Introduction:If you experience a gritty, rough, or astringent mouthfeel when drinking pour over coffee, it could be caused by a combination of factors. This article delves into the sources of coffee astringency—including bean ripeness, roasting techniques, defective beans, and brewing parameters—to help you distinguish between good and bad astringency, master brewing methods to reduce astringency, and make every cup of pour over smoother and more palatable.
Pour over coffee can occasionally produce an unpleasant gritty sensation, often described as “astringency.” Whether it’s the lack of smoothness upon entry or the roughness on the tongue afterward, it can detract from the overall drinking experience. So why does astringency occur in pour over coffee? How is it formed? And how can we improve it by adjusting our green bean selection and brewing techniques?
In fact, astringency in coffee isn’t unique—similar sensations can also be found in the tannins in red wine or the catechins in tea. In coffee, astringency is mostly related to chlorogenic acids, as well as the processing, roasting, and extraction processes. Chlorogenic acid is a natural antioxidant found in plants, and its content can vary depending on the growing conditions and processing methods of the green beans.
Coffee astringency can generally be attributed to the following common causes: First, harvesting coffee cherries before they are fully ripe can result in underdeveloped internal compounds, affecting subsequent flavor expression; second, incomplete dehydration or uneven heating during roasting may lead to noticeable astringency in the final coffee beans; third, the presence of defective beans such as insect-damaged or underripe beans is also a common cause of astringency; finally, brewing parameters and techniques such as water temperature, grind size, water flow control, and pouring method can also greatly influence whether astringency occurs.
It’s worth mentioning that not all astringency is negative. A moderate level of astringency can sometimes add complexity and aftertaste to the coffee, especially when tasting new-season beans—slight astringency can even be an indicator of the beans’ freshness. However, this kind of positive astringency usually diminishes over time, typically fading after three to four months of resting and transforming into a rounder mouthfeel.
So, what situations can clearly lead to unpleasant astringency in pour over coffee? When we confirm that the roast quality is sound, the issue usually lies in the presence of defective beans or improper brewing parameters and techniques.
Before you start brewing, there’s one thing you absolutely must not overlook:Be sure to remove defective beans. This is crucial—before grinding, carefully inspect and pick out any obvious insect-damaged, moldy, or underripe beans to prevent them from releasing undesirable flavors during extraction.
Coffee astringency mainly stems from two major extraction issues: over-extraction and uneven extraction. Generally, only about 30% of a coffee bean is water-soluble, and of that, only 20% contributes pleasant flavors—the remaining 10% may contain off-flavors. If over-extracted, these undesirable components are released, leading to a numbing, astringent, or even bitter sensation on the tongue.
Over-extractioncommonly manifests as an overly bitter aftertaste or the emergence of off-flavors, usually due to high water temperature, too fine a grind, excessive stirring during pouring, or leaving the coffee to drip for too long in the filter. Even brief pauses can lead to over-soaking, causing the coffee to release too many unwanted substances.
Uneven extractioncan result in some coffee grounds being over-extracted while others are under-extracted, creating an imbalanced flavor profile. Common causes include uneven blooming, inconsistent water stream thickness, irregular pouring circles, or unstable pouring pressure. As a result, some areas of coffee grounds may release too many compounds, while others remain under-extracted, leading to an overall messy taste with a mix of sour and bitter or astringent notes.
To avoid these issues, it’s recommended to maintain a stable water flow and even pouring path, controlling the speed and range of each pour to ensure all coffee grounds absorb water and release flavors uniformly. Additionally, using a moderate grind size and appropriate water temperature (typically recommended between 90°C and 94°C) can also effectively reduce the risk of over-extraction.
Beyond technical aspects, we often confuse “astringency,” “tea-like sensation,” and “dryness.” While all three are part of mouthfeel, they are fundamentally different.Astringency is a tactile sensation, similar to a rough or uneven feeling on the surface of the mouth, like drinking a liquid with fine sand in it. This sensation is generally considered a negative factor in cupping.
In contrast,a tea-like sensation refers to a lingering aftertaste or slight bitterness similar to tea, but without uncomfortable roughness—for example, some high-quality Geisha may have a green-tea-like fresh mild bitterness, yet still feel smooth. Meanwhile,dryness is often related to throat discomfort, commonly occurring with overly fresh beans or uneven roasting dehydration, making the throat feel dry or tight. Such cases often require letting the beans rest for a few days before trying again.
In summary, if you notice significant astringency in your pour over coffee, first determine whether it leans more toward bitter astringency or sour astringency. If the bitter astringency is stronger, consider adjusting the brew time—avoid over-extending extraction or shortening the final pours. If sour astringency dominates, check whether your pouring technique is even and confirm whether under-extraction is caused by too coarse a grind or too low a water temperature. By gradually adjusting these variables, you’ll be able to find the balance that best suits your taste and enjoy a smoother, more layered pour over coffee experience.
The above content is compiled by CoffeeHunters, a coffee news website.
