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Coffee acidity - malic, citric, acetic and more

In the world of specialty coffee, the word „acidity” is a compliment, not an accusation. To many people this sounds strange - after all, sour coffee is associated with something unpleasant. Yet for professionals acidity is the brightness, liveliness and freshness of good coffee, its most exciting feature. But acidity is not all the same: different organic acids are responsible for different impressions. One gives the taste of green apple, another a citrus flash, yet another the unpleasant, sharp sourness of old coffee. Understanding these kinds is the key to appreciating acidity as a virtue. Here is a guide to coffee acidity: why it is not a fault, which acids give which flavours and how to tell beautiful acidity from the undesirable kind.

Acidity is not a fault

Let us start by debunking a myth. In specialty coffee, acidity is a desirable feature - it means liveliness, brightness, clarity and freshness of flavour, not a sour, unpleasant aftertaste. It is the same acidity we prize in a juicy apple, citrus or wine. Good acidity makes coffee invigorating, complex and exciting, not flat and dull. It has to be distinguished from „sourness” as a fault - sharp, vinegary or under-brewed. This distinction is fundamental. Understanding that acidity is brightness, not a defect, is the starting point for the whole subject. It is the soul of fresh coffee. It is the feature connoisseurs prize most. We cover why coffee can be sour more in sour coffee.

Where the different flavours come from

Why does one coffee taste like apple and another like lemon? Because acidity is the responsibility of many different organic acids, and each has its own flavour character. Coffee contains a whole palette of them, in different proportions depending on origin, variety, processing and degree of roast. It is these specific acids, not some single general „sourness”, that create the impression of apple, citrus or grape. Getting to know the main acids lets you understand and name what you sense. It is like breaking acidity down into its component parts. Understanding that different acids give different flavours opens the door to precision in description. It is chemistry turned into flavour. It is the key to understanding the brightness of coffee.

Malic acid

The first important acid is malic acid. As the name suggests, it gives the taste of green apple - crisp, juicy, slightly tart. It is also notes of pear and stone fruit. Malic acid is prized for a pleasant, fruity freshness that is associated with a crunchy apple. It is often found in coffees of a clean, fruity profile, for example from some regions of Central America or Ethiopia. It gives coffee juiciness and an appetising crispness. Understanding that malic acid is the taste of green apple lets you recognise it in the cup. It is the fruity flash of coffee. It is an acidity that is easy to like.

Citric acid

The second acid is citric acid. It gives the taste of citrus: lemon, lime, orange - bright, sharp, shining. It is one of the most recognisable and well-liked acidities in coffee, associated with morning orange juice. Citric acid adds liveliness and clarity to coffee, making it refreshing. It is often found in coffees from high altitudes, for example from Latin America or East Africa. It is a bright and exciting acidity. Understanding that citric acid is the taste of citrus lets you name it. It is the citrus brightness of the cup. It is one of the most beautiful acidities of coffee.

A table: kinds of acidity

Let us gather the main acids in one place:

The table shows that not every acidity is the same: some acids give a beautiful brightness, others (in excess) are a fault. The key is recognising which flavour you sense.

Phosphoric acid

The third acid is phosphoric acid. It is an inorganic acid that gives an impression of sparkling, intense, sweet-tart acidity - bright and almost effervescent. It is associated with the most lively, shining coffees. Phosphoric acid is often linked with coffees from Kenya, famous for an exceptionally intense, almost blackcurrant and grapefruit acidity. It is the one behind that characteristic, electrifying brightness. It gives coffee an energy and intensity that is hard to mistake. Understanding that phosphoric acid is a sparkling, intense acidity lets you appreciate this type. It is the electric flash in coffee. It is an acidity that delights connoisseurs.

Acetic acid - good and bad

The fourth acid is acetic acid, and here the subtlety begins. In small amounts acetic acid gives a pleasant, winey, almost fruity-fermented note that adds complexity to coffee - associated with wine or balsamic vinegar. But in excess it becomes a fault: a sharp, stinging taste of vinegar, usually the result of over-fermentation of the beans during processing. It is a good example that the same acid can be a virtue or a defect depending on the amount. The increasingly popular fermented coffees balance on this edge. Understanding that acetic acid can be a winey note or a vinegary fault teaches vigilance. It is acidity on a knife’s edge. It is the line between complexity and defect.

Quinic acid - the bad sourness

The fifth acid is quinic acid - and it is the one behind the unpleasant „sourness”. It forms when other coffee acids break down: during too heavy a roast, in old, stale coffee or with a held-over brew. Quinic acid gives a sharp, bitter-sour, astringent note - that unpleasant sourness associated with old coffee from a petrol station. It is not a beautiful brightness, but a defect. That is why dark roasts and old coffee lose their noble acidity and gain this bad one. Understanding that quinic acid is the bad sourness of old and over-roasted coffee lets you tell it apart from beautiful acidity. It is the acidity you avoid. It is a sign that the coffee is old or over-roasted.

Origin, processing and roast

Where does coffee draw such and such an acidity from? Three factors decide. The first is origin and altitude: coffees from high altitudes (like Kenya, Ethiopia or the mountain regions of Latin America) have a higher, more expressive acidity, because the cold slows the ripening of the cherries and concentrates the acids. The lowlands give gentler, less acidic coffees. The second is processing: washed coffees usually have a clean, bright, expressive acidity, while natural or fermented ones have a different, more fruity-winey one. The third is the roast: a light one preserves the noble acids, a dark one destroys them. These three levers shape the acidic character of every coffee. Understanding that origin, processing and roast control acidity lets you predict the flavour. It is geography and craft in the acids. It is the reason Kenyan coffee sparkles and Brazilian is gentle.

How to sense it and use it

How to use this knowledge in practice? When tasting coffee, instead of just saying „sour”, try to name the type: is it apple (malic), citrus (citric), a sparkling flash (phosphoric), a winey note (acetic), or a sharp, unpleasant sourness (quinic)? This exercise sharpens the palate enormously. Remember that a light roast preserves the beautiful acids, and a dark one destroys them, giving quinic acid. Fresh coffee has brightness, old coffee has the bad sourness. Note what acidity you sense, to build flavour memory. Understanding how to recognise the types of acidity turns a general impression into a precise description. It is a higher level of tasting. We cover describing impressions more in the coffee flavour profile.

The essentials in brief

Let us gather it up. In specialty coffee, acidity is a virtue - brightness, liveliness and freshness, not a fault. Different organic acids are responsible for different impressions. Malic acid gives the taste of green apple, citric of citrus, and phosphoric a sparkling, intense acidity (as in coffees from Kenya). Acetic acid in a small amount gives a pleasant, winey note, but in excess becomes a vinegary fault from over-fermentation. Quinic acid is that bad, sharp sourness, forming with too heavy a roast and in old coffee. A light roast and freshness preserve the beautiful acids, a dark roast and age destroy them. By naming the type of acidity, you will sharpen your palate. Now you know that coffee acidity has many faces.

Note every coffee in GustoNote - including the kind of acidity you sense: malic, citric or sparkling. In time you will learn to recognise the acids and tell a beautiful brightness from a bad sourness yourself.