–88 degrees Celsius to avoid over-extracting bitter compounds. Lastly, grind size that is too fine—if the coffee grounds are as fine as flour, water flows through more slowly, and if extraction time exceeds two minutes or the coffee bed turns muddy, it’s necessary to adjust the grinder to a coarser setting to ensure the coffee liquid drips through smoothly within two minutes.

In contrast to over-extraction, under-extraction happens when coffee grounds and water are in contact for too short a time, or extraction conditions are insufficient, resulting in the inadequate dissolution of desirable flavor compounds. Such coffee usually has a light body, lacks complexity, and may sometimes carry raw astringency or sharp acidity, resulting in an unbalanced overall profile.

Common causes of under-extraction include: a grind size that is too coarse, preventing effective flavor extraction; water temperature that is too low, failing to fully activate aromatic compounds in the coffee; and additionally, a coffee-to-water ratio that is too high—i.e., too much water poured—can also lead to an under-extracted state where the coffee appears concentrated but is actually flavor-poor.

For medium to light roasted beans such as Natural Huakui, Emerald Estate Green Label Geisha, and Kenya Little Tomato—these beans from high-altitude regions are harder in texture and their flavor compounds are harder to release. It is recommended to use a grind size akin to superfine sugar and set the water temperature between 91–93 degrees Celsius to ensure sufficient heat and fine grinding help extract the flavors. At the same time, pay attention to the coffee-to-water ratio and pouring rhythm to avoid over-dilution leading to incomplete extraction.

In summary, to brew a pour over coffee with balanced flavors, the key lies in precisely controlling the four essential elements: water temperature, grind size, coffee-to-water ratio, and extraction time. Observe changes in flow rate and color during the brewing process, and adjust the parameters accordingly, to avoid issues of over-extraction or under-extraction, and truly enjoy the diverse layers of coffee flavor.

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