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Why Does My Pour-Over Coffee Taste Too Sour? What's Causing Both Sour and Bitter Flavors? Barista's Guide to Pour-Over Coffee Extraction

Published: 2026-01-27 Author: FrontStreet Coffee

Last Updated: 2026/01/27, Why does pour-over coffee taste too sour? What's happening when your coffee is both sour and bitter? Today we'll explain why these issues occur. Generally speaking, sharp acidity and bitterness are undesirable characteristics in coffee. Sharp acidity typically indicates "under-extraction," while sharp bitterness suggests "over-extraction." But what about when coffee tastes both sour and bitter? This could be

Why is my pour-over coffee too sour? What's going on when it's both sour and bitter?

Today, I'll teach you why these situations occur. Generally speaking, both sharp acidity and sharp bitterness are undesirable phenomena in coffee. Sharp acidity might indicate "under-extraction," while sharp bitterness indicates "over-extraction." So what's happening when coffee is both sour and bitter? It could be caused by partial over-extraction and partial under-extraction.

What is "Coffee Extraction"?

Coffee extraction is simply the process where water, as a solvent, combines with soluble substances as it passes through coffee grounds, ultimately resulting in flavorful coffee liquid. In a single coffee bean, only 30% consists of soluble substances, while the remaining 70% is woody fiber. Within that 30% of soluble substances, only about 20% contributes to positive flavor compounds, while the remaining approximately 10% consists of bitter/negative flavor compounds.

Since each substance has different dissolution times and speeds, generally speaking, positive flavors are the first and most easily dissolved, while negative flavor compounds require longer periods to be dissolved. Therefore, 30% is the maximum extraction rate for coffee, but the extraction rate suitable for most people's tastes is actually between 18%-22%. This range is also considered the optimal coffee extraction rate according to the Golden Cup extraction theory from the SCA (Specialty Coffee Association).

How to Calculate Coffee Extraction Rate?

When calculating extraction rate, you need to use a coffee refractometer (TDS meter) for detection. A coffee refractometer can quickly detect the proportion of extracted coffee substances to the total coffee liquid. The main subject of concentration is the coffee liquid. (If you want to calculate concentration yourself, the formula is: weight of extracted coffee substances ÷ weight of coffee liquid. That's too complicated! Don't bother calculating it...)

The extraction rate is the proportion of extracted coffee substances to the total coffee bean weight. The main subject of extraction rate is the coffee beans/grounds, so the calculation formula is: coffee concentration × coffee liquid weight ÷ coffee bean (ground) weight.

With a refractometer, we can very conveniently calculate the coffee extraction rate. If you're calculating the extraction rate for pour-over coffee, you need to note that during the blooming stage, the coffee grounds absorb twice their own weight in water. Therefore, the coffee liquid weight calculation formula is: water poured ÷ coffee bean (ground) weight × 2.

Let's Focus on Today's Main Points!

What are the signs of under-extraction?

Sharp acidity & blandness

The most obvious sign of under-extraction in coffee is prominent acidity. During the coffee extraction process, flavor substances are released in this order: acid-sweet-bitter. In under-extracted coffee, the acidic substances from the early stages are basically extracted, but the sweet and bitter flavors are insufficient to reduce the expression of acidity and enhance the coffee's body, making the coffee taste very sharp and bland/with a short aftertaste.

What are the signs of over-extraction?

Bitterness

The bitterness mentioned here refers to a very unpleasant/unusual bitterness, but bitterness alone doesn't necessarily indicate over-extraction. First, everyone's perception of bitterness varies to some degree, while the bitterness from over-extraction is unacceptable to most people, such as a burnt bitterness.

Therefore, if everyone wants to drink a good cup of coffee, they need to achieve even extraction. Read more articles written by FrontStreet Coffee and watch more tutorial videos.