Why coffee is bitter and how to influence the bitterness in coffee


When making coffee ,you have a great chance toinfluence its taste yourself. By choosing the coffee and preparing it yourself. When we prepare coffee, the hot water extracts substances from the ground roast. Aperfect extraction is generally considered to be one that is balanced. We mean a coffee in which all the flavours are harmonious, complementary and balanced.

Aperfectly extracted coffee is enticingly sweet, with a sparkling acidity and a bitterness that adds depth. If you understand how extraction works, you can deliberately vary certain factors that influence the extraction process - the amount of coffee, the temperature of the water, the grinding, the extraction time, etc. This will contribute to the greater or lesser acidity and bitterness of such coffee.


In extraction, we are thus working with the flavours of the coffee that are already present in the coffee. That is to say, thesubstances in the coffee, which we then perceive as bitterness and other flavours. Although the preparation has a significant impact on how the coffee will taste, it onlyworks with what is inside the bean. Of course, the extraction and subsequent taste is also affected by thecomposition of the water used, which is often overlooked.

However, if we go further back to the origins of flavour in roasted coffee beans, we find that the roasting process has created a marked change in the composition of the roasted bean. Again, even with roasting, a roasting curve tailored to the coffee can mean a roast that brings out the unique potential of the coffee contained in each green bean. The origin of coffee flavour is encoded in the green coffee itself, influenced by its processing, growing conditions and the characteristics of the species of the parent coffee plant.


Green coffee is the seed of the fruit of the coffee tree. Itis therefore a fruit - a coffee cherry. As a fruit, coffee has both a natural sweetness and a typical fruity acidity. But where does the bitterness in coffee come from? For me, the fact that coffee contains thousands of chemical components is absolutely fascinating. For scientists investigating the mysteries of coffee, this fact is a "nut".

Roasted coffee is the origin of the fruit. Juicy, sweet notes are a given, but bitterness is also natural to it. Image source: Canva pro

So far, we can't define with complete accuracy all the reasons for coffee's bitterness. However, some of this bitter secret has already been revealed. Themost important factor causing coffee bitterness is chlorogenic acid. This acid is responsible for60-70% of the bitterness in the taste of coffee. Chlorogenic acid (CGA) is an ester of caffeic and quinic acid. Arabica coffee contains 5.5-8% of this acid and robusta coffee 7-10%.

Coffee in particular has the highest concentration of chlorogenic acid of the plant kingdom, which is known for its many health benefits for humans. Such as its anti-inflammatory effect or as a prevention of type 2 diabetes. Interested in other health benefits of coffee? Read our articles on caffeine, coffee and health.


What does chlorogenic acid have to do with coffee bitterness? It has a specific reaction when roasted. Specifically ,during roasting, this acid breaks down into lactones, which we then perceive as coffee bitterness. A subtle coffee bitterness that we want to let ring out in our cup for a complex taste experience.

But what happens if we let the spell that converts the acid into bitter lactones work too long or too aggressively? When roasted for longer or at higher temperatures, it breaks down further and forms metallic bitter phenylindanes. These phenylindanes are behind the unforgiving bitterness of dark roast coffees that can only be drunk with a good dose of sugar, milk and a slice of cake to fix the taste.


The amount of chlorogenic acid in coffee is therefore the primary influence on whether the coffee tastes bitter. There are other substances in coffee that contribute to the perception of bitterness. One such substance is - and we coffee lovers are all familiar with it - caffeine. Not so long ago, the bitterness of coffee was attributed to caffeine.

However, anyone who has tasted decaffeinated coffee knows that bitterness can be found there too. Caffeine promotes bitterness in coffee, but its contribution to the overall perception of bitterness in coffee is only 10%. Robusta coffee contains up to about 2x more caffeine and also more chlorogenic acid than arabica coffee, so it's no wonder it tastes much more bitter.

Caffeine is one of the reasons why coffee is bitter. However, it is not the main component of your coffee's bitterness. Image source Canva pro


So,whether you will have bitter coffee in your cup depends on your choice of roasted beans. What kind of coffee it is and how it was roasted. In the next step, the bitterness depends on how the coffee is prepared. As I described at the beginning of the article, by adjusting the brewing parameters you can influence how your coffee tastes. Whether it will be sour, bitter or perfectly balanced with a distinct sweetness.


Have you chosen light roast 100% Arabica beans and the coffee tastes very bitter? High bitterness caused by coffee preparation is a sign of over-extraction. Checkthese variables that are the main culprits of bitter coffee during preparation:

Extraction time extract the coffee for a shorter period of time
degree of grinding grind the coffee coarser
water temperature choose cooler water (within the recommended range of approx. 90-95 °C)
brewing method try a method with a shorter extraction time
amount of coffee did you use too much coffee? A larger quantity promotes strength and bitterness
purity residue from previous coffee on your drip tray or coffee machine lever can literally bitter the taste of the coffee you brew


    1. Coffee robustacontains more chlorogenic acid and caffeine, so it will taste more bitter than coffee arabica.
    2. Roasting time and temperature affect the degradation of chlorogenic acid, which is converted by roasting into the corresponding lactones that cause coffee bitterness.
    3. Dark roast coffee contains phenylindanes, which cause undesirable bitterness.
    4. Caffeine promotes the perception of bitterness in coffee, but is not the main reason why coffee is bitter.
    5. Coffee preparation can increase the bitterness of a cup of coffee.
    6. Overextracted coffee results in bitter tasting coffee.
    7. Adjusting aspects of coffee preparation, such as extraction time, grind level, or water temperature can reduce the bitterness in your cup of coffee.

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