Bitterness is one of primary taste characteristics of coffee. Other primary tastes, acidity, sweetness, saltiness, or sourness, doesn’t seem to represent coffee as well as the bitterness. I think this general recognition of coffee being bitter has a lot to do with the caffeine. Many drink coffee for pure joy like we do. Those who enjoy coffee know bitterness isn’t the only taste components. But at the same time, many drink coffee as a drug to wake themselves up with its caffeine. They don’t necessarily enjoy coffee, but they might rather connect the most difficult moment of the day and coffee. For them, coffee is for caffeine which they need at the bitter moment. That made coffee bitter.
The bitterness isn’t universally preferred taste unlike sweetness. For humans, bitterness and acidity are rather a dangerous hazard. It is biologically understandable that many people don’t like coffee because of the bitterness or acidity.
The caffeine is the best known substance contained in coffee and believed to be the source of bitterness. The caffeine is stable throughout various temperature. In green coffee beans, slightly over 1% of caffein is contained, or even in Italian roasted coffee, the caffeine content is aproximately 1%. At around 360F, some caffeine vaporazes, but it mostly remains in the coffee.
What interesting is that as roast level progresses, the coffee generally gets bitterer. If the caffeine is the main source of bitterness, the bitterness remains the same as the caffeine content is almost flat. It used to be expained that the caffeine’s vaporization generates a by-product which contains bitterness, but it’s much higher boiling point(at over 400C) and roasted beans caffeine content, it’s proved not to be the main source of bitterness. Furthermore, decaf coffee is also bitter.
The caffeine is definitely undergoing source of bitterness, which you could taste at at any roast levels. The study in other bitterness components have been conducted and understood gradually.
Other Bitter Source Appears in Roasting Process
The best possible candidate is whatever substance called DKP(Diketopiperazines). It’s also found in cocoa and dark beer as a source of bitterness. DKP is known to be generated from reaction caused by heat in some food, so the roasting presumably generates it. The bitterness of this substance varies depending on its specific kind, and it could be from the same level to 20 times as bitter as caffeine.
Another factor, the chlorogenic acids, shows acidity, sweetness, and bitterness based on its concentration. At brewing stage, it is well extracted at higher temperature and longer brewing time, and resulting cup tends to be bitter.
The caffeine is certainly a factor of bitterness in a coffee, but it isn’t the only factor. If you wanna wake yourself up, you need caffeine, but the strongly bitter coffee isn’t necessarily better at waking you up than lighter one.
Photo credit: Dru Bloomfield