What Makes Coffee Bitter? (There are 8 Reasons Why)


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Coffee is absolutely associated with bitterness. Whether you like it or not, it’s part of the coffee’s variety of flavors. Coffee is a complex mixture of different organic compounds found in green coffee bean extract. This extract tends to produce a complex overall flavor that affects the human response to coffee or caffeine once tasted. 

But what makes coffee taste bitter?

The bitterness we’re talking about is more of a dominant taste that overpowers the sugars and aromas. We often taste it in our cup simply because of having bad quality beans or having a bad brewing technique. Technically, low-quality coffee such as Robusta species, low-grade beans, and even super dark roast beans just tastes bitter no matter what.

In this article, we’ll further discuss the factors that create or contribute to the perception of bitterness. Understanding it means avoiding the unnecessary things that we might still be doing in making the perfect cup of coffee every morning.

tasting bitter coffee

1. Over-Extraction

coffee extraction

The main reason why your coffee tastes bitter is because of over-extraction. It means that you extract a bunch of bitter chemicals from your coffee grounds during the brewing process.

So, if your coffee influences perceived bitterness or even bad, it is because you didn’t extract the right amount of flavor from it. Most of the time, probably, bad-tasting coffee is the result of improper extraction. You can read our guide on coffee brewing control chart for more information.

Moving on, the following factors may also contribute to the bitterness of your coffee. Let’s take a look at the list and find out more about what’s causing the bitterness in it.

2. Over-Roasted Coffee Beans

If you take a deeper look into the coffee roasting process, you will see the importance of it to the brews you enjoy every morning. You will also see the disaster it may create if not paying attention to the proper roasting of coffee beans.

Sure, the bitterness in your coffee is one of its distinctive flavor characteristics, which is developed during this process.  

roasted coffee beans

But roasting coffee beans is considered as an art and even science, that making even a single mistake along the way could ruin a batch of coffee beans quite easily.

A common mistake for most households and new to roasting individuals is that they over-roast their beans because they wanted to have a strong-tasting coffee. 

Well, that’s not the proper way to make a strong coffee, and doing that will only make the cup taste awful. Over roasting your coffee beans leads to over developing a bunch of bitter chemicals.

Why Does Roasting Increases Bitterness?

Bitterness is associated with the roast profile and also one of the key factors that differentiate light roast from dark roast coffee. Lighter Roasts tend to have lesser bitter compounds compared to dark roasts because it was roasted in a short amount of time.

So, knowing that dark roast is more bitter, the question now is, “what makes these compounds increase when the roasting continues?

From an article published in 2007, Thomas Hofmann and his research associate Oliver Frank found that two groups of components were significant contributors and are responsible for the coffee bitterness – chlorogenic acid lactones and multiply hydroxylated phenylindanes – which the amount of these components in your coffee is linked to the roast profile.

That is, according to Dr. Hofmann, if the coffee is in light- to medium-roast, it will have more of the acid lactones, which create a “pleasant, coffee-like bitter taste quality.” On the other hand, if roasting continues, resulting in over-roasted coffee, it will have more phenylindanes, which the one responsible for a “lingering, harsh type of bitter sensation,” 

So, it means the more you roast your coffee, the more amount of phenylindanes your coffee may acquire which creates the perception of bitterness. 

Dr. Hofmann further said in the article that the final roasting temperature influences not only the quality and quantity of aroma compounds that give coffee its enticing character but also the correct ratio between bitter and acid flavor.

3. Using A Wrong Grind Size

ground coffee beans

The size of the grind is essential to the taste of your coffee as it will greatly affect the coffee you brew. Using a wrong grind size to your preferred brewing method may lead to a coffee that has an extra taste of bitterness instead of good and smoothy flavor.

As mentioned before, over-extraction is the main reason why your coffee tastes bitter. And over-extraction happens most of the time because the beans are ground into an extremely fine powder. This grind consistency has more surface area for water to extract too much flavor faster. For more details, check our guide on how to grind your coffee beans properly.

