Acidity is a term that’s often used to describe coffee, usually in a positive light. What does acidity refer to in coffee, though? Acidity is used to describe a range of flavors that are perceived in coffee and can be directly attributed to acids found in the coffee beans.
The Roasting Process Changes the Acids in a Coffee
Before looking at specific acids found in coffee, a refresher on high school chemistry may be in order. Simply defined, an acid is a substance that has a pH lower than 7, which means it gives off H+ ions in an aqueous solution. When we taste an acid, the H+ ions that it gives off activate neurons on the tongue, which, in turn, send signals to the brain that we associate with different flavors. The specific flavors we identify from an acid depend on its precise chemical makeup.
As green beans undergo chemical reactions in the roasting process, the concentrations of specific acids change. Most acids degrade at higher temperatures, but some increase. Generally speaking, the roasting process tries to bring out the best mixture of naturally occurring acids found in a specific coffee, as these are the compounds that give the coffee its unique characteristics.
Acids Found in Coffee and Their Characteristics
A number of different acids are found in coffee. In this survey, we’ll focus on the ones that survive the roasting process, as they are the acids that affect a coffee’s final flavor. The first ones listed below have a positive impact on a coffee, while those lower on the list can have good and bad effects.
Citric acid is found in arabica beans grown at higher elevations. The same acid that’s found in citrus fruits, this acid is associated with notes of lemon, orange and, when occurring with phosphoric acid, grapefruit.
Phosphoric acid tastes sweeter than most acids. It can turn an otherwise sour-tasting citrus flavor into a sweeter grapefruit- or mango-like one.
Malic acid is sometimes associated with hints of stone fruit, such as peaches or plums, but it’s more common to taste apple or pear in a coffee that has malic acid.
Chlorogenic acids (CGAs) are largely responsible for a coffee’s perceived acidity. Compared to other acids, they degrade rapidly in the roasting, which is why light roasts are described as “bright” and “acidic” more often than dark ones.
Acetic acid, which is the same acid that’s found in vinegar, may produce a pleasant sharpness at lower concentrations. Higher levels of acetic acid, though, are unpleasant. A coffee that has a lot of acetic acid probably wasn’t properly processed.
Tartaric acid, similarly, produces a sour taste at high concentrations. At low levels, however, it can offer up grape-like or winey notes, which isn’t surprising since it’s found in grapes.
Quinic acid is produced as other acids degrade. High concentrations of it are common in darkly roasted coffee, stale coffee, and coffee that was brewed several hours ago but kept warm on a hot plate. Although it gives coffee a clean finish, quinic acid is the main acid that turns stomachs sour.
Many of the tastes you identify in coffee can be directly attributed to the acids contained within them. If you can identify acids you prefer, then you’ll be able to look for coffees that have been grown or roasted in a way likely to produce those acids. Perhaps there was a reason to pay attention in eighth-period chemistry class after all.
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