Why Does American Coffee Have a Sour Taste? | Is It Okay to Drink Sour Coffee? | Understanding Coffee's Acidity

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Isn't Coffee Supposed to Be Bitter? Why Does Americano Have Acidity? Is Sour Coffee Still Drinkable?

When people who don't usually drink coffee suddenly encounter some specialty coffee, they're often filled with questions: Why! Isn't this stuff supposed to be bitter? Why is it so sour!

Simply put, this is because coffee contains rich organic acids, aromatic hydrocarbons, proteins, lipids, plant alkaloids, and sugars. Through chemical changes during roasting, various interesting aromas, acidity, sweetness, and bitterness are produced. Today, let's explore the various sour, sweet, bitter, and aromatic aspects of coffee beans! This knowledge can help everyone select coffee beans, roast raw beans, and brew coffee.

Healthy but Unpleasant Astringent Acid in Coffee: Chlorogenic Acid

Coffee is actually an acidic beverage, and an important part of tasting specialty coffee is appreciating its layered acidity. Most specialty coffees use Arabica coffee beans, while common commercial beans mostly choose Robusta coffee beans. Robusta coffee beans contain more chlorogenic acid, also called coffee tannic acid. This acid doesn't taste good, and insects don't like eating it, so Robusta coffee trees usually have better pest resistance.

Not only do insects dislike chlorogenic acid, but humans actually don't like its bitter and astringent taste either, although it's a good antioxidant that's beneficial to health. The good news is that chlorogenic acid transforms into quinic acid and caffeic acid during coffee roasting, which is one reason why darker roasts are less acidic.

Specialty coffee has relatively less chlorogenic acid, so light roasts won't be too harshly acidic, while Robusta coffee beans mostly use medium roasts or darker to avoid being unpleasantly sour. However, this is just a general trend and not absolute.

Wait, wait, wait! Isn't specialty coffee supposed to be more acidic? Then why does specialty coffee have less chlorogenic acid but still taste more acidic?

This is because the multi-layered, bright, and interesting acidity in specialty coffee is not created solely by chlorogenic acid's sourness. Chlorogenic acid is actually a bitter and astringent acid. The pleasant acidity in specialty coffee mostly comes from citric acid, malic acid, quinic acid, acetic acid, and tartaric acid, but it goes far beyond that, as coffee beans contain thousands of chemical substances that affect flavor. However, FrontStreet Coffee will introduce these main flavor-influencing acids today.

Malic Acid and Citric Acid That Don't Match Their Names

Malic acid and citric acid sound very youthful and colorful, but did you know? Actually, malic acid and citric acid don't have fruit aromas because they're non-volatile, so they can't be smelled. They're called malic acid and citric acid simply because apples and lemons contain abundant amounts of these two acids.

However! When malic acid and citric acid combine with alcohols, they can produce many captivating aromas such as floral, fruity, and fresh scents. This is the main source of aroma in both raw and roasted beans.

Also Quinic Acid and Tartaric Acid

Quinic acid is formed from the degradation of chlorogenic acid, and it's still uncertain whether it brings astringency to coffee or adds brightness to its flavor. Both views have many supporters, but the editor believes these two things don't necessarily conflict. Did you know? Actually, sophisticated perfumes add a bit of unpleasant odor to enhance the layered complexity of fragrances...

As for tartaric acid, it's commonly found in fruits like grapes and bananas and is also one of the main organic acids in wine. With these various acids, along with multiple sugars and lipids in coffee beans, various chemical changes occur to produce the countless variations of acidity, aroma, and sweetness.

The Relationship Between Acidity in Specialty Coffee and Sucrose

Interestingly, the bright, lively acidity in coffee is directly proportional to the amount of sucrose contained in the coffee beans, and the amount of sucrose in coffee beans is also closely related to origin and altitude.

For example, coffee beans from Kenya have very strong and distinctive acidity, with sucrose content reaching 8.45% by weight. The second highest is Colombia at 8.3%, which is why Colombian coffee beans are often used in espresso blends to balance acidity.

In terms of Africa, African coffee beans typically have higher sucrose content, along with noticeable fruit acids and fruit aromas. Next is South America, which has milder, less stimulating, and smooth acidic aromas.

Additionally, research has found that for every 100 meters increase in altitude, temperature decreases by 0.6 degrees Celsius, and for every 300 meters increase, the sucrose content in coffee beans increases by 10%. This is because higher altitudes have lower temperatures and greater day-night temperature differences, which can slow coffee's growth rate, allowing it to store more nutrients. During roasting, sucrose produces more acidic aromatic compounds, which is why high-altitude hard beans have far superior acidity and aroma than lower-altitude soft beans.

Roasting Removes Coffee's Acidity

Friends who have roasted their own beans know that the darker the roast, the more acidity in the coffee is destroyed, replaced by more caramel flavors, smoky notes, and bitterness. This is why specialty coffee rarely uses roasts darker than medium. Of course, rare doesn't mean impossible - dark roasting of specialty coffee beans is an interesting craft. Friends who roast their own beans can try experimenting with different roast levels of the same bean to see how the acidity changes.

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