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What Causes Sourness in Pour-Over Coffee? How to Make Perfect Pour-Over Coffee? Does Under-Extraction Make Coffee More Sour?

Published: 2026-01-27 Author: FrontStreet Coffee

Last Updated: 2026/01/27, After experiencing the "passionate" baptism of summer, many friends have become fascinated with light roast coffee that boasts floral and fruity notes. Because light roast coffee retains more acidic compounds, the resulting iced coffee has a richer juiciness, making it more suitable as a comfort during this hot summer. But soon, some friends discovered that their own

Why Your Light Roast Coffee Tastes So Sour

After experiencing the "passionate" baptism of summer, many friends have begun to fall in love with light roast coffee featuring floral and fruity notes. Because light roast coffee retains more acidic substances, the resulting iced coffee offers a richer juice-like quality, making it more suitable as a comforting refreshment during these hot summer days.

However, many friends soon discover that the coffee they brew at home doesn't have the same sweet and sour balance as what they taste in the shop! Instead, it often exhibits sharp, abrupt acidity that feels unpleasant. This leaves them puzzled - why does their homemade coffee turn out so sour? Today, FrontStreet Coffee will share the reasons why brewed coffee might develop that sharp acidity!

Why Does Brewed Coffee Taste So Sour?

It's quite simple. The coffee flavors and tastes we experience are primarily created by the different proportions between three types of substances: acidity, sweetness, and bitterness. When we taste a coffee that seems very sour, it indicates an imbalance among these flavors! This doesn't necessarily mean there are too many acidic substances - it could also mean there's insufficient content of sweet and bitter substances, causing the acidity to stand out prominently.

Therefore, to make your brewed coffee less sour, we can increase the extraction of sweet and bitter substances while reducing the proportion of acidic compounds in the coffee. This will result in a less acidic brew! To achieve this, we need to enhance "extraction efficiency"! Because coffee's acidic, sweet, and bitter substances have different dissolution rates due to their varying molecular sizes. Acidic substances are the most easily dissolved, so they begin to release in large quantities at the start of extraction. While acidic substances are releasing, sweet and bitter substances also dissolve simultaneously, but their dissolution rates are much slower than acidic substances, so their quantities dissolved at this stage are relatively small. As extraction progresses, they gradually increase their dissolution rates - first the sweet substances, then the bitter ones.

Since bitter substances are not particularly pleasant and in large quantities can mask the other two flavors, our ideal extraction should end just before bitter substances begin to release in large quantities. This keeps the proportion of bitter substances in the coffee extremely minimal. Not only does this make the coffee richer and more full-bodied, but it also prevents bitterness from becoming prominent and unpleasant, while allowing the acidity to be softened! To achieve this, we need to make adjustments based on our tasting experience. The adjustable elements include:

1. Reduce Coffee-to-Water Ratio

The option to reduce the coffee-to-water ratio applies when your coffee exhibits sharp acidity while also being very concentrated! This means the coffee not only has high acidity but also high strength.

This situation might occur because too little hot water was used, preventing it from extracting the later-stage coffee compounds and also failing to provide sufficient "room to develop" for the coffee compounds. This results in prominent acidity alongside high coffee concentration. We can solve this problem by reducing the coffee-to-water ratio! By increasing the amount of water used, we not only extend the extraction time but also dilute the concentration. Because more sweet and bitter substances can be dissolved, the acidity is softened, making the coffee more palatable.

2. Extend Extraction Time

However, if your coffee is very sour but lacks sufficient concentration (meaning it's quite weak), this indicates the coffee hasn't been extracted enough and needs a higher extraction rate to draw out more flavor compounds from the coffee. In this case, extending the extraction time would be an excellent approach.

There are three ways to extend extraction time. First, you can change the filter cone - replace a fast-flowing filter cone with a slower one, such as Kono or Kalita Wave filters, which significantly slows drainage time and gives hot water more extraction time. If you're already using these filters but the flow rate is still fast, we can adjust by grinding finer to increase the density between coffee particles, making it more difficult for water to pass through, effectively extending extraction time.

Finally, you can use multi-stage pouring. The same amount of water will yield different extraction times depending on the pouring technique. The more stages in your pour-over process, the longer the total extraction time. However, high returns often come with high risks - overly long extraction times can lead to over-extraction. Therefore, when dividing your pours, it's best to pay attention to how the parameters work together and find the optimal number of stages for your brewing process! (This also applies to adjusting your grind finer)

3. Increase Water Temperature

If the above steps can no longer be improved, we can achieve our goal by raising the water temperature! Since water acts as the solvent for coffee, its temperature determines the efficiency of dissolution - the higher the water temperature, the stronger the extraction efficiency!

Generally, FrontStreet Coffee brews light roast beans at 90-92°C. When these temperatures fail to extract sufficient coffee compounds, FrontStreet Coffee will try increasing the water temperature by 2-3°C, allowing the hot water to have higher extraction efficiency and extract more compounds in a shorter time! However, it's important to remember that "high returns come with high risks" - excessively high water temperature can easily lead to immediate over-extraction. Therefore, try not to let the water temperature exceed 94°C, as this allows for better control over the coffee extraction.