Introduction:Often encounter sour and astringent thinness from under-extraction or burnt bitterness and off-flavors from over-extraction when pouring over? This guide delves into the principles of extraction, breaking down the causes of common issues step by step—from coffee beans, water temperature, grind size, pouring technique to filter choice—and provides concrete and actionable adjustment advice to help you precisely control extraction parameters and consistently brew pour over coffee with clear layers and balanced flavors.

In actual pour over practice, many coffee enthusiasts have encountered the frustration of uneven extraction. Among these, "under-extraction" often results in coffee that tastes overly acidic, thin, and with a short aftertaste; whereas "over-extraction" tends to bring out noticeable burnt bitterness and off-flavors. To improve these issues, it's first necessary to understand the basic principles of coffee extraction—the process by which soluble flavor compounds are dissolved out of the coffee grounds by water flow. According to the industry-recognized "Golden Cup" standard, an ideal pour over coffee should have a concentration between1.2~1.4 TDSand an extraction rate that falls within18%~22%. If the extraction result deviates from this range, under-extraction or over-extraction will occur, respectively. Next, we’ll analyze the causes from multiple key variables one by one and provide practical adjustment solutions.

So-called coffee extraction, simply put, is the process of allowing hot water to pass through the coffee grounds and extract the soluble flavor compounds within. In this process, many variables directly affect the final extraction outcome, including water temperature, coffee grind size, total water volume, and even the stirring method during pouring. Generally, we categorize extraction results into three types: under-extraction, ideal extraction that meets the Golden Cup standard, and over-extraction. Understanding these basic classifications is the first step in adjusting pour over parameters.

The so-called "Golden Cup extraction" refers to coffee with a concentration between1.2~1.4 TDSand an extraction rate reaching18%~22%within the ideal range. If the extraction result is below this standard, it is considered under-extraction; conversely, if it exceeds this range, it falls under over-extraction, often resulting in unpleasant flavor profiles.

Under-extracted coffee, due to the water’s failure to fully extract the soluble substances from the coffee grounds, leaves a large amount of undissolved components in the grounds. Such coffee often tastes sharply acidic, lacks sweetness, and may even carry a slight salty note, with an overall thin mouthfeel and short aftertaste. The reason behind this is that, during coffee extraction, small-molecule substances like acidity and saltiness dissolve first, followed by sweet substances, and finally bitter ones. If the overall extraction yield is insufficient, the acidic substances cannot be balanced by subsequent sweetness and bitterness, leading to overly prominent acidity and flavor imbalance.

Conversely, over-extraction is the result of too much being dissolved. Although around 30% of the substances in coffee beans are soluble, in reality, only about 20% are needed to deliver good flavor—anything beyond that can have negative effects. Excessive dissolved substances, especially the large-molecule bitter and astringent compounds released in the later stages, can make the coffee taste noticeably burnt, bitter, and off, with unpleasant astringency.

So, how should these issues be adjusted? First, many people who experience over-extraction when pouring over may be related to the roast level of the coffee beans. The darker the roast, the more caramelization products there are, and the easier it is to release bitterness during extraction. If you don’t like heavy bitterness, it’s recommended to choose medium or light roasted coffee beans. In addition, pouring time, water flow strength, grind size, and filter material are also key factors affecting extraction uniformity.

First is the control of brewing time. The various flavor compounds in coffee are released at inconsistent rates under the action of hot water. Especially for large-molecule substances like bitterness and astringency, they often concentrate and dissolve in the later stages of extraction. Therefore, if the brewing time is too long, not only does the concentration increase, but excessive bitter and astringent components are also likely to be released. Taking a single serving of about15–16gof coffee grounds as an example, it is recommended to keep the total brewing time within2 minutes and 30 seconds. If the actual brewing time exceeds two and a half minutes and there is a noticeable bitter or astringent taste, it’s necessary to review and adjust the relevant parameters. For instance, if the surface of the coffee bed has a lot of wet, sticky, muddy coffee grounds, it may be due to too much fine powder causing water pooling—in this case, consider adjusting to a coarser grind. If most of the coffee grounds are settled at the bottom with a flat coffee bed surface, it may be due to insufficient pouring strength, where the coffee bed isn’t fully lifted and water can only seep through slowly. It’s recommended to increase the water flow appropriately after the bloom phase, raising the water level to abouttwo-thirds of the filter cup heightto speed up the extraction flow rate.

Next, the method and stability of pouring are also crucial. Water flow that is too strong or unstable can easily lead to uneven extraction in the coffee bed, resulting in simultaneous sourness, astringency, or off-flavors. Many people have the habit of using a strong water flow to quickly agitate the coffee bed, especially in the later stages of extraction, which can easily bring out deep-seated off-flavors and astringency. To improve this, it’s recommended to use a vertical water stream, maintaining a3–4 cmdistance from the coffee bed, and pour slowly in a steady circular motion, which helps improve extraction uniformity.

Finally, the filter cup material is also an often overlooked influencing factor. For example, ceramic filter cups, due to their higher specific heat capacity, can help maintain stable water temperature during brewing if preheated sufficiently, but they may also “accidentally” increase overall extraction efficiency, raising the risk of releasing late-stage astringency. If you notice astringency in your coffee and have already ruled out grind and time issues, and you’re using a ceramic filter cup, try lowering the water temperature by2–3°C, which can help reduce the chance of over-extraction and make the coffee’s flavor more balanced.

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