Acidity. A common topic of conversation among coffee lovers. The conversation then usually revolves around the roasting level of the coffee. The more intensely roasted, the less acidic the coffee tastes. While this is broadly true, there is more to be said on this subject.

What are you actually tasting?

Ever walked into a specialty coffee bar and ordered a double espresso or americano? Chances are you thought this coffee tasted rather sour. The substances responsible for this are organic acids. The most common are malic acid and citric acid. But also acetic acid, lactic acid, caffeic acid, quinic acid and phosphoric acid all contribute to the acidity of the coffee.

How do these acids get into the coffee?

The two most common acids, malic acid and citric acid, occur naturally in plants and play an important role in photosynthesis .

The environmental factors and terroir are also very important for the composition of the organic acids in coffee. For example, phosphoric acid is a typical acid that is mainly present in Kenyan coffee.

Fermentation is another source of organic acids. During the fermentation process, sucrose will convert into acetic acid, lactic acid and formic acid. Partly because of this, the fermentation process plays an important role in the final taste of the coffee.

Many of these acids are broken down during roasting. The amount of citric acid, malic acid and phosphoric acid decreases as the roast level increases. Acetic acid, lactic acid and formic acid initially show a small increase, but also decrease at higher temperatures. The origin of this initial increase has also to do with sucrose, which is also partly converted into these acids during roasting . Finally, caffeic acid and quinic acid are both formed by the breakdown of a different type of acid during roasting and therefore increases and then decreases again at higher temperatures.

Fact and Fiction

Although recognizing certain acids in coffee has long been an integral part of various international tests, this has come under fire recently. You can only detect a certain acid in coffee from a certain concentration. If the coffee contains too little of this acid, you cannot detect it. What does research now show; the amount of acids (with the exception of citric acid) in all coffees is too low for a human to perceive. So what we mean when we taste acidity in coffee is a lot more complicated than we thought. Take Kenyan coffees and Brazilian coffees as an example. Ask any barista which of these 2 coffees contains the most acidity and they will tell you unanimously that Kenyan coffees tend to contain more acidity and fruitiness. But Kenyan coffees often contain less citric acid than Brazilian ones. Clearly there is more going on here. Perhaps the combination of certain acids provides a strengthening effect that makes us taste them faster? This appears to be the case with citric acid and malic acid . Phosphoric acid also has this effect in combination with other acids. Another explanation why Brazilian coffees are perceived as less acidic could be found in caffeic acid and quinic acid. These bitter acids may obscure the acidity of citric acid. In any case, the world of acidity in coffee is not as simple and obvious as originally thought.

What does this mean for us? Not that much actually. You should never forget that coffee is first and foremost a good thing to drink and not a strick science thing. Let the scientists do their thing, we'll just taste and enjoy it ;)