How Do Acids in Coffee Shape the Taste of a Cup?

Coffee tastes sour because the beans themselves contain a range of acids, and the roast level decides how much of that acidity survives to the cup. Before the specialty era, dark roasting was standard, and it broke down or masked many of these compounds. When lightly roasted coffee became common, the sourness that had always been present became easy to notice.

Acidity is not a goal in itself. What matters is acidity quality, not acidity level: intensity alone can read as sharp, while quality blends with sweetness and aroma to give citrus or dried plum notes. Growing altitude, soil fertility, processing method and brewing all influence how that acidity comes through in a lightly roasted coffee.

Many people feel confused when they taste acidity in coffee, but coffee beans themselves are rich in various acidic substances. Before the millennium, mainstream dark roasting broke down or masked the acidity, and only when light roasting became popular in the specialty coffee era did acidity become clearly perceptible. But coffee is not better the more acidic it is; what we should pursue is "acidity quality" rather than mere "acidity level." Acidity level refers to the intensity of sourness, and if it is too high, it becomes sharp and hard to accept; acidity quality, on the other hand, combines with other senses and can evoke positive flavors such as citrus and smoked plum. The quality of acidity is affected by many factors, including growing altitude, soil fertility, processing, and brewing. Front Street Coffee will break down these factors in detail in this article to help you truly understand coffee acidity.

In the article "Why Is Most Coffee Nowadays Acidic," Front Street Coffee already explained why most coffee has acidity. Afterward, many readers responded: I understand why coffee should be acidic, but a new question arises—why is coffee acidic?

The reason is actually not complicated, because coffee beans themselves contain a large amount of acidic components. Most people find it strange that coffee has acidity, mainly because before the millennium, the mainstream roast level tended toward dark roasting.

Dark roasting causes the acidic substances in coffee beans to continuously break down and transform into other components. Although they do not all disappear, the smoky aroma produced by dark roasting also masks the remaining acidity, which is why people in the past generally thought coffee was bitter rather than acidic.

After the arrival of the specialty coffee era, the mainstream roast level shifted from dark to light. With shorter roasting times, bitterness no longer masked everything, and only then did people taste acidity in coffee. However, coffee is not better the more acidic it is.

Why is coffee not better the more acidic it is?

Because what we want to perceive in coffee is "acidity quality," not "acidity level." Acidity level refers to the intensity of sourness in a cup of coffee.

As is well known, there are mainly four tastes people can detect in coffee: sour, sweet, bitter, and salty. These four balance one another. Once one taste far exceeds the others, its expression in the coffee becomes prominent and sharp, making it hard to accept.

Just like oranges and lemons, both of which are citrus fruits, one is pleasantly sweet and sour, while the other is stimulatingly sour; the difference lies in the acidity level. Front Street Coffee thinks very few people would bite directly into a lemon. So coffee is not better the more acidic it is.

Acidity quality refers to the sour sensation we experience in coffee by combining other senses in addition to our taste buds. Most flavors are associations we make after perceiving acidity quality. Therefore, acidity quality is the kind of acidity we want to taste in coffee.

However, acidity quality also has good and bad distinctions. Good acidity quality carries an obvious sweetness and can evoke rich fruit aromas, that is, a sweeter kind of acidity. For example, lighter ones include citrus, starfruit, pineapple... while deeper ones include smoked plum, purple grapes, ripe fruit... In short, it is acidity quality that can bring out positive flavors.

Bad acidity quality brings unpleasant tastes, such as the sourness people associate with herbs entering the mouth, or the sourness of a certain kind of vinegar, and if stronger, an acidic and astringent taste with obvious astringency.

It should be known that roast level is not completely the factor that determines whether coffee acidity quality is good or bad. Although roasting can steer the flavor direction of coffee, and the lighter the roast, the more acidic the coffee, as Front Street Coffee said earlier, the acidity we pursue is acidity quality, not acidity level. Therefore, the degree to which coffee should be roasted mainly depends on the roast level at which the coffee beans express themselves best.

The acidity quality we perceive in coffee is mainly formed through the breakdown and transformation of various organic acids after roasting. In other words, the amount of organic acids in coffee beans determines the degree to which acidity quality is expressed. It sounds a bit convoluted, but that is how it works.

The organic acid content of a coffee bean mainly depends on the altitude at which it is grown and the fertility of the soil, because these factors all positively contribute to the formation of organic substances in coffee beans. The higher the altitude and the more fertile the soil, the more organic acids the coffee beans can accumulate, and vice versa.

Front Street Coffee will give another more intuitive example to help understanding: if coffee beans grown at 1,600 meters are lightly roasted, they will show a very solid and full fruit-like acidity quality; but if the same beans are grown at 1,000 meters and then lightly roasted, the acidity they present will be very hollow, with no obvious fruit aroma and not much sweetness, with only pronounced nutty flavors. This is the gap brought by the growing environment.

Of course, whether the acidity quality of a cup of coffee is good or bad is not entirely determined by the growing environment. Coffee processing, roasting, and even brewing can all affect acidity quality. When mistakes occur in these "cooking" stages, acidity quality will develop in a negative direction, causing us to taste unpleasant negative flavors. Therefore, no matter which stage it is, it is best to stay fully focused during operation to avoid failure.

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