Introduction:Acidity is one of the key factors influencing the flavor profile of coffee, but many people have misconceptions about acidity in coffee, believing that sourness equals staleness or poor quality. In fact, acidity can be divided into pleasant fruity acidity and unpleasant astringent sourness, and the difference is closely related to roasting, variety, and brewing methods. This article will break down the sources of coffee acidity from a scientific perspective and teach you how to distinguish high-quality fruity acidity from undesirable sourness through sensory perception, thereby enhancing your coffee tasting ability.

Is the acidity in coffee a plus or a minus? Some drinkers believe that acidity indicates the beans are not fresh enough, while others see it as the soul of specialty coffee, capable of bringing out floral and fruity aromas and layers of flavor. In reality, green coffee beans are naturally rich in various organic acids, but during the roasting process, most acids gradually decompose or evaporate, leaving only a few types that can remain in the roasted beans.

According to professional research and cupping experience, there are not many types of acidity that human taste buds can clearly identify. Many of what we assume to be “fruit acids” are actually a composite sensation of acidity interacting with sweetness and aroma. To more accurately evaluate the acidity of coffee, the SCA (Specialty Coffee Association) has divided acidity in the latest cupping form into two main categories: “sweet-type” and “dry-type,” helping evaluators more clearly judge the quality of the acidity.

So, where does the acidity in a cup of coffee actually come from? Green coffee beans originally contain a variety of organic acids, including chlorogenic acid, quinic acid, citric acid, malic acid, phosphoric acid, acetic acid, and lactic acid. However, when the beans are subjected to high-temperature roasting, most acids are reduced or volatilized due to heat, and the ones that ultimately remain and have a real impact on flavor are mainly chlorogenic acid, quinic acid, citric acid, malic acid, phosphoric acid, acetic acid, and lactic acid.

Among them, chlorogenic acid itself is not water-soluble and cannot directly bring about acidity, but it can make the tongue feel a rough sensation; quinic acid is a degradation product of chlorogenic acid during roasting, is non-volatile, and often carries a bitter taste. Therefore, the ones that truly affect the taste of coffee acidity are primarily citric acid, malic acid, phosphoric acid, acetic acid, and lactic acid.

However, according to a study conducted by CoffeeMind in collaboration with the University of Southern Denmark, things aren’t that simple. The researchers roasted coffee beans from Kenya, Bolivia, and Brazil at three different levels—light, medium, and dark—and then conducted cuppings, measuring the actual concentrations of various organic acids in the coffee liquid and comparing them with the sensory thresholds at which humans can perceive those acids.

The results showed that, in addition to citric acid and phosphoric acid, acids such as acetic acid (vinegar), lactic acid, and malic acid, although they do exist in the coffee liquid, often have concentrations below the threshold detectable by human taste buds. This means that some of the “fruity acidity” we perceive when drinking coffee, such as the tangy-sweet taste resembling apples or Yakult, may not actually come from those specific organic acids themselves.

So why can we still perceive fruit-like acidity? According to the definition in the latest SCA cupping form, this is actually a form of “sensory association.” When the acidity in coffee interacts with other sensory signals such as sweetness and aroma, our brain automatically combines these signals to create an association similar to that of a certain fruit or beverage. For example, when a cup of coffee has light acidity accompanied by a bright sweet sensation, we might associate it with the taste of lemon juice or berries.

Then, in actual tasting, how should we judge whether the acidity in a cup of coffee is good or bad? In the past SCA cupping system, acidity used to be an independent scoring item, but as research deepened, experts found that the evaluation of acidity quality could not be separated from the overall flavor profile. Therefore, the latest version of the cupping form has integrated acidity into the overall sensory experience and further subdivided it into “sweet-type acidity” and “dry-type acidity.”

The so-called “dry-type acidity” is usually negative, with common manifestations including herbaceous sharp acidity (possibly originating from unripe or low-quality beans), astringent sourness resembling chewing on grass (common in under-roasted beans with raw cores), or wine-like sharp acidity (often caused by too light roasting or incomplete development). This type of acidity often leads to an unpleasant mouthfeel and can even carry an uncomfortable astringency.

In contrast, “sweet-type acidity” is a positive characteristic, typically manifesting as a juicy, bright, and refreshing acidity that can bring out fruity sweet notes. This type of acidity often appears in coffee beans grown at high altitudes and with good maturity, because the high-altitude environment allows for more sufficient sugar accumulation in the coffee fruit and also fosters a more balanced sweet and acidic expression.

In summary, the acidity in coffee is not a single indicator, but a complex sensory experience influenced by the interaction of multiple factors. Learning to distinguish the types and sources of acidity can help you more accurately select the coffee flavors you like and adjust brewing parameters to highlight or suppress specific acidity traits, making every cup of coffee more in line with your taste expectations.

The above content is compiled by CoffeeHunters, a coffee news website.