Is it Normal for Coffee to Taste Astringent/Bitter? How to Solve Over-Extraction in Pour-Over Coffee?

For most people, it's difficult to reach a consensus on what flavors a cup of coffee might have. However, when it comes to noticeable astringency or astringent sensations in coffee, nearly everyone can detect it immediately after taking the first sip.

FrontStreet Coffee's backend frequently receives messages from readers, with many asking how to avoid brewing coffee with astringent flavors. Just last week, for instance, one reader mentioned that despite noticing nothing unusual during the brewing process and keeping all parameters within the extraction plan, the coffee still had an uncomfortable sensation. When swallowing, their throat and tongue experienced a sand-like roughness that lingered for a long time. They suspected this was caused by excessive astringency and wanted to identify where things went wrong.

In FrontStreet Coffee's view, to solve the uncomfortable "astringency" in coffee, we must first understand this sensation and identify its release patterns, then we can fundamentally avoid such problems from occurring.

What Exactly is Astringency?

So-called astringency is actually a "grabbing" constriction sensation produced in the mouth and on the tongue, or a very rough wrinkling sensation. In other words, astringency means lack of smoothness, so it's a tactile sensation rather than a taste.

Although it differs from flavors like sour, sweet, and bitter, as a tactile sensation that most people cannot accept, once we perceive the presence of "astringency," even if the food's aroma is rich, our minds typically focus first on this negative impression. Like when FrontStreet Coffee eats an unripe banana, although the fruit aroma is perceived, the roughness that forms on the dental membrane afterward remains uncomfortable.

Where Does Astringency in Coffee Come From?

In daily life, tea, red wine, and coffee all exhibit astringent tastes, but their sources differ. The astringency in tea comes from tea polyphenols, while red wine's astringency comes from tannic acid found in grape skins and seeds. The astringency in our coffee comes from dicaffeoylquinic acid, which is formed when chlorogenic acid from green beans degrades during roasting, along with substances like tartaric acid and tannic acid.

If the coffee you drink has obvious sand-grain-like roughness, mouth obstruction, throat catching, dryness, or other astringent-tasting sensations, it's highly likely that these substances have dissolved excessively or occupy too large a proportion in the coffee.

Strictly speaking, there are many reasons why coffee might develop astringency, including insufficient fruit ripeness during harvest, high defect rates in green beans, overly rough post-processing, improper transportation and storage, insufficient development during roasting, and uneven extraction—all potential "culprits" that can cause astringent sensations in coffee.

However, as consumers, as long as you purchase from trustworthy brands, you basically won't encounter coffee with astringency caused by green beans or roasting issues. This is because these products have undergone multiple layers of quality control by origin farmers, green bean suppliers, roasters, baristas, and other professionals before officially hitting the shelves, ensuring their quality is up to standard. So when you've confirmed there are no issues with your purchased product but frequently experience astringency in brewed coffee, you might want to look for causes in the following brewing details.

Which Situations Most Easily Lead to Astringency in Coffee?

1. Brewing Time Too Long

Many people know that various substances in coffee release at different rates under the scouring of hot water. Large molecular substances mainly contributing to bitterness and astringency typically dissolve concentratedly in the later stages. Therefore, astringency in coffee is often accompanied by unpleasant bitter notes. From an extraction logic perspective, the longer coffee is brewed, the stronger the flavor becomes, and the more likely it is to release bitter and astringent tastes in the later stages.

Therefore, to achieve proper extraction of coffee, you need to control the brewing time. Taking a single serving of 15-16g of coffee grounds as an example, FrontStreet Coffee suggests not exceeding 2 minutes and 30 seconds. When your actual brewing time exceeds two and a half minutes and you indeed taste bitterness and astringency, then to improve the coffee's flavor, you must adjust parameters according to the actual situation.

For example, if there's a large amount of wet, muddy powder on the surface of the coffee bed after brewing, it indicates that too many fine particles have caused water pooling, and you need to adjust to a coarser grind size;

If the coffee grounds are mostly concentrated at the bottom and look very flat, it's likely because the water pouring force was too small, causing the coffee bed to not lift properly. Water could only slowly seep down through the thick barrier layer, thereby prolonging the brewing time. The solution is to appropriately increase the water flow rate after the bloom period, trying to raise the water level to about 2/3 of the filter cup's height.

2. Water Flow Scouring Force Too Strong

According to FrontStreet Coffee's observation, there are two main situations where water pouring issues cause astringency: the first is unstable water flow leading to uneven particle extraction, making the coffee both sour and astringent; the second often comes from friends who habitually use large water flows to stir the coffee powder layer, which easily washes out miscellaneous flavors and astringency in the later extraction stages.

Unlike other parameters, water pouring belongs to practical techniques that require constant practice. To achieve even brewing, FrontStreet Coffee suggests using a vertical water column, maintaining a height of 3-4cm from the powder layer, and slowly pouring in circular motions.

3. Filter Cup's Extraction Efficiency Too High

For many beginners, the material of the filter cup is one of the most overlooked causes of over-extraction. For example, ceramic filter cups have the characteristic of high specific heat capacity. Preheating can ensure good heat retention throughout the pouring process, but it also "quietly" increases the extraction efficiency of coffee, thereby increasing the probability of astringency release in the later stages.

Therefore, when we taste astringency in coffee, and the filter cup being used is made of ceramic material, and we've already ruled out the first two situations, then we might want to start with temperature, try reducing the brewing water temperature by 2-3°C to slow down the risk of over-extraction.

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