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Coffee Basics

Why Your Coffee Tastes Sour & 6 Simple Ways to Fix It

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Half of a dried lemon sitting in a pile of coffee beans

If you’ve ever taken a sip of coffee and your mouth immediately puckered like you were drinking freshly squeezed lemonade, you know firsthand how unpleasant a sour cup of coffee can actually be.

While brewing a great cup of coffee isn’t rocket science, it’s also not as easy as just pressing a button (even when using a machine that only requires pressing a button).

In this article, we discuss the reasons why coffee tastes sour and provide some simple solutions for fixing it.

Why Your Coffee Tastes Sour

It’s important to note that acidity and sourness are not the same thing. 

Coffee is naturally acidic and contains a variety of different acids. These acids are essential and highly desirable, as they’re what gives coffee its bright, crisp, and lively flavors.

On the other hand, sourness occurs when there’s an imbalance of acidity. Think of biting into a lemon or the taste of vinegar. Too much can overwhelm your cup and make it undrinkable.

There are three main reasons why your coffee tastes sour:

1. Under-Extraction

During the brewing process, certain compounds are extracted from the coffee grounds in a specific order. 

The fats and acids are extracted first and are what give the coffee its sour taste. Next are the sugars, which provide sweetness and balance to the overall flavor. Last to be extracted are the plant fibers, contributing the various bitter elements to the final brew.

If the brewing process happens too quickly, not enough of the sugars make it into the cup, resulting in an under-extracted, sour-tasting coffee.

2. Stale or Ultra-Fresh Beans

If stored properly, an opened bag of coffee beans will stay fresh for up to 3 weeks. After that point, they start to lose their flavor and can taste stale, flat, and even slightly sour.

Conversely, beans that are too fresh, just off the roaster, can also have a strong sour flavor. This is caused by the excessive build-up of carbon dioxide during roasting and requires giving the beans time to degas (rest) before brewing.

3. Under Roasted Beans

When green coffee beans are roasted, they undergo something known as the Maillard reaction. This process creates a chemical reaction between amino acids and reducing sugars within the beans, contributing to their color and flavor development.

If the beans aren’t roasted long enough, the sugars aren’t able to fully develop. This creates a significant imbalance of fats and acids in your final brew, producing a grassy, sour taste.

6 Simple Ways to Fix Sour Coffee

The good news is if your coffee tastes sour, there are some simple things you can do to fix it.

IMPORTANT NOTE: When implementing any of the following suggestions, it’s critical you try them individually and make small, incremental changes. Doing too much at once can lead to the opposite problem and leave you with a harsh, bitter cup of coffee.

1. Use a Finer Grind

Grind size plays an important role when it comes to extraction.

For example, the coarser the grind, the less surface area the water has to interact with during the brewing process. This limits the amount of compounds the water is able to pull from the grounds and can result in an under-extracted cup of coffee that tastes sour or flat.

HOW TO FIX: Start with the grind size recommendations for your chosen brewing method. If the sour taste persists, try a slightly finer grind. Continue to make minor adjustments until you’ve achieved the desired flavor.

2. Increase Your Brew Time

Brew time refers to the amount of time water is in contact with the coffee grounds. The shorter the brew time, the greater the possibility of ending up with an under-extracted and sour-tasting coffee.

With drip methods such as pour-over, Chemex, or auto-drip, your brew time is heavily influenced by your grind size. The coarser the grind, the faster the water will pass through the grounds, and vice versa.

For methods that use some degree of immersion, like the French press and AeroPress, your brew time will be determined by when the grounds are separated from the final brew.

HOW TO FIX: Start by following the recommended brew time for your chosen brewing method. If your coffee still tastes sour, increase your brew time in 15-second increments.

3. Add More Water

When brewing, the amount of coffee grounds used in relation to water is known as the coffee-to-water or bew ratio. This ratio is another essential factor in achieving the right balance between over and under-extraction.

The lower the ratio, the less water that comes in contact with the grounds, thus reducing the number of sugars and sweeter compounds that get extracted.

HOW TO FIX: A good starting point is the “Golden Ratio,” which uses 1 gram of coffee for every 18 grams of water. If your coffee still tastes sour, try adjusting the ratio higher (use more water).

4. Raise the Water Temperature

The optimal brewing temperature for coffee is between 195°F and 205°F (90°C and 96°C). Water that’s cooler than this won’t dissolve all of the tasty and flavorful compounds, leaving your coffee unbalanced and under-extracted.

HOW TO FIX: When brewing a lighter roast, aim for the higher end of the recommended range. Because these beans are denser, they require more heat for proper extraction. For darker roasts, stay towards the lower end to help minimize bitterness.

If you don’t own a thermometer, an easy hack is to bring the water to a boil and then let it cool for approximately 30 seconds to a minute when brewing a light roast and two to three minutes for dark roasts.

5. Pay Attention to Freshness

As mentioned earlier, sour coffee can be caused by stale or old beans as well as beans that are just off the roaster and aren’t quite ready to be brewed yet.

HOW TO FIX: Pay attention to the roast date stamped on the bag of coffee and try to use it within 1-4 weeks of that date to take advantage of peak freshness.

As a side note, most coffee sold in grocery stores won’t have a roast date on the packaging and will already be past its peak freshness by the time it’s placed on the shelves. 

This is why we recommend specialty coffee shops or buying from local and online roasters, as they’re much more likely to offer high-quality, freshly roasted coffee beans.

6. Try a Darker Roast

While sourness isn’t directly related to a coffee’s roast level, lighter roasts tend to be more acidic. 

If your palate is more sensitive to acidity, lighter-roasted coffee could come off as sour-tasting, depending on how it’s brewed.

HOW TO FIX: If your coffee tastes overly sour, there’s a good chance you may be brewing a much lighter roast than you think. If so, switch it up and give a medium or dark roast a try.

However, it’s important to note that the coffee industry lacks standardization when it comes to labeling roast levels. What one roaster calls a medium roast, another might classify as light. This is why it’s important to experiment with different coffees to find the one you like best.

Final Thoughts

While coffee’s bright, crisp, and lively acidity can be a good thing when balanced with its natural sweetness, too much can ruin a cup. By utilizing the tips discussed above, you’ll dramatically reduce the chances of your coffee tasting sour and be that much closer to consistently brewing a perfect cup.

Lastly, if you’d like to continue furthering your coffee knowledge or if you’re looking for ways to improve your home barista skills, be sure to check out our brewing guides and the coffee basics sections of our website.

Frequently Asked Questions

Sour coffee often has a sharp, tangy taste that registers on the sides of your tongue. It’s similar to the acidity in citrus fruits but lacks sweetness or depth. If your coffee leaves a lingering, unpleasantly sharp sensation rather than a rich, balanced flavor, it’s likely sour.

Adding milk or creamer to your coffee can soften the sour taste, potentially making it more palatable, but it won’t completely eliminate it. A better solution is to use the suggestions discussed above.

No, sourness is generally not an issue with cold brew. Although it’s brewed at a lower temperature, its longer steeping time typically results in a much smoother, less acidic flavor. If your cold brew does happen to taste sour, chances are it’s under-extracted and just needs to steep longer.

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Hey there! I'm Michael, founder and editor-in-chief of Filtered Grounds. In addition to being an entrepreneur, I'm also a bit of an endurance sports junkie. Whether it's working toward my business goals or training for my next Half Ironman triathlon, a good cold brew or cup of French press plays a role in fueling my performance.