Coffee Taste Sour – Why And How To Fix It

Ever tasted coffee and realize that your coffee taste sour?

Or have you ever ordered a cup of americano from a coffee shop and let it sit for far too long? As you sip the icy cold americano and you suddenly feel that jolt on your tongue because of how sour it is.

Being a barista, home brewer, and an avid coffee consumer, I have had my fair share of sour coffee myself too.

Now, before jumping to conclusions saying sour coffee is bad, there are several explanations for it. Not discounting the fact that something might have gone wrong in the coffee preparation process. 

So, in this post, let’s look at a few possibilities of why your coffee tastes sour.

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At a glance: Coffee Taste Sour – Why And How to Fix It

Misconception Between Acidity and Sour Flavor

Before diving into the reasons why coffee taste sour. We need to clarify the differences between acidity and sourness. A pretty common misconception.

So what is the difference between acidity and sourness?

Acidity 

Acidity defines a huge part of the flavor of coffee more than we know it. In fact, there is a huge array of flavor notes in the Coffee Taster’s Flavor Wheel that highlights acids from fruits.

So, where does the acid come from? 

First off, the coffee bean by itself has naturally occurring acids. Before the coffee bean reaches the café store, it passes through a series of processing stages and then roasting. Without diving into the details, the processing stages and roasting changes the chemical composition in the coffee bean which directly affects its final flavor.

Naturally, acids are described to be sour. So, coffee is sour if you put it that way. 

But there are distinct differences between a pleasant acidic taste and an unpleasant sourness. As a simple analogy, think sweet cherry against a lemon. 

If a certain coffee bean was tagged to have a flavor profile of sweet cherry, it is highly likely that the acid composition in the coffee bean matches the one of a sweet cherry!

Sourness

The sourness you experience when you consume coffee is when the acidity levels are too high and becomes overwhelming for your taste buds. 

How does this happen? 

Say for example, an espresso shot which typically takes 30 seconds for full balanced extraction. During the first 15 seconds, the acids and aromatic compounds were the first to be extracted. Followed by sweet syrupy compounds and finally the bitter parts. 

Too much of each will result in an unbalanced cup of coffee. And in this case, under extraction of coffee leaves the sweet and bitter compounds in the coffee grounds while the acids are all in your cup; leaving your espresso too sour to consume.

The key here is balance. 

Common Acids In Coffee Beans

Now that we know that with the right amount of acids in your coffee, the drinking experience is pretty pleasant. Break the balance and you will end up with your coffee too sour. 

Let’s look at some of the most commonly found naturally occurring acids in coffee beans.

Citric Acid: 

As the name suggests, this type of acid is very commonly found in citrus fruits! Tasting coffees with this acid makes you think of fruits such as grapefruits, tangerines, oranges, lemons, and nectarines.

Malic Acid: 

For this acid, you can commonly find them associated with the clear crispiness of green apples or stone fruits such as peaches and cherries. With the malic acid present, one would expect a sharp zing when tasting coffee with the malic acid present.

Acetic Acid: 

Not a fruit-related one for this acid but it’s basically the main compound that makes up vinegar! Yes, you read that right. Unlike citric and malic acids, acetic acid develops during the processing and roasting phases. 

Although the thought of having vinegar in coffee does sound unpleasant, hints of such acids give the coffee a different layer of complexity. When done right, it could be delicious!

Tartaric Acid: 

Closely associated with the flavors of grapes. Tartaric acid features that dry and tart flavor that is found in wine too.

Phosphoric Acid: 

The phosphoric acid brings that sparkling tangy and slightly sweet flavor profile to the coffee experience. One could associate the flavor with a blackberry.

Quinic Acid: 

Dubbed as the black sheep of acids to be present in coffee; Quinic acid develops during the roasting process where chlorogenic acid is broken down and is the reason why it is evident in darker roasted coffee. Without a doubt, it is the main contributor to the bitter and astringent flavor in coffee. It brings unpleasant acidity and is often the main culprit for causing stomach issues.

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Knowing the above, most of the acids can be related to fruits. But we would have naturally categorized these fruity flavors as sour when really, we are just not simply used to it. This is particularly true when the final cup of coffee contains high quantities of the acids described above. However, with the right proportions of different acids, coffee can be a pleasant experience with a combination of complex layers of flavors.

In the case where the final brewed coffee is astringent with unpleasant sourness, it may be due to the following reasons which I’ll talk about in the next section.

Reasons Why Your Coffee Taste Sour

1. Grind Size Is Too Coarse

You would also expect coffee to lean towards the sour side when the coffee grind size is too coarse. The main reason to grind coffee is to break down a whole coffee bean into smaller pieces for better extraction. 

When the coffee grind size is too coarse, the water does not have enough time to grab all the flavor compounds from the coffee ground. This would result in a very unbalanced cup of coffee; highly acidic and not enough body.

On the flip side, grinding the coffee bean finer exposes more of the coffee ground surface area to the passing water. This allows the better rate of extraction of flavor compounds from the coffee bean resulting in a more balanced and rounder body cup of coffee.

However, this does not mean one should set the grinder to the finest size. Coffee grounds which are too fine will result in a bed which is too densely packed in which water could hardly pass through. It is important to find the balance here!

2. Under Extraction

As described above, the key to getting a good cup of coffee is a balanced extraction of compounds from the coffee beans. In a roasted coffee bean, about 28% of its mass is soluble in water. 

