What is acidity in coffee?
Among coffee professionals, acidity is generally considered a desirable sensory characteristic of speciality coffee. However, this is not necessarily the case for consumers.
The relevant basic tastes (detected on the tongue) for coffee are acidity, sweetness, bitterness. It is not uncommon for coffee drinkers to confuse acidity and bitterness. Acidity is the bright, tangy sourness you get from citrus fruits, like lemon or lime. Bitterness, on the other hand, is the harsher taste you might experience from burnt toast or unsweetened cocoa.
The organic acids found in green (unroasted) coffee vary depending on the coffee's species, variety, origin, altitude, and processing method. When coffee is roasted, the composition and concentration of these acids undergo significant changes. Some acids degrade, while others transform into new compounds that affect the coffee’s flavour. The primary acids in roasted coffee are chlorogenic, quinic, citric, malic, acetic, formic, and lactic acids.
There is a direct link between roast level and perceived acidity in a coffee. As the roast level of a coffee increases, the perceived acidity of the coffee beverage decreases. Drinkers that prefer less acidic coffee will prefer darker roasts, while those that like some acidity in their coffee will prefer lighter roasts.
A new scientific study has shown that the link between perceived acidity and the actual concentrations of acids in brewed coffee is not straight-forward.
Which acids are detectable in brewed coffee?
It has commonly been claimed that specific organic acids can be detected in brewed coffee. The Specialty Coffee Association (SCA) flavour wheel lists specific acids under a sour category, including Acetic, Citric and Malic Acid. Only recently has scientific research been conducted to test whether these acids can actually be tasted in brewed coffee.
The academic paper ‘Acids in brewed coffees: Chemical composition and sensory threshold’ by C Rune et al. has shown that of the main organic acids in coffee, only citric acid is present in brewed coffee at a perceivable level.
The organic acids that have previously thought to have been important in sensory analysis of coffee have been shown to not be perceptible in brewed coffee are Acetic, Lactic and Malic acid. Phosphoric acid was also shown to be present in brewed coffee at levels below the detection threshold.
This has several implications for coffee professionals. Firstly, within industry standard coffee training there are often sensory tests where students are asked to identify the intensities of specific organic acids dissolved in water. A test for overall acidity is reasonable – but the ability to identify specific acids isnt a skill that can be applied when tasting brewed coffee.
When describing coffees, it does not make sense to describe specific acids, except possibly for citric.
Acidity and Origin
Coffee of African origin are generally perceived as more acidic than Brazilian coffees. Is this reflected in the chemistry of brewed coffee from these origins?
The answer is unexpected – In the same research it was found that Brazilian Coffees had higher measured total acidity than the Kenyan coffee tested. This is contrary to common perception of Kenyan coffees having a higher acidity than coffees from Brazil. This illustrates that there isn’t a straight forward link between the acidity perceived when tasting coffee and the measurable acidity in the coffee.
This highlights the complexity of the sensory analysis of coffee. Factors other than the chemical acidity of the brewed coffee affect the drinkers perception of acidity. A possible factor listed in the article is cross-modal aroma-taste interaction – the Kenyan coffee has a fruity aroma and therefore the drinker perceives it as more acidic than the less fruity Brazilian Coffee.
Summary
Acidity in coffee is a desirable sensory characteristic among coffee professionals, although consumer preferences may vary. The roast level of coffee directly affects the perceived acidity, with darker roasts having lower perceived acidity compared to lighter roasts. While specific organic acids like acetic, lactic, and malic acid have been claimed to be detectable in brewed coffee, recent scientific research suggests that only citric acid is perceivable. Contrary to common perception, Brazilian coffees have been found to exhibit higher measured total acidity than Kenyan coffees, highlighting the complexity of sensory analysis. Factors such as aroma-taste interaction can influence a drinker's perception of acidity.
Now you know how to choose a coffee with the right acidity level for you, have a look at our coffee collection, paying special attention to roast level!
References
Birke Rune, C.J., Giacalone, D., Steen, I., Duelund, L., Münchow, M., and Clausen, M.P. (2023). Acids in brewed coffees: Chemical composition and sensory threshold. Current Research in Food Science, 6, 100485.