What causes astringency in pour-over coffee?

Astringency in pour-over coffee comes mainly from chlorogenic acid, the same family of compounds behind the drying feel of red wine tannins and tea catechins. It shows up when cherries are picked underripe, when roasting dehydrates unevenly, when defective beans slip into the batch, or when brewing parameters push extraction too far.

Two brewing faults dominate: over-extraction and uneven extraction, which leave a sandy, rough texture after coffee. Astringency is not always a defect, though, so the useful step is telling it apart from a tea-like sensation and true dryness, then adjusting grind, water temperature and pour pattern before changing the beans.

When drinking coffee, you may occasionally encounter an unpleasant experience that isn't smooth enough and has a slightly sandy texture—this is what we commonly call astringency. Where does astringency actually come from? It may originate from the cultivation and processing of green beans, and may also be closely related to roasting, the mixing in of defective beans, and brewing parameters and techniques. This article will start from the material basis of astringency, sort out the difference between positive and negative astringency, analyze the two major brewing causes of over-extraction and uneven extraction, and also clarify the differences among astringency, tea-like sensation, and dryness, finally giving practical adjustment ideas. The article also retains related product and recommendation information from Front Street Coffee, making it convenient for coffee lovers to refer to in daily brewing.

Sometimes when you take a sip of coffee, you feel it isn't smooth enough, and an uncomfortable sandy texture appears in your mouth—this is what we usually call "astringency." So how exactly is astringency produced? And how can it be avoided as much as possible during brewing?

| Astringency Astrigent

In fact, astringency doesn't only appear in coffee. Tannic acid in red wine and catechins in tea leaves both bring similar sensations, while in coffee it is mainly related to chlorogenic acid. Chlorogenic acid, like caffeine, is a substance produced by plants in response to changes in the external environment, so the level of chlorogenic acid can also reflect, to a certain extent, the growing condition of green beans.

Astringency usually appears in the following situations:

1. The coffee fruit is harvested and processed before it is fully ripe;

2. During roasting, dehydration is incomplete, or heating is uneven;

3. Defective beans are mixed in, such as insect-damaged beans and immature beans;

4. Brewing parameter settings and operating techniques.

However, astringency cannot be regarded entirely as negative. We also distinguish between good astringency and bad astringency.

Negative astringency directly exposes defects in coffee quality. This type of astringency, formed during cultivation or processing, is often difficult to reverse. For example, leaves are mixed in when picking coffee cherries, or the fruit is picked before it is ripe enough; another example is improper operation during roasting and uneven temperature distribution, which are also sources of astringency.

But even coffee beans that have been carefully picked and sorted will still carry a certain degree of astringency within a few months after processing is completed. An appropriate amount of astringency can enrich the layers of coffee and make the flavor linger longer in the mouth. If bitterness can return sweetness and astringency can promote salivation, then high-quality bitterness and astringency are sometimes instead a manifestation of coffee quality.

From past experience, the earliest newly arrived seasonal beans each year often show a certain degree of astringency in cupping, and this precisely indicates that the beans are fresh enough. These freshly processed coffee beans usually need 3~4 months before the astringency completely fades, so when tasting new-season coffee beans, astringency can instead serve as evidence that the green beans are fresh.

What situations can make brewed coffee carry astringency?

On the premise that there are no problems with roasting, it may be that defective beans were mixed in, or there may be problems with brewing parameters and techniques.

So, before brewing you must sort out defective beans! you must sort out defective beans! you must sort out defective beans!

The main reasons astringency appears lie in over-extraction, and uneven extraction leading to part over-extraction and part under-extraction these two situations.

Among the total substances in coffee beans, water-soluble substances account for only 30%, while the remaining 70% is composed of insoluble fiber and carbohydrates. Of these, 20% of the water-soluble substances can bring good flavor, while the other 10% of soluble substances contain terrible tastes that people avoid. Once extraction is excessive, those unacceptable unpleasant flavors are released and become a numbing bitterness on the tongue.

| Over-extraction

Over-extraction mainly manifests as a heavier bitter taste in the tail end, with impurities being brought out and becoming bitter. A high water temperature (or a heat source continuously heating the water), grinding too fine or too many ultra-fine particles, and stirring too frequently can all cause over-extraction. Sometimes we may also get over-extraction during just the brief few seconds of waiting for the water in the dripper to drip down.

| Uneven extraction

Uneven extraction mainly causes flavor imbalance, with excessive acidity bringing a sour and astringent sensation. Uneven water supply during blooming and brewing will cause part of the coffee grounds to be under-extracted and part to be over-extracted.

Uneven water supply, that is, the stream of water alternating between thin and thick, the circling not being round, and the pouring not being symmetrical, results in water overflowing where more is poured and flowing away through the filter paper; where less is poured, the coffee grounds cannot be fully wetted, and the blooming effect is greatly reduced. Ultimately, during the later-stage pouring and extraction, part is over-extracted and part is under-extracted, the flavor is messy, and astringency is easily produced.

[Tips]

How to distinguish astringency, tea-like sensation, and dryness?

Astringency is a tactile sensation or pain sensation. The author believes it is a non-smooth tactile sensation, like something covered in dust, a sandy feeling. Astringency and smoothness are the two major mouthfeels of coffee. In cupping, astringency is penalized, while smoothness is rewarded.

Astringency is not equal to a tea-like sensation. Mistaking astringency for a tea-like sensation is a misunderstanding, because some people think tea is also bitter and astringent, but some green teas do not taste bitter or astringent when drunk and have a stronger fresh sweet sensation. As long as the brewing method and water temperature are correct, no bitterness or astringency can be felt at all when drinking, and it is quite smooth. For example, we often taste green tea flavors in Front Street's Geisha. With correct extraction, there will be a tea-like sensation but no astringency; similarly, in Front Street's Sidamo we taste black tea, and in Costa Rica Black Honey we taste oolong tea flavors. This tea-like sensation is slightly bitter, with a long lingering aftertaste in the mouth, and sweetness gradually overcomes bitterness, finally ending with sweetness.

Dryness generally refers to the discomfort that appears after coffee enters the mouth, making the throat uncomfortable and causing the throat to feel dry. It is usually called "dryness." There is a similar expression in tea drinking, also called "throat-locking." Dryness is mostly because the beans are too fresh, or because dehydration during roasting is uneven.

If astringency appears during everyday brewing, you may first carefully feel whether it is bitter-astringent or sour-astringent. If it is bitter-astringent, then too many substances may have been extracted, and you can try adjusting the brewing parameters or removing the tail end; if it is sour-astringent, then the extraction may be uneven, and you need to check whether there is anything in the brewing technique that can be improved.

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