You could write an entire book about the most common mistakes in coffee brewing. In this article, we focus on the most frequent mistakes made when brewing espresso—both at home and in cafés—based on our experience. But if I had to point to just one crucial factor that can easily improve the quality of your cup, I’d say: water quality.
Table of Contents
- 1. Water and Its Impact on Flavor
- 2. Acidity – Origin and Processing
- 3. Bitterness – What Causes It?
- 4. Origin and Botanical Variety
- 5. Extraction and Intensity
- 6. Over vs. Under Extraction
- 7. Temperature and Its Influence
- 8. Summary and Practical Tips
Water and Its Impact on Flavor
Espresso is made up of 90%–92.5% water, and pour-overs of 98%–99%. Water can enhance or suppress flavor. It can intensify acidity and sweetness, but also create a rough or smooth mouthfeel, and affect the body of the coffee.
It’s worth ensuring your water is properly filtered, for example using a carbon filter jug like Brita or Dafi, and low in mineral content (50 mg – 175 mg of minerals per 1L of water). Overly alkaline water (high carbonate hardness) will neutralize acidity, while overly acidic water will make the coffee taste sharply sour or astringent.
Acidity – Origin and Processing
Acidity in coffee comes from several factors. Primarily from the natural acids contained in the coffee bean, such as: lactic, citric, malic, phosphoric, and chlorogenic acids. At the farm level, bean selection plays a role—higher quality beans are more likely to exhibit pronounced acidity. Altitude is closely linked to this as well.
Processing is one of the three key stages (farming, processing, roasting) during which flavor compounds develop in coffee. Many chemical reactions occur during processing that influence how noticeable the acidity will be in your cup.
Coffees processed using the washed method will have a different kind of acidity compared to those processed naturally or with the honey method. The washed process tends to bring out fresh, crisp acidity often associated with citrus fruits.
Sun-dried coffee will also have acidity, but—depending heavily on its origin—it’s often supported by higher sweetness, making it more reminiscent of forest fruits like strawberries or stone fruits like plums.
The honey method has four types: white, yellow, red, and black. The darker the color, the longer the de-pulped fruit dried on the bean, allowing sugars more time to penetrate the structure of the coffee seed. This has a significant impact on perceived acidity.
Almost all experimental processing methods—such as carbonic, anaerobic, lactic, acetic, thermal, extended, co-ferment, double anaerobic, cold fermentation, hyper, enzymatic, nitro—result in heightened acidity.
The final stage, which we baristas don’t control but which significantly impacts acidity, is roasting. The lighter the roast, the higher the acidity.
Bitterness – What Causes It?
Bitterness in coffee is a bit less complex. In the bean, caffeine and chlorogenic acid are inherently bitter. Since we’re talking about high-quality coffee, we don’t need to address selection—after all, that’s part of what defines Specialty Coffee. Low-quality beans with defects increase bitterness perception.
If transportation goes smoothly and no defects creep in—like improper coffee storage—this stage won’t negatively affect flavor either. Next comes roasting: the darker the roast, the more bitter the coffee.
Origin and Botanical Variety
Origin also plays a role. African coffees are naturally more acidic. You’ll find more sweet-bitterness in South American coffees—except in Colombia, where beans often exhibit some of the highest levels of acidity. Central American coffees tend to offer a good flavor balance. Meanwhile, coffee from Mexico, India, and Papua New Guinea tends to be more bitter.
Botanical variety also matters. For example, the Kenyan SL28 variety is known for its vibrant, pronounced acidity.
Extraction and Intensity
Now that we’ve covered the background, let’s move on to extraction. It’s worth noting that intensity (concentration) and extraction (dissolving compounds from the coffee) are not the same. Under-extracted coffee is more acidic because salts dissolve first, then acids, and finally sugars.
Grind too coarse, and your brew time shortens—water only dissolves a fraction of the compounds, resulting in a salty, astringent, acidic, flat brew with no sweetness. The solution? Grind finer.
Can we get the same effect by simply increasing the coffee dose? Not really. Increasing the coffee dose without adjusting water volume lowers extraction. The resulting cup will be more concentrated but sharper and less balanced.
Over vs. Under Extraction
Over-extracted coffee tastes bitter, muted, and drying on the finish. Strong but under-extracted coffee can also be bitter, but it tends to have higher acidity—these two effects are often confused. Worse than either is a weak and over-extracted coffee: too little coffee, too much water, excessive extraction, and a diluted brew. This often happens with moka pots if the brewing process isn't stopped at the right time.
If your coffee brews for too long and turns overly bitter—grind coarser.
Temperature and Its Influence
The final factor that affects coffee flavor is temperature. The higher the water temperature, the greater the extraction—and with it, more bitterness.
Summary and Practical Tips
As you can see, no flavor or factor should be considered in isolation. If your coffee doesn’t taste the way it should, ask yourself whether it’s due to the natural characteristics of the bean. If not—apply the tips above.
And if this happens in a café—talk to the barista and tell them what’s off. Their job is to match the coffee to your preferences—you don’t have to be a coffee expert. And if your home brews aren’t turning out as you’d like—drop by Java for a training session. We’ll explain everything clearly, from the standards to the most common mistakes.
Cheers!