Under extraction is when there is insufficient water to grab these compounds from the coffee bean grounds and a lot of the good stuff is left in the coffee grounds. The compounds present in the brewed coffee are unbalanced and you can expect your coffee to have that unpleasant sourness and a disappointing finish.

Of course, too much water on the other hand will result in an over extracted coffee which will taste bitter and flat.

In fact, caffeine which exhibits bitter flavors is one of the last compounds to be extracted from coffee. Again find the balance!

3. Over Roasting

During the roasting phase, the heat introduced to the coffee beans will cause chlorogenic acid to be broken down into quinic acid and caffeine. As we’ve discussed above, both of these chemical compounds are bitter and unpleasant. 

However, by roasting coffee beans, Maillard reaction occurs where sugars and proteins chemically react and produce a huge variety of beautiful flavor compounds; yes even the unpleasant ones like onion. It is the roaster’s responsibility here to find the balance!

4. Beans Are Too Fresh

Yes, you read that right, coffee beans being too fresh can also lead to sour coffee extraction! 

When brewing with beans which are too fresh, the carbon dioxide gas particles will reduce the extraction efficiency of the water. 

During the roasting process, heat causes the gas molecules in the coffee bean to escape as the coffee bean surface cracks. In this case, it is carbon dioxide. Notice when you brew pour over coffee, you would see bubbles forming as the hot water comes in contact with the coffee grounds. 

So when your coffee beans are out fresh from the roaster, there are still trapped gasses within the coffee bean which will disrupt the contact period between water and the coffee grounds. Hence, resulting in a poorly extracted cup of coffee.

This is why your roasters may advise you to “rest” the beans for a week or two before consumption. 

5. Type of Coffee Beans

In my previous post on coffee varietals, you learn that the coffee family is vast and each species has distinctive flavors. Therefore, it is not surprising to find certain kinds of coffees with high acid content but do not mistake them for sour coffee beans.

For example, coffees from Ethiopia are well known to have incredible fruity notes. Personally, my first encounter with a strawberry-tasting note coffee was an Ethiopian coffee!

On the other hand, you will find Columbian coffee having the classical coffee tasting notes; nutty, chocolaty with a caramel finish. 

How To Fix Sour Coffee?

So what do you need to do when your espresso tastes sour?

Remember, you now know that we know that we should seek acidity and not sourness, and there are ways to try to minimize the unpleasant sour taste in coffee. 

Here are some steps you could take to reduce the unpleasant coffee acidity.

1. Grind Finer

As you grind the coffee beans finer, you expose more surface area for water to extract the beautiful flavors from the coffee grounds. Adjust the coffee grind size bit by bit until you hit the sweet spot!

2. Increase Brew Time Or Extraction Time

For an espresso machine, you can allow a longer extraction time which enhances the extraction of compounds and provides sweetness and body if your espresso tastes sour. 

For brewing methods such as Aeropress and French Press, you can allow your coffee grounds to steep slightly longer. Taste and change the brewing/extraction time as you see fit!

3. Coffee To Water Ratio

The coffee to water ratio is basically your recipe.

Having too much coffee and insufficient water will result in under extraction; naturally, your taste bud will question why your coffee tastes sour. On the flip side, having too much water will over-extract your coffee and result in a fairly bitter cup.

A good practice is to note down your brew ratio every time you brew yourself a coffee. Taste your coffee and make a mental note on what to change in your next brew. 

4. Water Temperature

The hotter the water, the more energy it carries. Hence, hotter water will result in a stronger extraction which may result in over-extraction and vice versa for cooler water. Generally, one would start with a water temperature of 93^oC (200^oF) as a benchmark and adjust from there.

But cold brew uses room temperature water! What do I do when my cold brew tastes sour?

In this case, since the temperature is your limiting factor, simply increase your extraction time! 

FAQ On Sour Coffee

How Do You Get Rid Of Sour Taste In Coffee?

To get rid of sour taste in coffee, simply make your grind size finer, make your water hotter, brew for longer, or use more water in your recipe. The sour taste is usually due to under extraction. The flavor compounds which contribute to sweetness and body are extracted later during the process. 

Can You Drink Sour Coffee?

Can you drink sour coffee? Of course! It is a personal preference to choose to drink a cup of sour coffee. However, coffee sourness is often confused with acidity. With the right amount of acidity, it is pleasant on the palate just like berries. If there isn’t enough balance, the acidity may be overwhelming and hence perceived as sour coffee. 

Why Does Cold Coffee Taste Sour?

The main reason why cold coffee tastes sour is due to the extraction temperature. When the temperature is too low, these compounds and flavors aren’t fully extracted. The other flavor compounds which bring sweet and bold flavors are not being extracted to balance out the acidic flavor compounds of the coffee.

Coffee Taste Sour: Conclusion

If your coffee taste sour, I hope this blog post has helped you understand a thing or two about sour coffee and how to fix them. Troubleshooting the reasons why your coffee tastes sour can be a little tricky as there are so many variables to tweak. 

Being a barista before and a home brewer, I understand the frustration of a brewed coffee sour aftertaste wrong and seeing your coffee beans go to waste. 

The trick here is to change one parameter at a time while keeping all other variables fixed. For example, do not fiddle with the grind size and also change the brew ratio at the same time when troubleshooting. 

All the best in brewing the sweetest cup possible!