How to Reduce the Dry Mouth Effect from the Drink
There is a common myth that coffee causes dryness in the mouth because the caffeine it contains dehydrates the body. However, in moderate amounts, caffeine does not affect the body's water-salt balance and may even promote fluid intake. Nevertheless, many coffee enthusiasts still experience dryness in the mouth, even after a cup of decaffeinated coffee.
In this article, we explain why coffee actually causes a dry mouth sensation and how you can mitigate this effect. Our explanation is based on material from Barista Hustle.
How to Accurately Describe the Dry Mouth Sensation After Coffee
The dryness in the mouth after drinking coffee is more accurately described as astringency. This sensation resembles the feeling of sand on the tongue and is similar to the astringent effect of strong black tea or an unripe banana.
Dryness is a characteristic of many products. For example, dry white wine, although it contains fewer astringent substances than coffee or tea, evokes similar sensations due to its low residual sweetness and high acidity.
White wine is not referred to as astringent because the astringent effect it causes is short-lived.
Why Coffee is Astringent
Astringency in products is generally due to a large group of polyphenols known as tannins. However, the molecules responsible for astringency in coffee often differ structurally from traditional tannins. To categorize them under the broader group of phenolic compounds would be inaccurate, as this group includes many molecules that do not cause astringency. Therefore, the astringent substances in coffee are simply called "pseudo-tannins" due to their similar effect.
The term "tannins" originates from the leather industry, where plant components were used in the tanning of animal hides. Oak bark was the primary source of tannins, and in ancient Celtic languages, oak was referred to as "tann"
Tannins are a class of complex chemical compounds that are found in many plants, including grapes, trees, and other fruits, leaves, and legumes.
They are a type of polyphenol, and are known for their bitter and astringent taste. Tannins are large molecules that can bind to other molecules, such as proteins, cellulose, and minerals, to form insoluble substances that are resistant to decomposition.
Tannins and pseudo-tannins function similarly: when we drink coffee, these chemical compounds react with the proteins in our saliva, forming sediment particles on the tongue. This reaction causes the proteins to lose their lubricating properties, leading to a dry and sandy sensation in the mouth. Due to this similar effect, tannins and pseudo-tannins are often collectively referred to as "tannins" in the coffee industry and scientific literature. These are large molecules that bind with proteins to form sediment.
The astringency of coffee primarily depends on the level of extraction during brewing.
How Extraction Influences Tannin Content
Controlling extraction is crucial for limiting the tannin content in coffee. The general rule is simple: the higher the extraction, the more astringent the drink will be. This is because many tannins are poorly soluble in water, meaning they influence the coffee's taste only at high levels of extraction. The largest tannins are extracted into the cup only when the coffee reaches its maximum possible extraction level—around 30%. Therefore, compared to an under-extracted beverage, an over-extracted one will contain more tannins, resulting in a more pronounced astringency.
During channeling, coffee can become astringent even if the overall extraction levels are within the normal range.
During the brewing process, channeling can cause coffee to become astringent even if the overall extraction indicators seem normal. In cases of channeling, the water flow around the channels can be so intense that local extraction reaches 30%, even if the overall drink remains under-extracted. As a result, more tannins from the over-extracted areas will end up in the cup, while sugars from the rest of the coffee dissolve to a lesser extent. This leads to a beverage where astringency predominates.
How to Influence the Perception of Astringency
Besides extraction, several other factors do not directly affect tannin content but do influence the perception and taste of the cup:
1. Acidity and Salinity Levels: The higher they are, the more astringent the coffee feels.
2. Sweetness Level: The fewer sugars in the coffee, the more pronounced the astringency.
3. Temperature: The lower the temperature, the stronger the astringency. This is why sugar is added to iced coffee for flavor balance; the cold drink becomes too astringent, and sweetness helps to balance the perception.
4. Fat and Oil Content: The more these substances are extracted, the less pronounced the tannin effect. For instance, during espresso preparation, a significant portion of coffee oils is extracted, resulting in a beverage with less pronounced astringency.
Thus, the perception of astringency in coffee can also be reduced by adding milk to the drink. The sugars and fats in milk counteract the astringent effect of coffee.
Summary
The sensation of dryness in the mouth after drinking coffee is referred to as astringency, caused by polyphenols—tannins and pseudo-tannins—found in coffee beans. In the coffee industry, these substances are collectively called "tannins" due to their similar astringent effect, although their molecular structures differ.
The tannin content in a cup of coffee depends on the level of extraction. The higher the extraction, the more astringent substances are present, and the more pronounced the astringency becomes. Channeling during coffee preparation also leads to increased tannin dissolution and a stronger astringent effect.
Other factors, such as the acidity, sugar content, fat content, and temperature of the beverage, also influence the perception of astringency in coffee.