Why Does My Coffee Taste Sour? (And How to Fix It)

Have you ever used freshly roasted coffee beans that smell delicious, only to end up with an unpleasantly sour cup? If so, the issue is probably rooted somewhere in the brewing method rather than the beans themselves.

But, before you start tweaking your setup, it helps to understand what sourness means in coffee and all the different causes. Then you’ll know what went wrong and how to fix it. So, grab your favorite mug and join us as we explore how to avoid sourness and brew a deliciously balanced cup. 

What Does Sour Coffee Actually Mean?

Sour coffee is different from the natural acidity present in all coffee. Coffee acidity should have pleasant flavors like hints of lemon, green apples, or stone fruits, which are balanced out by the natural sugars, oils, and subtle bitter compounds also present in coffee.

Actual sourness, however, is a sharp, puckering sensation in your mouth that lacks sweetness or depth. That’s usually a sign that something went wrong, either in storage, home roasting, or, more likely, during brewing. 

The Most Common Reason Coffee Tastes Sour: Under-Extraction

The most common reason coffee tastes sour is underextraction. This happens because brewing pulls different flavors out in a fairly standard order. Bright acidic compounds come out first, followed by sweetness and body, and finally bitter, roast-forward flavor notes last.

Underextraction means the coffee hasn’t had time to pull out enough of those sweet and roast-forward flavor notes, resulting in brews that taste sour from unbalanced acidity. 

The Primary Causes of Sour Coffee

The Grind Is Too Coarse

With most brewing methods, if your grind is too coarse, the water may drip through the filter too fast and not have enough time to extract the full flavor, leading to underextraction and sour tastes.  

The Water Temperature Is Too Low

Another common cause of underextraction is using water that has cooled below 195°F. Water that’s not warm enough reduces extraction efficiency because it lacks the energy it needs to extract all the flavors as quickly as required.

The Brew Time Was Too Short

Of course, coffee needs time to extract all those delicious sweet and roast-forward flavors, so if you simply cut the brew time short, either by plunging too quickly on the French Press or AeroPress or pouring too fast in a pour-over dripper, it may not have enough time to extract efficiently. 

The Coffee-to-Water Ratio Is Off

Your coffee-to-water ratio is also important. If you don’t use enough coffee for a balanced brew, it can cause your coffee to taste weak and thin, which may make the acidity stand out, giving it an unbalanced sourness.  

The Coffee Is Stored Poorly 

Usually improperly stored coffee goes stale and tastes flat. However, if it’s exposed to water or high humidity, it could result in spoilage or mold, which may produce sharp, sour flavors. If you suspect spoilage, toss those beans and store your next batch in a sealed, airtight container. 

The Coffee Is Under-Roasted

Sometimes new home roasters trying to achieve a very light roast may not roast it long enough. If your beans are stopped roasting before first crack while still yellow instead of the light brown you expect with a light roast, it may also produce sour and grassy tastes. 

The Equipment Isn't Clean

Finally, if you don’t clean your brew system after use, it can develop musty, stale, or sometimes sour flavors from microbial growth. Be sure to properly clean and dry your brew equipment between uses according to the manufacturer’s instructions. 

Sour Coffee by Brew Method: Quick Fixes

If you get sour coffee and you know it’s not from poorly stored beans, under-roasting, or dirty equipment, try these quick fixes, which may depend on your coffee brewing method.

Tip: Make small adjustments to avoid pushing it into overextracted, bitter flavors, and only change one variable at a time so you know which fix worked.  

Is It the Coffee, Not the Brew?

With thousands of taste buds on the human tongue, which vary enormously from one person to the next, taste is very personal, so naturally, what tastes great to one person might not taste great to another.

For instance, while some people thoroughly enjoy light roasts, they inherently have more bright, pleasant acidity than other roasts. But if you’re coming from dark, roast-forward cups, that lively acidity can be taken for sourness simply because that’s not what you’re used to.

However, if you try a freshly roasted, correctly brewed light roast and find the natural fruity acidity unpleasant, it also might just not be your thing. In that case, you may prefer a medium roast with a balance of natural acidity, flavors from the origin, and roast-forward flavor characteristics.

For example, our certified organic, Fair Trade, shade-grown Mexican Chiapas from our farmer partners at the Cooperativa de Producción Tzeltal-Tzotzil is a well-balanced medium roast with notes of brown sugar and cinnamon that might be more to your liking.

Frequently Asked Questions

Why Does Coffee Leave a Sour Taste in My Mouth?

All coffee is slightly acidic, but that acidity should be pleasant and fruity, like mild lemon or stone fruit. But if your coffee leaves an unpleasant, sour taste, it’s likely underextracted. This can happen from not brewing it long enough, using too coarse of a grind, or water that isn’t hot enough. 

What’s the Difference Between Acidic and Sour Coffee?

All coffee is naturally slightly acidic, and light roasts in particular have more pronounced acidic flavors than dark roasts, but their acidity is bright, fruity, and pleasant. Sour coffee is different; it’s usually caused by under-extraction and it leaves an unpleasant puckering sensation in your mouth. 

Is It Okay to Drink Sour Coffee?

It depends. If the coffee is sour because the beans are old and moist, toss it since it might be moldy. However, if properly stored coffee tastes sour, it’s most likely underextracted, which is still safe to drink; next time, try brewing longer, grinding finer, or ensuring your water is 205°F for a more balanced extraction. 

Better Beans Make Every Extraction Worth the Effort

All the best brewing techniques rely on quality beans to produce a tasty cup. Starting with freshly roasted, certified organic, Fair Trade coffees sourced through long-term partnerships with farmer cooperatives will help you find the perfect roast or origin for your brewing method.