In short: coffee tastes bitter mainly because of chlorogenic acids, which account for 60–70% of its bitterness and break down during roasting into bitter lactones and, in dark roasts, harsh phenylindanes; caffeine adds only about 10%. In the cup, bitterness usually means over-extraction: grind coarser, shorten the brew and keep water at roughly 90–95 °C.
| Share of bitterness from chlorogenic acids | 60–70% |
|---|---|
| Share of bitterness from caffeine | about 10% |
| Chlorogenic acid content | arabica 5.5–8%, robusta 7–10% |
| Caffeine, robusta vs arabica | up to about 2x more in robusta |
| Recommended water temperature | approx. 90–95 °C |
| Espresso extraction time | beyond 30 seconds usually turns bitter |
Bitter coffee is rarely the bean's fault: in most cases it is over-extraction. When the grind is too fine, water passes slowly and pulls out the bitter compounds that come last, mainly caffeine and the breakdown products of chlorogenic acids. The other two culprits are water above 96 °C and a very dark roast. Below you will find how to tell which cause you are dealing with and how to fix it in the cup.
IS THE BITTERNESS OF COFFEE BAD?
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.
PERCEPTION OF THE BITTER TASTE OF 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.
THE BITTERNESS AND COMPOSITION OF THE COFFEE
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".
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.
DOES ROASTING INCREASE THE BITTERNESS OF COFFEE?
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 BITTER TASTE OF CAFFEINE
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.
HOW TO AVOID A LOT OF BITTERNESS IN YOUR CUP OF COFFEE
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.
HOW TO PREPARE COFFEE THAT IS NOT BITTER
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 |
BITTERNESS IN COFFEE - SUMMARY:
-
- Coffee robustacontains more chlorogenic acid and caffeine, so it will taste more bitter than coffee arabica.
- Roasting time and temperature affect the degradation of chlorogenic acid, which is converted by roasting into the corresponding lactones that cause coffee bitterness.
- Dark roast coffee contains phenylindanes, which cause undesirable bitterness.
- Caffeine promotes the perception of bitterness in coffee, but is not the main reason why coffee is bitter.
- Coffee preparation can increase the bitterness of a cup of coffee.
- Overextracted coffee results in bitter tasting coffee.
- Adjusting aspects of coffee preparation, such as extraction time, grind level, or water temperature can reduce the bitterness in your cup of coffee.
Frequently asked questions
Is coffee bitter or acidic?
Both at once, and the balance depends on extraction. Under-extracted coffee tastes sour and thin, over-extracted coffee tastes bitter and harsh. A correctly extracted cup is sweet in the middle with clean acidity.
What causes bitterness in coffee?
Over-extraction above all. Bitter compounds dissolve late in the brew, so too fine a grind, too long a contact time or water that is too hot drag them into the cup. Dark roasts add their own bitterness from degraded sugars.
How do you make coffee less bitter?
Grind coarser, shorten the brew and drop the water to 92 to 94 °C. If it still bites, move to a lighter roast. A pinch of salt reduces perceived bitterness, but it treats the symptom rather than the cause.
Why is my espresso bitter?
Usually the grind is too fine or the dose too large for the basket, which pushes extraction past 30 seconds. Check the group head as well: built-up rancid oils make every shot taste bitter.
Does the roast level change bitterness?
Considerably. Light roasts keep more acids and taste brighter, dark roasts develop bitter compounds during roasting. If you dislike bitterness, a medium roast is the safest starting point.
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