Introduction:Have you ever brewed coffee at home only to find it tasting off but can’t quite put your finger on why? In many cases, the issue might stem from “under-extraction” or “over-extraction.” This article will take an in-depth look at the definitions of these two common extraction issues, the reference ranges and limitations of the Golden Cup standard, and help you accurately diagnose your coffee’s problems through real flavor characteristics. Finally, we’ll provide practical adjustment strategies using grind size as the variable, so you can brew better-tasting pour over coffee.

When brewing coffee at home, it’s common to end up with a cup that’s either too weak or too bitter and astringent, sometimes even with strange off-flavors, yet you’re not sure what went wrong. In fact, these common issues mostly arise from improper extraction — namely “under-extraction” or “over-extraction.” Mastering the characteristics and adjustment methods of these two is key to improving your brewing skills as a coffee enthusiast.

Extraction refers to the process of dissolving the flavor compounds in coffee grounds using water. According to Golden Cup extraction theory, the ideal extraction yield should fall between18% and 22%. Below 18% is under-extraction, and above 22% is over-extraction. However, it’s important to note that the Golden Cup criteria are just a reference, not an absolute standard. Factors such as coffee quality, variety, and roast level can all affect the final flavor profile.

Therefore, rather than obsessively pursuing numerical perfection, it’s more important to judge the extraction status through taste. When you find that your brewed coffee doesn’t taste quite right, you can infer whether it’s under-extracted or over-extracted based on its flavor profile, then further adjust parameters to bring the coffee’s flavors back into balance.

Under-extraction, as the name suggests, means that only a small portion of the flavor compounds in the coffee have been successfully extracted. Generally speaking, about 30% of the soluble substances in coffee beans are extractable, but during under-extraction, only around 10% to 15% are typically dissolved, preventing many desirable flavors from being released.

Under-extracted coffee often exhibits the following three main flavor characteristics: First isa lack of flavor intensity, where insufficient aroma and taste result in muted scents and thin flavors; second isa watery mouthfeel, where insufficient extraction leads to a diluted, thin-bodied taste even if the brew ratio is normal; and third isprominent sourness, astringency, or saltiness, which occurs because acidic molecules are smaller and dissolve faster. If the extraction time is too short, acids are released first, while sweetness and bitterness haven’t had enough time to fully develop, resulting in an overly sharp acidity, possibly accompanied by unpleasant astringency or saltiness.

These issues may stem from using a grind that’s too coarse, water that’s too cool, a brew time that’s too short, insufficient water volume, or inadequate agitation. If your coffee tastes bland or has clearly unpleasant notes, under-extraction might be the first thing to suspect.

Conversely, over-extraction is the result of dissolving too many substances from the coffee — especially undesirable large molecular compounds. These substances often carry strong bitterness, astringency, or even unwanted woody, cardboard, or straw-like off-flavors.

Common problems with over-extracted coffee includeintense bitterness,a dry, puckering mouthfeel, and the emergence of unwantedwoody or vegetal off-flavors. These negative flavors are often easy to identify because they significantly overshadow the coffee’s intended sweetness and balance.

The causes of over-extraction are usually related to excessively high extraction efficiency, such as using a grind that’s too fine, water that’s too hot, a brew time that’s too long, or overly vigorous water flow and agitation. Especially when the brew time drags on too long, it becomes easy to extract undesirable compounds that should have remained in the coffee grounds, leading to an imbalanced overall flavor.

So, if you find your coffee suffering from any of the above issues, how can you adjust? The key lies in changing the extraction efficiency, and the most practical and easy-to-control method is to adjust thegrind sizeto control the extraction rate. It’s recommended to keep water temperature, brew ratio, brew time, and water volume constant, and only vary the grind coarseness to observe flavor changes.

For example, if you’re brewing a light roast coffee bean, you can usewater at 91–93°C, abrew ratio of 1:15, and abrew time of about two minutes. If it tastes overly thin, overly sour, or watery, try grinding finer to increase extraction efficiency; conversely, if the coffee shows obvious bitterness, astringency, or off-flavors, grind coarser to reduce the risk of over-extraction.

This adjustment method is simple and effective, helping you quickly find the right extraction parameters for your current coffee beans. Of course, besides grind size, factors like fines content, filter design, and water flow stability can also affect extraction results. For those who want to dive deeper into these advanced variables, it’s recommended to explore more professional resources to enhance your overall brewing skills.

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