Too much bitterness is probably the most common reason people don’t like coffee. Many will power through with milk and sugar to cover up the bitterness—after all, they still need their caffeine fix. But coffee brewing doesn’t have to be like this! Once you learn what makes coffee bitter, you also learn how to fix it by extracting less and finding coffee’s naturally sweet flavors.
So read on to learn the most common reasons for bitter coffee and how you can brew coffee that consistently tastes delicious.
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Bitter Coffee 101: What Makes It Bitter?
To understand what makes coffee bitter, you must first understand coffee extraction. Extraction is the process through which you dissolve flavor compounds from the coffee grounds into the hot water. All brewing requires at least some contact between the water and the coffee grounds, even if it is only for a short time, like espresso.
During an optimal extraction, water dissolves the perfect amount of flavor from the coffee grounds. This optimal amount of dissolved solids, known as TDS, is somewhere between 18-22% of total dissolved solids.
Extracting less than this will make your coffee taste sour and lack sweetness. And, extracting more than 22% will introduce too many bitter compounds into your brew. Even though brewing coffee can be a complicated science, fixing bitter coffee comes down to this two-way street:
So over-extracted coffee is one of the main culprits for what makes coffee bitter. For people who make French press coffee or pour-overs, you can decrease extraction by decreasing your brew time. But if you drink your brew from a coffee machine, you’ll have to mess around with dosing or grind size, which I’ll talk about later in the article.
And, for a more in-depth guide to coffee brewing and extraction, check out this article dedicated to the basics of brewing.
The 3 Reasons Why Your Coffee Is Bitter
When you zoom out, there are only two ingredients in coffee recipes: coffee beans and water. So it makes sense that bad beans or water can make a cup of coffee taste bitter.
These ingredients—bad beans and bad water—will be the first two explanations for what makes coffee bitter. After that, I’ll dive into the third cause of bitter coffee, bad brewing. As I already explained, over-extraction causes a bitter flavor that is empty and dry.
Bad Beans
Coffees that taste bad often have the simplest explanation of all: the main product—coffee—is bad. Bad coffee means the beans in your bag are low quality, stale, or improperly roasted. In this case, no amount of adjustments will fix the off-flavor compounds in your drink. Even the best barista in the world will still make a bitter brew.
Stale Coffee
The first reason your coffee might be stale is that it is way past its roasting date. Like any food, coffee beans age with time and the flavor compounds will become more and more muted.
Especially with specialty coffee, the desirable flavors in fresh coffee, like acidity and sweetness, will be replaced with a sour or bitter taste. Read more about how long coffee lasts to understand this process. Buying fresh coffee and storing the beans properly in an airtight container will prolong freshness for as long as possible. There’s really no good fix for stale coffee!
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The Problem with Pre-Ground Coffee
Another reason for stale coffee is that you bought a bag of ground coffee. When you have your coffee ground at the store, especially a fine grind like espresso, the aging process speeds up. Ground coffee has more surface area than whole beans, which means oxygen ages the coffee grounds quickly.
Depending on how fine your grind is, ground coffee can start tasting stale within minutes, even if it is fresh.
So besides buying higher-quality coffee with a recent roasting date, do yourself a favor and invest in a coffee grinder. Pre-ground coffee is a top reason behind what makes coffee bitter.
Bad Water
Water is the main ingredient in coffee, so, logically, bad-tasting water will result in a bad-tasting brew. Certain regions have particularly bad-tasting water, either because of added chemicals or mineral hardness. Proper brewing water requires some minerals, but too much can mess up the extraction process.
So drink a glass of your brewing water before you heat it to sample a taste. If the flavor of this water is off, then fixing your brewing water is the first step. You can try using filtered water or buying spring water from the supermarket. You might still have to make brewing adjustments after this, but to be scientific you should fix one variable at a time and see what effect it has on the coffee taste.
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Bad Brewing And Over-Extraction
Assuming that you’ve made sure the coffee beans are fresh and the water is decent, over-extraction is the only remaining cause of what makes coffee bitter. In a proper extraction, some amount of bitterness is desirable and gets balanced by other flavors like sweetness and sourness.
But when you over-extract coffee, you dissolve too many bitter compounds into the water. It creates an empty, bitter, and drying taste. Taking measures to extract less, which I’ll talk about in the next section, is your best bet for fixing bitter coffee.
And if you’re not sure exactly what is making your coffee taste bad, you can use this helpful coffee compass to analyze the flavor and figure out what adjustments to make.
Why Does My Coffee Taste Bitter All of a Sudden?
If you generally brew delicious coffee and your results are suddenly bitter, the two probable causes are bad water quality or grinder issues. Burr grinders are fantastic, but once the burrs lose sharpness (or if something inside breaks,) you can end up creating a lot of fines that over-extract and cause bitterness.
Another reason for sudden bitterness is that your brewing equipment is dirty. So, make sure everything is clean, especially the inside of machines. Lastly, if you did not properly seal your beans in an airtight container, bitterness may be coming from your beans quickly going stale.
The Science of Bitterness
The science of taste tells us that our taste buds can perceive 5 different categories of taste: sweet, sour, salty, bitter, and umami. The receptors on our tongue react to molecules and signal to our brain what flavors we are getting.
And while the old theory of a tongue map is no longer accurate, the back of your tongue actually has a higher sensitivity to bitter tastes.
