If you ask most people how to describe coffee and they’d say ‘bitter’. Bitterness is such an expected part of the coffee experience that we rarely stop to think, why is my coffee bitter? Is coffee inherently bitter or am I brewing it wrong? It is possible to make coffee that’s not bitter? Let’s dive into the science and try to answer, why is coffee bitter?
The Chemistry Behind Coffee
It all boils down to coffee. Bitterness in coffee is tied to the presence of phenolic compounds, the most prominent of which are chlorogenic acids. Chlorogenic acids account for most of the bitterness in coffee along with other sensory elements like flavor and aroma. Two of these chlorogenic acids are primarily responsible for bitterness: 5-caffeoylquinic acid and di-CGA. The former accounts for most bitterness.
Caffeine also plays a minor role in contributing to bitterness. Caffeine is a naturally bitter-tasting compound and higher concentrations of caffeine can lead to excessively bitter coffee.
Differences in caffeine concentration and amount of chlorogenic acids means that some varieties of coffee are naturally more bitter. Robusta, with higher caffeine content and higher concentration of chlorogenic acids, is generally more bitter than Arabica. Recent research has also suggested that other factors such as the environment, maturation, processing method, and genetics play a role in determining whether coffee tastes bitter.
What Makes Coffee Bitter
Roasting is a major factor in determining bitterness in your coffee. Heat applied during the roasting process causes degradation of the chlorogenic acids in the green beans and sets off a chemical change. These chlorogenic acids are converted into their corresponding lactones and phenylindanes. Chlorogenic acids themselves aren’t bitter (they actually taste sour) but these resulting lactones and phenylindanes impart bitterness.
Chlorogenic acid lactones are formed around the first crack, at 200°C. This means light and medium roast coffee has a balanced and mild bitterness, that’s often described as “coffee-like”. If the heating process is continued, these lactones turn into phenylindanes above 210-220°C. Phenylindanes have a harsher, long-lasting bitterness.
Why Does My Coffee Taste Bitter?
Now we know where coffee gets its bitterness, but do other factors matter when it comes to bitter coffee? Even after roasting is completed, the other steps required to brew coffee can also contribute to a bitter cup. These are:
1. Grind size
Finely ground coffee tends to become bitter. This is because the fine grind allows more compounds to be extracted from the beans into the cup. A coarser grind will slow down extraction and give a more acidic but less bitter cup.
2. Brewing method
The longer coffee is brewed, the more bitter it’ll be. This is simply because more compounds are extracted over a longer time and this increases the bitter taste in your cup.
3. Brewing temperature
The water temperature is very important when you brew. Like roasting, it provides heat that can cause further chemical changes. If you use water that’s boiling or just too hot, it can extract the lactones and phenylindanes much faster than it should.
When brewing, it’s all about balance. You need to select the correct grind size for the correct brewing method and carefully monitor your brewing process so that you avoid over- or under-extracting.
How Can I Avoid Bitter Coffee?
First, check what type of coffee you’re buying. Robusta is always more bitter, so stick to high-quality Arabica beans. Darker roasts have a harsher bitterness, so look for a light or medium roast.
If you don’t want bitter coffee, the most important thing to remember is not to over-extract. This means don’t brew for too long and pay attention to your grind size and chosen brewing method. Since a finer grind can over-extract quickly and end up way too bitter, it’s best to go for medium or coarse ground coffee.
Once you select your grind size, choose a brewing method that works well with that grind and that doesn’t require a long brewing time. Heat is also an important factor, so be careful with your water temperature. Cold brew is a great, low-effort way to make less bitter coffee. The lack of heat balances out the long brewing time to give you a smoother, sweeter brew.
Finally, bitterness is a subjective experience. Some people like very bitter coffee, some prefer just a hint of bitterness, and some just can’t stand any bitterness at all. Know what you like and work towards recreating that in every cup you brew. Don’t be afraid of bitterness- it doesn’t necessarily mean your coffee is bad, just that you need to experiment with it to find something that works.