Bitterness has long been a controversial aspect of specialty coffee. High-quality coffee is often expected to be aromatic, naturally sweet, and well-balanced, with no need for added sugar.
But what exactly causes coffee's bitterness, and is it truly undesirable? Let's explore the science and nuances behind coffee's bitter taste.
Why Does my Coffee Taste Bitter, Sour or Burnt? #coffee
Video by Coffee Coach | Ryde Jeavons
Is Bitterness Always Bad?
Bitterness isn't inherently unpleasant. In fact, a touch of bitterness enhances coffee's complexity and balance, preventing it from being overly sweet or acidic. The key lies in moderation. A mild bitterness can complement coffee's other flavors, creating a richer experience.
Interestingly, most people find strong bitterness in coffee more tolerable than intense sourness. However, excessive bitterness can indeed ruin a cup of coffee. Understanding its origin and learning to manage it during preparation are crucial steps in mastering coffee brewing.
What Is Bitterness?
Bitterness is a familiar taste sensation, yet it varies among individuals due to differences in sensory perception. While one person might detect a bitter note, another might not. Taste perception involves more than just the tongue—it encompasses smell, mood, and even external factors like music or altitude, though this article focuses solely on the science of taste.
The Science of Bitterness
Previously, it was believed that different parts of the tongue were responsible for distinct tastes, such as sweetness, saltiness, sourness, and bitterness. Modern research shows that all areas of the tongue can detect these tastes.
Bitterness arises from interactions between compounds in food and proteins in our taste receptors. According to the American Institute for Quality and Efficiency in Medicine, approximately 35 proteins react to compounds in coffee, creating the perception of bitterness.
In coffee, this bitterness primarily stems from a group of compounds known as phenolic acids, particularly chlorogenic acids. In Arabica coffee beans, chlorogenic acids constitute about 8% of the bean's content and significantly impact its flavor profile.
Among the various types of chlorogenic acids, di-CGA stands out as a major contributor to coffee's bitterness. While quinic acid, derived from chlorogenic acids, is the primary source of bitterness, caffeine also plays a minor role.
Bitterness in Green Coffee Beans
When discussing bitterness, roasting often takes center stage, but some coffee beans are naturally more bitter than others.
For instance, Robusta coffee is notably more bitter than Arabica. This is due to higher levels of chlorogenic acids (10% in Robusta compared to 2% in Arabica) and nearly double the caffeine content.
Other factors also influence bitterness. A study published in the Brazilian Journal of Plant Physiology in 2006 highlighted how genetic traits, bean maturity, environmental conditions, and cultivation methods impact the levels of quinic acid in green coffee beans. For example, immature coffee cherries contain more quinic acid, explaining the harsher bitterness of coffee brewed from unripe beans.
Does Roasting Increase Coffee's Bitterness?
Roasting triggers chemical changes in chlorogenic acids. While chlorogenic acids themselves aren't bitter, their breakdown during roasting produces compounds like chlorogenic lactones and phenylindanes, which contribute to bitterness.
A 2007 study by Thomas Hofmann revealed that lighter to medium roasts contain more chlorogenic lactones, described as delivering a "pleasant, high-quality bitterness." Darker roasts, on the other hand, generate phenylindanes, which create a stronger, lingering bitterness.
Thus, lighter roasts tend to have lower bitterness and retain more of the beans' original flavors and aromas. However, taste is subjective, and what one person finds unpleasantly bitter might be enjoyable to someone else.
How to Minimize Bitterness When Brewing
Even if you start with high-quality, lightly roasted Arabica beans, the brewing technique greatly influences the final taste. Over-extraction is a common cause of excessive bitterness, as bitter compounds are released during the latter stages of brewing.
Key factors affecting extraction include brewing method, grind size, water temperature, and brewing time. Here are some tips for achieving better balance:
1. Grind Size: Finer grinds increase surface area, leading to quicker extraction. While this can create a stronger brew, it also heightens the risk of over-extraction and bitterness. Adjust grind size to suit your brewing method.
2. Water Temperature: Higher temperatures extract more compounds from the coffee, including bitter ones. For beans with naturally strong bitter notes, try brewing at slightly lower temperatures.
3. Brewing Time: Longer brewing times can lead to excessive bitterness. If your coffee tastes overly bitter, consider reducing the steeping or extraction time.
4. Balance: Adjusting one variable, such as grind size, affects others, like brewing time. Experiment to find the right combination that highlights your coffee's desired flavors.
Final Thoughts on Bitterness
Bitterness isn't always a flaw; it can enhance coffee's complexity when balanced correctly. Understanding its origins—from bean composition to roasting and brewing techniques—enables better control over the final flavor.
By following these recommendations and experimenting with different variables, you can discover a perfectly balanced cup tailored to your preferences, appreciating the role bitterness plays in crafting a satisfying coffee experience.