When we eat food with a sour taste or bitter taste by itself, our receptors are overwhelmed. People generally perceive this experience as negative. Imagine having a drink of pure lime juice—you probably just made a face even thinking about it. But when you blend intense flavors at the right ratios, your brain will perceive this balance as pleasurable.
Is Bitterness Bad?
In all of this discussion about bitter coffee, it’s important to realize that bitterness isn’t inherently bad. And the same is true for a sour taste. Usually, the best-tasting foods and drinks combine a balance of flavors that harmonize like a musical chord.
A cocktail, for example, brings together sourness, sweetness, and bitterness (and the heat of the alcohol) to create a harmonious drink. In a cocktail like an Old Fashioned, you add dashes of bitters to balance the intense flavor compounds of the whiskey and the sugar.
And even though a bitter taste by itself can be offensive, it doesn’t have to be. Dark chocolate, for example, can get quite bitter and people still find it delicious.
The Roast
So for coffee, some amount of bitterness comes down to personal preference. And a lot of this preference depends on the coffee’s roast level. Just like you can cook a steak anywhere from rare to well done, you can roast green coffee from light to dark. A lighter roast is usually more subtle and floral, and the risk is usually making the coffee taste sour.
But for a dark roast, coffee oils from deep inside the bean are driven out by the heat of roasting. You’ve probably seen the oily texture of a dark roast. These oils contribute to the bitterness of coffee. But for those who prefer a dark roast, this bitterness is a desirable taste. It especially works with milk and sugar.
In the negative sense, careless dark roasting of coffee is a common cause of bitter coffee. Many coffee roasters will roast large quantities of beans at a higher temperature. This burns the beans and kills any of the subtle flavors.
Specialty coffee roasters, however, roast in smaller batches. They take much more care with finding the perfect roast level to avoid negative flavor compounds.
Fix Bitter Coffee by Extracting Less
Assuming that you’re brewing with a medium or light roast (or a proper dark roasted coffee), let’s examine the brewing adjustments you can make to fix bitter coffee by extracting less.
The relationship between brewing ratio and extraction is complicated. Feel free to experiment with this ratio (especially if you don’t have a grinder), but for fixing bitter coffee, the following three adjustments will decrease your extraction:
- Use a coarser grind.
- Make your brew time shorter.
- Decrease your water temperature (read more about coffee brewing temperature.)
A coarser grind means less surface area from the coffee grounds is interacting with the water. Extraction will decrease and bitter flavors should lessen as you make the grind size bigger. And decreasing brew time results in a lower extraction because the water has less time to interact with the ground coffee. Lastly, a lower water temperature means the water has less energy to interact with the coffee grounds.
Adjust One Variable at a Time
Taking all of these measures at the same time will lower your extraction even more, but adjusting one variable at a time is more scientific. If you don’t have a coffee grinder and you can’t control the brew time or temperature on your coffee machine, your best bet to fix bitter coffee is to use more coffee.
A higher dose will make a stronger cup. But with more coffee around, the extraction percentage should decrease.
How to Make Coffee Less Bitter Once You Brew It
Obviously, the best bitter coffee fix is to prevent the bitter flavors from appearing in the first place. This would involve dumping out the badly brewed coffee you just made and starting over to get a better extraction.
But if you want to salvage what you have and make it more palatable, you’re not completely out of luck. There are a few tricks for how to make a coffee taste less bitter. Let’s check them out!
Dilute with Hot Water
One way to mask bitterness is to dilute the strength of the bitter coffee with some additional hot water. To be clear, this method will not get rid of the bitter compounds—they will have less strength but you will still taste them.
Anything that is more concentrated has a stronger taste. So adding some additional hot water will weaken the coffee and help cover up the bitterness. This method is good for people who generally like the flavor of coffee and prefer not to add milk and sugar.
Add Milk And Sugar
Milk and sugar complement the flavor of correctly brewed coffee, so it’s no surprise that these two additions can fix bitter coffee. When coffee tastes bitter, it means there is a lack of balance between the different flavor compounds.
So you can balance a bitter brew with some sweetness. If your coffee only has a subtly bitter flavor, the natural sweetness from milk can be enough to balance the bitter compounds. But if the bitter flavors are truly overpowering, you might need the help of sugar. Start with a small amount and keep adding until the bitterness is less offensive.
Frequent Questions About Bitter Coffee
Before wrapping up this article, let’s give a few simple answers to some of the most common questions about bitter coffee and how to fix it.
Why is my coffee bitter with darker roasts?
Darker roasts tend to extract more easily than lighter roasts, so my recommendation is to use lower water temperature when brewing these types of beans.
What takes the bitterness out of coffee?
Besides brewing better next time, you can improve the taste of bitter coffee by diluting it with hot water or by adding strong flavors like milk, cream, and sugar to dilute the bitter compounds.
Which type of coffee is bitter?
Of the two main varieties of coffee that people consume (arabica and robusta), robusta beans have far more naturally occurring bitter compounds. Also, darker roasts will tend to produce more bitter compounds.
Final Thoughts
Bitter coffee, or any bad-tasting coffee, is often out of your control. If you have a bad bag of beans or your water chemistry is off, there’s not much you can do. But assuming you have high-quality beans (like a bag of specialty coffee) and good water, fixing bitter coffee is all about extraction and brewing.
And now that you know what makes coffee bitter, you know how to adjust your extraction to get a better-tasting cup. And if you retain some flexibility with your coffee recipes, you can tweak them anytime to bring out a different balance of flavors.
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