Coffee is more than just a drink – it is both a science and an art.
Brewing the perfect cup of coffee requires knowledge, precision, and finesse. A crucial, often overlooked factor is the grind of the coffee beans. This not only affects the extraction time but also the acidity of the coffee – and thus the entire taste experience.
Why does my coffee taste sour?
Many coffee lovers ask themselves this question.
The answer often lies in the details – more precisely: in the grind size.
A grind that is too coarse leads to underextraction – the water does not dissolve enough aromas, and the coffee tastes unpleasantly sour.
However, a grind that is too fine causes over-extraction – the coffee becomes bitter and flat.
👉 The correct grind is therefore key to a balanced coffee flavor. Choosing a low-acid coffee variety is also important, as it can help to make the taste experience even more harmonious.
Is acid in coffee bad?
No – acidity is not a flaw, but an important component of flavor.
It gives the coffee freshness, complexity and fruitiness, especially with high-quality Arabica beans.
Please note:
- Arabica contains more natural acid than Robusta .
- Light roasts emphasize acidity more than dark roasts.
- The grind size and brewing method determine how pronounced the acidity is.
Espresso is particularly sensitive to the grind size – if it's set incorrectly, it can quickly taste too sour or too bitter. Learn here how to prepare your perfect espresso .
Main causes of sour coffee
If your coffee tastes sour, the following points could be the cause:
- Too coarse a grind leads to underextraction – the coffee becomes too acidic.
- Water that is too cold: below 90 °C it does not dissolve enough flavorings.
- Bean type: Arabica beans naturally have more acidity.
- Light roast: preserves more coffee acids.
💡 Tip: Adjust the grind to the bean, roast, and brewing method – this is the fastest way to better taste.
The science behind grind size and extraction
The grind size determines how much contact surface the water has with the coffee grounds.
The finer the grind, the larger the surface area – and the slower the extraction process.
- Finer grind: more surface area → longer extraction → risk of bitterness.
- Coarse grind: less surface area → faster extraction → risk of acidity.
The correct extraction time determines whether your coffee tastes fruity and lively or sour and flat.
How the grind size affects the coffee acidity
The grind size has a huge influence on the perception of acidity:
- Finely ground coffee emphasizes acidity because more organic acids are dissolved.
- Coarsely ground coffee reduces acidity because there is less contact time.
- Arabica beans bring more natural acidity into play than Robusta.
- The finer the grind, the slower the extraction – and the more intensely the acidity is emphasized.
Those seeking the perfect taste should carefully adjust the grind . Even small changes can significantly alter the balance of acidity, sweetness, and body.
Interaction of roasting and grind size
The roasting of the beans also influences how strongly you perceive the acidity in the coffee – and which grind size you should choose:
- Light roast: Emphasizes the natural acidity and fruity notes of the beans.
👉 A finer grind can help shorten the extraction time and balance the flavor. - Medium to dark roast: Contains less acid, but more roasted aromas.
👉 A slightly coarser grind can reduce bitterness and highlight sweetness.
💡 Tip: Experiment with small grind size adjustments when switching between light and dark roasts – you will taste distinct differences.
Common mistakes with sour coffee – and how to avoid them
Sour coffee rarely happens by accident.
Here are the most common mistakes:
- The grind is too coarse.
- The water is too cold (below 90 °C).
- The beans are old or have been stored incorrectly.
- Incorrect brewing method.
- The machine is dirty.
The correct grind for every brewing method
Each brewing method requires a specific grind to perfectly balance acidity and extraction:
- Espresso: very fine, similar to salt.
→ High pressure, short brewing time, strong aroma. - French Press: coarse, about like breadcrumbs.
→ Longer brewing time, fuller-bodied flavor. - Pour Over (e.g. V60, Chemex): medium grind, similar to coarse sand.
→ Uniform extraction, balanced acidity. - AeroPress: medium to fine.
→ Flexible depending on the recipe – experiment with the grind size. - Cold Brew: very coarse.
→ Long extraction time, mild and low in acidity. - Moka pot: medium to fine.
→ Combination of pressure and heat, strong flavor.
💡 Fine-tuning is everything: Even a small change in the grind size can completely change the taste.
Practical tips for a balanced coffee taste
- Use fresh beans.
Freshly roasted beans provide more aroma and natural sweetness. - Check the water temperature.
Optimal: 90–96 °C.
Too cold = more acidity, too hot = more bitterness. - Adjust the grind setting.
Is your coffee too sour? → Grind it finer.
Is your coffee too bitter? → Grind it coarser. - Dose correctly.
A good ratio is about 1:16 (1 g coffee to 16 g water). - Maintain the machine.
Clean equipment guarantees pure taste without foreign flavors.
If your coffee still tastes sour
Even if you do everything right, the coffee can still taste sour.
Then check the following:
- Water temperature: Ensure your water temperature is between 90 and 96 degrees Celsius. Water that is too cold can lead to insufficient extraction, which will accentuate the acidity.
• Coffee-to-water ratio: Check that you are using the correct amount of coffee. Too high a water-to-coffee ratio can intensify a sour taste.
• Care and maintenance of your equipment: Deposits in your coffee machine can affect the taste of the coffee. Regular cleaning is crucial.
• Brewing time: A brewing time that is too short can also lead to a sour taste. Consider slightly increasing the brewing time.
Systematically try and adjust – that's how you'll quickly find your ideal setting.
☕ Conclusion: The grind size is your key to perfect coffee enjoyment
The balance between acidity, sweetness and body depends directly on the grind size.
Even small adjustments can transform a sour coffee into a harmonious, aromatic one.
Whether espresso, pour over or French press – if you understand the influence of the grind on the acidity, you can specifically control the taste of your coffee.
👉 In short: The grind size is your compass on the way to the perfect cup of coffee.
FAQ
1. How do I find the right grind for my coffee?
The optimal grind size depends on the brewing method, bean type and roast :
- Espresso: very fine (like salt)
- Filter coffee: medium grind, for balanced acidity and body
- Pour Over / Chemex / V60: medium grind (like coarse sand)
- French Press: coarse (like breadcrumbs)
If the grind size and extraction time are right, the coffee tastes harmonious and aromatic.
2. Why does my espresso taste sour?
Sour espresso often results from underextraction : the water flows through the coffee grounds too quickly or the grind is too coarse. Also check the water temperature (90–96 °C) and the freshness of the beans .
3. How does roasting affect the acidity in coffee?
- Light roast: emphasizes acidity and fruity notes → possibly grind finer to shorten extraction time.
- Dark roast: reduces acidity, roasted aromas dominate → possibly grind a little coarser to balance bitterness.
4. Can I control the acidity in my coffee?
Yes! The acidity can be precisely controlled through grind size, brewing method, water temperature, brewing time, and roast level . Experiment to find your personal taste.
5. How do I prevent coffee from becoming bitter?
Bitterness is usually caused by over-extraction (too fine a grind or too long a brewing time).
- For light roasts: shorter extraction time or finer grind.
- For dark roasts: grind slightly coarser and check the brewing time.