4. Letting Your Coffee Steep For Too Long

French press coffee brewing

Normally, the best way brew a great-tasting cup is by steeping the ground coffee in hot water. However, while you can let the tea steep for a little longer as it doesn’t directly affect its taste, it may not be effective when it comes to coffee. It may lead to over or under-extraction as time is crucial to brewing.

Letting your coffee steep for too long, especially if the water is too hot, leads to an over-infused cup of bitter-tasting perception. That is because you will dissolve more bitter flavors from the grounds in that amount of time.

Therefore, it’s recommended that once your coffee is done, always transfer it immediately to a thermos to keep it hot.

And when it comes making French press coffee, avoid leaving the coffee in the French press after you have pushed the plunger down. Don’t even wait for too long to press down the filter to avoid over-brewing the grounds.

5. The Water Is Too Hot

Moving on, the water temperature affects the way your coffee taste. The hotter your water is, the more you over-extracts the flavors from the grounds, including the bitter compounds. 

boiling of water

A common mistake for most households is letting the coffee boil for too long, thinking that it is the right way to extract all the good flavors from it.

Well, remember that coffee is a complex mixture of many chemicals, including the chemicals that are responsible for its bitterness. So, if you continue to apply heat to the coffee, the coffee may get over-cooked. That way, you can possibly ruin the good stuffs, and there’s a tendency to burn the coffee or even may become acidic within a minute. 

  • According to Dr. Hofmann, which is mentioned before, the longer you keep your coffee hot, the more you degrade the aroma molecules, and in particular, those exhibiting the pleasant sulfury and roasty smell.

He further said that the acidity increases too because the lactones are hydrolyzed to form free acids, which means fresh coffee has a pH between 5.0 and 5.4; that can drop to 4.6 if the coffee is kept hot for two or three hours, increasing sourness and also influencing dominant taste of bitterness.

Simply put, if you continue to apply heat to your coffee, it will begin to lose good flavors including the smell, leaving only the taste of sourness and bitterness.

6. Beans Are Mixture Of Ripe And Unripe Cherries

brewed coffee

Let’s continue with the quality of the coffee bean you used.

Whatever your roasting and grinding techniques are, sometimes the bean itself is one of the reasons why your coffee tastes bitter. 

  • According to the study conducted by the Food and Agriculture Organization, it shows that the use of immature or unripe cherries in the coffee production to the processing method is associated with poor quality coffee. 

It means that the unripe green cherries that are mixed with the others will make the coffee taste more bitter in the final cup. Coffee made from unripe cherries has undesirable taste characteristics. That is because the beans from such (unripe) cherries are prone to blackening during the drying process.

7. Defective Beans Are Used

coffee beans that are poorly roasted

Speaking of defects, a defective bean can actually change the taste of coffee in a cup. Possible effects are the moldy/off-flavor and the loss of all of its aromatic and taste characteristics, and even sometimes result in a bitter taste.

Also, the Specialty Coffee Association of America said that improper harvesting of coffee cherries influences potential defects to its bean, leading to a taste that is more of the structural material of the fruit rather than the perfectly developed sugars and acids that people love.

8. Coffee Beans Aren’t Fresh

stale roasted coffee beans

One of the reasons why your coffee tastes bitter is because you brew coffee grounds stored and forgotten somewhere for a long time. And maybe worst if was stored improperly. 

Sometimes coffee beans stay fresh for several months or even longer once roasted, but once ground, it may not stay fresh for that amount of time.

That’s why it’s always best to consume it within two weeks after grinding, otherwise, there’s a chance that your coffee may taste bad as they begin to lose essential and aromatic flavor in just a matter of time. With its flavor to change dramatically within a few minutes, the coffee may continue to deteriorate until it is consumed.

Furthermore, the exposure of the coffee oils to air at room temperature leads to fast oxidation which can cause unpleasant flavor and smell. Usually, these rancid flavors come from chemical change or reaction within the coffees. It means that letting the coffee oils to continue in releasing gases and oxidation will definitely affect the taste. That is why it’s important to store your coffee beans properly.

Is Bitter Coffee Bad for You?

When it comes to the taste, a gentle kind of bitterness is what we’re looking for. Wrapped with fruity and floral flavor. Indeed, a great cup of coffee is simply made with the right balance of acidity, sweetness, and of course, bitterness.

