ENGLISH | 中文 | عربى

Bitterness: Finding the Right Balance

Many people don't drink coffee because of its bitter flavor, yet at the same time, a lot of people love to drink  coffee for this exact reason!

But we should ask ourselves, is bitter coffee better? Is bitter good or bad? Where does this flavor come from? Is coffee supposed to taste bitter?  What flavors can we balance and pair together with bitterness to create new and interesting experiences?

 Today, we will answer these questions and more as we explore this bold flavor we refer to as “bitterness”.



What is “Bitterness”?


First, let’s talk about what “bitterness” means.  No, we aren’t talking about that feeling you get when your lover dumps you in public at dinner, or even fighting to the bitter end for that last piece of cake at the office party—no matter how long it takes or the cost!


No… What we are talking about here are the “bitter” flavors we experience—you would never mistake them for sweetness or anything else!  Our sensitivity to these bold flavors is estimated to be the result of evolution, an adaption we made to ensure our survival and avoid harmful or poisonous things.


Bitterness can be very unpleasant, but when blended with other flavors, it can actually be quite pleasant.  Think about your favorite brand of dark chocolate—the slightly sweet flavors combined with the bitterness are loved by chocolate connoisseurs.  An even better example might be beer, especially craft beer.  Recently, the market has seen a huge rise in popularity of IPA (India Pale Ale).  The “hoppy”, bitter flavors of this beer combine with the fizzy mouthfeel and sweetness to result in a myriad of different IPAs.


What would dark chocolate taste like if it wasn’t bitter?  How about beer?  Would people still like these products if they didn’t have this bitter flavor?


What do you think?


How We Experience Bitterness


To understand how and why we perceive bitterness, we need to turn to science to answer the technical questions.


Taste is the sensation produced when a substance in the mouth reacts chemically with taste receptor cells located on taste buds in the oral cavity, mostly on the tongue. Taste, along with smell (olfaction) and trigeminal nerve stimulation (registering texture, pain, and temperature), determines flavors of food or other substances. 


The sensation of taste includes five basic tastes: sweetnesssournesssaltinessbitterness, and savoriness [or Umami ].[6][7] Scientific experiments have proven that these five tastes exist and are distinct from one another.[citation needed] Taste buds are able to distinguish between different tastes through detecting interaction with different molecules or ions.


The bitter taste is almost universally unpleasant to humans. This is because many nitrogenous organic molecules which have a pharmacological effect on humans taste bitter. These include caffeinenicotine, and strychnine, which respectively compose the stimulant in coffee, addictive agent in cigarettes, and active compound in many pesticides.


It appears that some psychological process allows humans to overcome their innate aversion to bitter taste, as caffeinated drinks are widely consumed and enjoyed around the world. It is also interesting to note that many common medicines have a bitter taste if chewed; the gustatory system apparently interprets these compounds as poisons. In this manner, the unpleasant reaction to the bitter taste is a last-line warning system before the compound is ingested and can do damage.


It was originally thought that different areas of the tongue register different tastes, but it has been proven that different areas of the tongue can tastes all flavors. This is because our tongue's sensory cells contain many different proteins, about 35 of which react with certain compounds in foods and drinks to produce a bitter taste.


For coffee, the amount of these compounds directly determines the final bitterness we experience. These compounds are collectively referred to as phenolic compounds.




What Causes Bitterness in Coffee?


So where does coffee's bitterness come from?

The quality of green beans, the roasting process and brewing method can all impact the bitterness of coffee in the cup.


Green Bean


One of the main compounds in coffee beans that produces bitter flavors is chlorogenic acid. Chlorogenic acid is one of the many organic acids that coffee produces as it grows.


Chlorogenic acid itself is very bitter, but during roasting and brewing it also will break down into quinic acid and caffeic acids, which are also bitter.

The variety, age, external conditions and farming methods (among myriad other factors), will affect the chlorogenic acid content in green beans. The different processing methods can also impact the chlorogenic acid content.

Besides chlorogenic acid, caffeine itself also has a strong bitter quality.

Caffeine is a plant alkaloid, and you can find it in many plants (like tea). This bitter alkaloid is a natural pesticide that deters insects from eating the plant. Human consumption of caffeine, mainly as a "stimulant", can help reduce fatigue and drowsiness.


Caffeine is structurally similar to Adenosine, which accumulates while we are awake and then binds to adenosine receptors, causing us to become drowsy, signaling that we need rest. But caffeine blocks these adenosine receptors, allowing humans to maintain focus and alertness.


