How is coffee processed to reduce astringency in the cup?

Astringency is a tactile sensation, not a taste: tongue numbness and a dry mouth caused by friction between coffee liquid and the oral cavity. Polyphenolic compounds in coffee beans, especially chlorogenic acid, are released in excess, bind with salivary proteins, and weaken lubrication. It often appears alongside acidity or bitterness as sour-astringency or bitter-astringency.

Most astringent compounds are large molecules that dissolve slowly, so clear negative astringency usually signals under-extraction or over-extraction. Because chlorogenic acid also contributes sourness and bitterness, adjusting extraction efficiency is the practical route to improvement, and knowing how is coffee processed helps separate astringency from green beans themselves from astringency caused by brewing.

When drinking coffee, a numbing sensation on the tongue and a dry mouth—this rough tactile feeling is astringency. Astringency is not a taste, but a tactile feedback caused by friction between the coffee liquid and the oral cavity. Its root lies in the polyphenolic compounds in coffee beans—especially chlorogenic acid—being released in excess, which bind with salivary proteins and weaken lubrication. Astringency often interweaves with acidity and bitterness, forming sour-astringency or bitter-astringency. This article will start from the causes of astringency, explain its relationship with extraction states, analyze which astringency is a quality expression, as well as the astringency that green beans themselves may bring, and provide specific ideas for improvement by adjusting extraction efficiency.

Words like full-bodied and light describe the sense of weight that coffee liquid occupies in the mouth. Astringency is different—it refers to the rough tactile sensation that coffee liquid brings to the oral cavity: tongue numbness, dryness, or a lack of smoothness. These negative sensations can all be categorized as astringency.

The reason coffee becomes astringent is rooted in the excessive release of polyphenolic compounds from coffee beans. Chlorogenic acid, tannic acid, and other substances are the main sources of astringency, with chlorogenic acid playing the most prominent role. Once they come into contact with saliva, they react with the proteins in the salivary film, thereby reducing saliva's original lubricating ability.

The role of lubrication is originally to reduce friction. When the lubricity of saliva covering the tongue surface is weakened, the friction on the tongue surface increases accordingly. When coffee liquid enters the mouth, it produces more friction with the tongue surface, which we then perceive—this is astringency.

Chlorogenic acid is not only related to astringency; it is also one of the sources of sourness and bitterness. Therefore, astringency often does not appear alone—it tends to appear together with bitterness or sourness, becoming sour-astringency or bitter-astringency.

Since most substances that cause astringency are large molecules with relatively slow dissolution rates, when a cup of coffee shows obvious negative astringency, it usually indicates that it is in an under-extracted or over-extracted state. In most cases, astringency is caused by over-extraction—like green tea steeped too long, astringent to the point of being unpleasant. In this case, the problem can be solved by reducing extraction efficiency.

Of course, astringency is not always a bad thing.

Quality astringency does not overpower the coffee's flavors and taste. It gently emerges after the flavors have been expressed, allowing one to notice its presence without interfering with other sensations—thus it can be considered a more layered expression. However, this type of astringency is usually quite rare.

Besides brewing factors, astringency may also come from the coffee beans themselves.

In addition to brewing errors causing excessive release of polyphenolic compounds, the coffee beans themselves may also contain too many of these substances, giving the extracted coffee an inherent astringency.

There are two situations that cause coffee beans themselves to have excessive polyphenolic compounds. One is picking coffee cherries before they are fully ripe. Beans processed from such cherries, due to incomplete development and insufficient accumulation of other substances, make the astringent components appear disproportionately dominant.

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