What Is Coffee Acidity?

Coffee acidity refers to the bright, crisp, and sometimes fruity qualities that create a lively sensation on the palate. It is a pleasant snap or crispness and it has nothing to do with the pH level of the coffee. In other words, a coffee can taste bright and vibrant without being harsh or sour.

When coffee professionals describe a brew as “bright,” “crisp,” or “lively,” they are referring to acidity. In the world of specialty coffee, acidity is one of the most celebrated qualities in the cup. Furthermore, it is one of the primary attributes that Q-graders, professional tasters certified by the Coffee Quality Institute, use to score coffee quality alongside body, sweetness, and aftertaste.

Why Does Acidity Matter?

Think of acidity as the sparkle in your coffee. Without it, the cup can taste flat, heavy, and lifeless. As a result, acidity is one of the key distinctions between specialty coffee and commodity coffee.

In addition to adding brightness, acidity interacts with sweetness and body to create a more complex sensory experience. When properly balanced, it enhances perceived sweetness, much like a squeeze of lemon brightens the flavour of fresh berries. On the other hand, when acidity is out of balance, it tips into unpleasant sourness. The goal is always harmony.

The Key Acids in Coffee Explained

Coffee contains dozens of organic compounds, but a handful of acids do most of the flavour work. Food scientist Joseph A. Rivera explored these in depth in Roast Magazine, and the chemistry is worth understanding.

Chlorogenic Acids (CGA)

Chlorogenic acids are the most abundant acids in green coffee beans, accounting for six to seven percent of arabica beans by dry weight. They are significant contributors to the body and perceived brightness of the cup. Because they are heat-sensitive, they degrade during roasting into quinic acid and caffeic acid and as a result, darker roasts contain higher levels of these breakdown products, which can impart bitterness and astringency. Furthermore, chlorogenic acids are powerful antioxidants, which is one reason coffee is associated with health benefits.

Citric Acid

Citric acid gives coffee its lemon and orange-like brightness, and it is one of the major acids contributing to cup profile. It is not produced during roasting, instead, heat slowly breaks it down. As a result, lighter roasts retain more citric acid and tend to taste brighter. Beans from Kenya, Ethiopia, and other East African origins are particularly known for their citric acid content, which produces a vivid, fruit-forward character in the cup.

Malic Acid

Malic acid is commonly known as “apple acid” because it produces an apple-like crispness on the palate. It is one of the major acids found in green coffee and decreases upon roasting, beginning to decompose at around 190°C. In specialty coffee, malic acid contributes a clean, rounded brightness that differs from the sharper quality of citric acid, it tends to register on the sides of the tongue rather than at the front.

Acetic Acid

Acetic acid is the same acid found in vinegar. In high concentrations it is undesirable, but in trace amounts it plays an important role in coffee aroma and perceived brightness. Because it is highly volatile, it escapes from the cup during brewing and reaches the nose before the lips, in this way, it contributes significantly to the aromatic complexity of the coffee. It is found in greater quantities in washed coffees due to the fermentation process, and in these trace amounts it contributes a desirable cleanliness to the cup.

Phosphoric Acid

Unlike the other acids in this list, phosphoric acid is an inorganic acid. Research by Joseph Rivera at the Coffee Quality Institute found higher concentrations of phosphoric acid in specific East African coffees, including Kenya AA and SL28 varieties, compared to Colombian Supremo. In addition, experiments where phosphoric acid was added to other coffee origin brews significantly altered their acid profiles to levels almost identical to Kenyan coffees. It is believed to impart brightness and enhance sweetness rather than contributing sourness.

Quinic Acid

Quinic acid forms as chlorogenic acids break down during roasting. It adds astringency and body to the cup, and it is found at higher levels in darker roasts. On one hand, a moderate presence of quinic acid contributes mouthfeel and structure. On the other hand, excessive quinic acid, which develops when brewed coffee sits on a heating element for an extended period, produces a harsh, overly bitter taste. This is why freshly brewed coffee always tastes better than coffee that has been held on heat for hours.

Frequently Asked Questions

What does acidity mean in coffee?

Acidity in coffee refers to the bright, crisp, and lively quality that makes a cup feel alive on the palate. It is not sourness. In specialty coffee, acidity is a desirable characteristic that adds complexity, depth, and vibrancy to the cup.

What acids are found in coffee?

The key acids in coffee include chlorogenic acids, citric acid, malic acid, acetic acid, phosphoric acid, and quinic acid. Each contributes differently to flavour, aroma, and mouthfeel. Chlorogenic acids are the most abundant in green coffee, while citric and malic acids are primarily responsible for fruit-like brightness in the cup.

What is chlorogenic acid in coffee?

Chlorogenic acids are the most abundant acids in green coffee beans. They break down during roasting into quinic acid and caffeic acid, contributing to bitterness, body, and the coffee’s antioxidant properties. Lighter roasts retain more chlorogenic acid, while darker roasts contain more of the breakdown products.

Is acidity in coffee the same as sourness?

No. Sourness is a defect caused by under-extraction, immature beans, or poorly handled processing. Acidity in specialty coffee is a positive quality it is intentional, structured, and adds brightness to the cup rather than an unpleasant sharpness.

Does roasting affect acidity in coffee?

Yes. Lighter roasts preserve more of the bean’s natural organic acids, producing brighter, more vibrant flavours. As roasting progresses, heat breaks down these acids and as a result, medium and dark roasts tend to be lower in acidity and fuller in body.

Now that you understand what the acids in coffee are, the next step is learning how to taste them. Read Part 2: How to Taste Acidity in Coffee to develop your palate.

Sources

• Rivera, J.A. Alchemy in the Roasting Lab: Discovering Organic Acids (Parts 1 & 2), Roast Magazine, March/April 2005
• Specialty Coffee Association: Acids in Coffee — A Review of Sensory Measurements and Meta-Analysis of Chemical Composition, 2021
• routescoffee.co.uk