Of the world's two most commonly consumed coffees, Arabica and Robusta, Robusta has almost twice the amount of of caffeine and chlorogenic acid. Robusta also has half the sugar content, which means its bitterness is not modulated well, resulting a more pronounced bitter flavor.



Many chemical reactions occur during roasting, and the organic acid content in green beans changes with the roasting process. From light to dark roasting, the degree of bitterness increases, because chlorogenic acid breaks down during roasting, and continues to break down during brewing, to produce bitter quinic acid and caffeic acid.


.You not bring into account dry distillation flavors and char flavors at all


During the baking or roasting process of food or coffee, the organic acid, sugar and bitter compounds will change during chemical reactions, such as caramelization and the Maillard reaction. At the same time, the flavor modulation will change as the makeup and proportions of different chemical compounds change.


In order to understand more about how carmelization and flavor modulation can impact aromas and tastes, we did some simple experiments. We’ve included the results below.


Experiment 1 

Compare sugar carmelizing, 

bread baking and the coffee roasting process.



We found the following similarities with the roasting process, summarized below:


1. Color changes: 

We can clearly see from the photos that the color all change from light to dark, all of them experienced the browning and end up with charring.

2. Aroma changes: 

During the roasting process, the aroma changes from the pleased aroma to smoky and tar.

3. Flavor changes: 

See the charts below for details.


At a certain point during the roasting process, heat will help convert sugar into volatile aromatic compounds (VAC). Compounds will has display bolder smells, and although they technically contain less sugar, will actually taste sweeter. As the roasting process continues, it will start to display more bitterness and less sweetness, eventually resulting in a charred flavor.


Experiment 2

Coffee brewing and extraction

When lightly roasted, the same green beans might not be bitter at all, because the brewing method can affect which soluble substances are extracted first and later.  Soluble substances in coffee account for 30% net weight of the bean.  Those with lower molecular weight will be extracted first, while bitter compounds tend to be extracted later.  



From the traditional SCAA flavor wheel, we can see that enzymatic, caramelized and dry distillation flavor compounds in coffee are the positive flavors we experience. So as we extract, we first produce sour flavors, then sweet, and finally bitter flavors. 


If the green beans and roasting conditions are exactly the same, then the higher the extraction rate, the more bitter the coffee will taste. The factors that affect the extraction of coffee mainly include coffee ground fineness, water temperature, water quality, time, turbulence (rate of water passing through and over the coffee), coffee brewing tools and methods.


If the bitterness in a cup of coffee is too high, you can try to reduce the bitterness by changing these variables.  We recommend you give this a try in your shop or at home!


We can use some experiment to see what flavor will come out first and late during the coffee extraction process.


La Marzocco PB Espresso Machine, Mahlkonig Grinder

Bean: Torch Coffee 99 Espresso Blend, 18g Coffee

1. Taste the coffee from 0-10s, 10-20s, 20-30s. Then test TDS.


2. Use same dose, extract 10s, 20s, and 30s, taste it and see the difference.  Test TDS.


3. Use same dose, extract 10s, 20s, and 30s, then combine with same amount of milk. Taste it and see the difference.


So, from this experiment we can see, there are more sour and sweet flavors during the early extraction, more bitterness will occur later in the extraction process. Only bitterness modulated with sour and sweetness, such as coffee and milk, can have more balanced and complex flavor.



So is Bitterness in Coffee Good or Bad?


Let’s think about this for a moment… what would happen if coffee did not taste bitter?


As with dark chocolate, the tastes of bitterness blends with sweetness, and different people prefer different proportions of bitterness to sweetness.  Hence the large range of different “pure cacao” contents of specialty dark chocolate. Different tastes combine together and harmonize to produce all the different flavors we experience, and hopefully enjoy.


The same can be said for coffees.  Different people prefer different flavors of coffees, and the way coffee and milk combine together combine to produce a new experience, so we don’t always consider the bitterness of coffee by itself, but instead how we experience it as a final product.


For roasters, baristas and coffee shop owners, we always need to consider how we serve it to customers, and how we want them to experience our coffee.


How you enjoy your coffee is ultimately up to you, but we hope this article has helped you understand the different ways you can produce the ideal flavor for you or your customers.  


Never stop learning!




Sources: https://en.wikipedia.org/wiki/Taste#Bitterness