Why Does Pour-Over Coffee Have a Bitter Taste? Coffee Bean Roast Level and Brewing Techniques Causing Coffee's Astringency

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Introduction

Teacher Han Huaizong once said: "The oils and colloids in coffee create a smooth texture in the mouth, while the polyphenolic compounds in coffee produce a rough astringency, like a devil's tail, running wild in the mouth and creating unpleasantness."

From a wine perspective, astringency is very important, but from a coffee perspective, astringency is not welcome. So where does coffee's astringency come from? Why does coffee produce astringency?

What is Astringency?

Astringency is the opposite of smoothness; it's the rough sensation felt when coffee enters the mouth. This texture mainly comes from dicaffeoylquinic acid, which is formed when chlorogenic acid in coffee degrades during roasting. This substance condenses with salivary proteins, creating astringent sensations on the oral epithelium. The quality of coffee raw beans determines the amount of chlorogenic acid, and under-roasting can easily cause coffee beans to have a green, astringent taste. Additionally, small amounts of tartaric acid in coffee are also sources of astringency.

What Are the Reasons for Coffee Astringency?

① Raw bean varieties contain too much chlorogenic acid

② Coffee raw beans are too fresh, leading to incomplete dehydration during roasting

③ Too many defective beans during roasting

④ Parameters and techniques when brewing coffee

Raw Bean Varieties Contain Too Much Chlorogenic Acid

Chlorogenic acid is one of the "culprits" of coffee bitterness and astringency, accounting for 6%-8% of coffee raw beans. Chlorogenic acid degrades into quinic acid through roasting. Quinic acid is a phenolic acid, non-volatile, so it cannot be smelled through the sense of smell, but it tastes bitter and has an astringent texture.

Chlorogenic acid reflects whether coffee trees are reasonably cultivated. Coffee beans with good growing environments, high cultivation altitudes, and reasonable cultivation have much lower chlorogenic acid content. This is also why Robusta coffee beans have worse flavor than Arabica coffee beans—because Robusta's chlorogenic acid content is higher than Arabica's.

Coffee Raw Beans Are Too Fresh, Leading to Incomplete Dehydration During Roasting

Fresh (new harvest) coffee raw beans have a water content of 13%. During roasting, the moisture in coffee raw beans affects heat conduction. The fresher the coffee beans, the higher the water content, and the more likely incomplete dehydration will occur during the roasting process.

Coffee beans with high water content are prone to having the surface cooked while the core remains under-roasted. Coffee beans in this condition will taste somewhat herbaceous during cupping, with a green, astringent, and sharp sensation in the mouth. Therefore, FrontStreet Coffee extends the dehydration time when roasting new harvest coffee beans to ensure even heating of both the surface and core.

Too Many Defective Beans During Roasting

Too many defective beans can easily cause uneven development or uneven dehydration during the roasting process. Even some defective beans, if present during roasting, can produce bad flavors that directly affect an entire batch of coffee beans. For example, underdeveloped coffee beans will have a roasted melon seed taste during roasting, while also making the coffee salty and astringent; contaminated fermented beans will produce a sour, rotten smell during roasting; moldy coffee beans will emit a musty smell during the roasting process.

FrontStreet Coffee sorts coffee raw beans before roasting to avoid the above situations, and also sorts the roasted coffee beans again before packaging after roasting is complete.

Parameters and Techniques When Brewing Coffee

If none of the above issues are present, then the main reasons for coffee astringency are two: under-extraction & over-extraction.

Under-extraction situations might include: coffee beans ground too coarsely, reducing extraction time; brewing water temperature too low, only extracting acidic substances from the coffee; uneven water distribution during blooming and brewing, causing some coffee powder to be under-extracted while others are over-extracted. Under-extracted coffee flavors manifest as: excessive sourness with astringent sensation.

Over-extraction situations might include: coffee beans ground too finely, increasing extraction time; brewing water temperature too high, where after the pleasant flavor substances in the coffee powder are completely released, woody fiber flavors are then released; water pouring technique too "rough," causing excessive turbulence in the powder layer leading to over-extraction. Over-extracted coffee flavors manifest as: heavy bitterness in the finish, astringency, and off-flavors.

Is the Tea Sensation in Coffee Astringency?

Tea sensation ≠ Astringency! The misunderstanding of astringency as tea sensation comes from some people thinking that bitterness and astringency in tea are normal. But actually, tea becomes astringent because the water temperature is too high or the brewing method is incorrect (of course, not excluding poor tea leaf varieties). When FrontStreet Coffee tastes Esmeralda washed Geisha green label coffee, we experience a Tieguanyin tea sensation because the lingering sweet aftertaste of the green label Geisha is very similar to Tieguanyin's aftertaste, with a sweet sensation that can linger in the mouth for a long time.

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Important Notice :

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

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