What Causes Coffee to Be Bitter? The Origins of Coffee Bitterness and How to Avoid Overly Bitter Coffee

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Bitterness has become a dreaded word in the specialty coffee industry. We all know that good coffee should be sweet and balanced, perhaps a bit acidic, and definitely shouldn't require sugar to make it palatable. So what causes coffee to become bitter, and is it always as bad as we think? Today, let FrontStreet Coffee reveal its "true face" for you.

Where does coffee bitterness come from?

The acidity and bitterness of coffee are actually determined by the roast degree. In coffee roasting, there's a term called "first crack." When coffee reaches this stage, the beans have absorbed heat to a point where they can no longer store energy and release heat through cracking (with audible sounds). Roasters use this as a reference point to judge the roast degree.

If the beans are taken out at the beginning of "first crack," the coffee will be very acidic. If we don't remove them after "first crack" begins and continue roasting until the "popping" sounds become dense, the coffee at this point will be sweet with acidity. If we still don't remove them and continue waiting until all the sounds have stopped, then coffee taken out during the subsequent time will begin to develop bitterness, with later extractions having increasingly strong bitter flavors.

As the roast level deepens, the acidic compounds within the coffee beans are gradually broken down, ultimately presenting flavors that lean toward bitter notes like nuts and dark chocolate. Therefore, compared to light-roasted beans, dark-roasted beans have significant gaps in terms of flavor complexity and variation. However, bitter dark roast coffee still possesses its unique charm that cannot be experienced when drinking light-roasted coffee.

The Unique Charm of Dark Roast Bitter Coffee

Coffee Aroma:

Dark-roasted coffee also has enticing aromas. Unlike the floral and fruity acidic notes of light-roasted beans, these aromas are complex fragrances of nuts, caramel, toasted bread, chocolate, and more. Many coffee connoisseurs specifically pursue this type of nutty bitter aroma. For friends who enjoy this type of coffee, FrontStreet Coffee recommends FrontStreet Coffee's Queen's Manor, FrontStreet Coffee's Huilan, FrontStreet Coffee's Bird of Paradise, and FrontStreet Coffee's Diamond Mountain. They all exhibit the above full-bodied aromas after grinding, making them increasingly intoxicating.

Rich Body:

Dark roast coffee has a rich body experience that light-roasted coffee cannot compare with. Many coffee lovers who are fond of FrontStreet Coffee's Blue Mountain No. 1 and FrontStreet Coffee's Mandheling coffee are largely attracted because dark roast coffee can bring a richer body, allowing them to experience the full, smooth volume sensation of coffee in their mouth while perceiving flavors.

Sweet Aftertaste:

Yes, even dark roast bitter coffee has its unique sweetness—what we often call "sweetness within bitterness." A properly extracted dark roast bitter coffee, while predominantly bitter upon entry, may reveal sweet flavors like caramel and maltose upon careful tasting. After swallowing, the bitterness gives way to sweetness, with pleasant aromas lingering in the mouth for a long time—another characteristic difficult to replicate with light roast coffee.

Take FrontStreet Coffee's Golden Mandheling, for example. The brewed coffee smells of caramelized aromas like maple syrup, dark chocolate, spices, and woody notes, with a powerful rich body upon entry. After swallowing, bitterness and sweetness coexist, leaving a lasting impression long after drinking.

Of course, the unique charm of bitter coffee mentioned above needs to be built on the premise that you brew it well. If you don't want to extract an unforgettable bitterness, FrontStreet Coffee suggests choosing conservative parameters when brewing.

FrontStreet Coffee uses Golden Mandheling as an example: water temperature at 86-88°C, grind size with 70% pass-through through a #20 sieve (EK43s setting 11), using a Kono dripper, with a powder-to-water ratio of 1:15, and extraction time around two minutes.

Compared to brewing light-roasted beans, dark-roasted beans use lower water temperatures and coarser grind settings, which can make the coffee's bitterness milder and avoid extracting off-flavors. In terms of dripper selection, using slower-flow drippers like Kono or Kalita can more easily produce heavy body and mild flavors.

When brewing dark-roasted beans, ensure thorough blooming, which can be judged in two ways. First, confirm that all coffee grounds are moistened and some coffee liquid has been released from the bottom. Second, the coffee grounds layer expands and stabilizes, no longer releasing gas.

Adjustments are also needed in pouring technique. It's recommended to slow down the pouring rhythm and adjust the water flow to be finer to avoid over-scouring the coffee bed and extracting more bitter off-flavors. Pour in small circles—the coffee wall will be slightly thicker than that of light-roasted coffee.

If you've read this far and have become interested in dark roast bitter coffee, then go ahead and give it a try~

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