Afterall, bitterness in coffee doesn’t have to be a bad thing.

  • Researchers expect that people who are more sensitive to the bitter taste of caffeine would drink less coffee, but it turns out that many people avidly consume drinks or beverages that contain caffeine, despite its taste.

So, why this thing happens? I find also that coffee is super addictive regardless of its bitterness.

A certain study shows that those people who are sensitive to the bitter taste of caffeine actually drink more of it. That’s why, it makes sense that we “coffee lovers” still enjoy our brewed coffee and are used to its perception.

Sometimes coffee is all about personal taste and the taste of it can vary substantially across individuals. It means that some people are supersensitive to coffee’s bitter taste and some are not.

Ways to Fix the Problem of Bitterness

Getting Started with Beans

To avoid bitterness in your coffee, choose the right roast that suits your needs.

If you’re fun of roasting your own coffee beans at home, be careful not to over-roast or burn them. We’ve written a guide on the stages of roasting if you want to learn the coffee roasting process.

But if you’re buying from various places, I recommend you check the quality and freshness of roasted coffee beans. There are many places out there, but the most popular choices are through local roasters, subscription services, and legitimate online brands. Let’s take a look where to buy coffee:

  • Local Specialty Roasters – If there’s a local roaster nearby, then that is the best place to outsource freshly roasted beans. You can probably get high-quality and freshly roasted beans in a minute. In the end, you can you avoid bitter coffee because roasters can assist you and give you enough idea on the type of roast to choose.
  • Subscription Services – You can sign up on subscription services to receive freshly-roasted coffee on a regular basis. Bean Box is an online coffee subscription that curates a variety of coffee from world’s best artisan roasters. And you can enjoy every cup of joe at peak flavor as they deliver your coffee fresh.
  • Volcanica Coffee – One of the great places to buy freshly roasted bean is at Volcanica Coffee. You can’t go wrong with them as their experienced roast masters understand the nuances and delicacies involved in roasting, avoiding the lingering taste of bitterness in your cup. They roast coffee every week in their state-of-the-art facility in Atlanta to regularly produce fresh coffees.

Honestly, there are probably hundreds of choices out there. These are only the ones I’m familiar with, and you can explore each to find the best place. In the end, what matters is you know how a certain roast profile is associated with bitterness. 

Choosing the Right Grind Size

While it’s recommended grinding your beans at home, it’s still important to know what grind size is suited to each brewing method.

For example, coarse grind size is best for French press, while fine grind size is best for espresso and Turkish coffee. Check out our recent article on how to grind your coffee beans to find the preferable recipe between your grind and brew method.

It’s all down to grinder – A great grinder will help achieve the consistency of ground particles. Use a burr grinder that provides a perfect and consistent result. Here’s a list of the best coffee grinders to pick from.

  • I think even an entry-level grinder, such as the Baratza Encore can help you avoid bitter coffee, as long as you’re getting high precision and control over the coarseness of your grounds.
  • A manual grinder has also a more precise and consistent result. I recommend the JavaPresse Manual Coffee Grinder to get started with. It’s a little bit cheaper, but offers a superior grind quality.

After choosing the coffee grinder that consistently grinds your beans to the right size, explore and adjust the size to fit the method of your brew.

If your coffee tastes sour, your grind size is too coarse, then try to grind your beans a little finer. And if it tastes bitter, your grind size has the opposite issue, so, try to go coarser.

Final Thoughts

As mentioned before, bitterness in coffee is not always a bad thing. In fact, we all need the right amount of bitterness to ensure that the complexity and balanced flavor are obtained in every cup of coffee we consumed.

However, if extra bitterness is what you always get in your coffee, remember the key factors that affect its taste – the type of beans used, how it is roasted, the amount of grind, and how it’s brewed. This time, if you can figure out exactly why your coffee is tasting bad, you can avoid those mistakes and able to make a great-tasting cup of coffee with just the right level of bitterness.

Like this Article? You Might to Read: Why Does My Coffee Tastes Watery? (6 Tips to Fix it)