Why Does My Brewed Coffee Taste Sour? Why Is Pour-Over Coffee So Acidic? What Causes Under-Extraction in Coffee?

Lately, more and more people who used to drink nothing but dark roasts have started exploring light roasts. As specialty coffee culture spreads, everyone wants to taste those graceful floral and fruity notes for themselves.

The catch is that light roasts are far less forgiving than dark ones — the failure rate is much higher — so people often come into FrontStreet Coffee's shops asking for troubleshooting help. By far the most common complaint is: "my brewed coffee is too sour." Coffee does contain acids — that much is unavoidable. But what most people describe isn't merely "has acidity"; it's acidity that is sharp, thin, and hard to drink.

FrontStreet Coffee has written about this many times, and because every bean behaves differently, there's no one-size-fits-all fix. But that's fine! Today we'll explain why brewed coffee can taste sharply sour. Once you understand the root cause, the remedy follows naturally.

The Balance of Flavors in Coffee

Besides acidic compounds, coffee also carries sweetness, bitterness, and salinity, and these tastes exist in constant mutual balance. When a cup tastes too sour — too strong, too sharp, too dominant — it means the acids make up too large a share of the cup, or the other flavors too small a share. The other tastes get masked while the acidity is amplified, leaving nothing but that stinging sourness. As FrontStreet Coffee has noted before, over-sour cups are extremely common for a simple reason: acidic compounds dissolve faster than anything else during extraction.

The Extraction Order of Coffee Flavors

Acidity, sweetness, and bitterness are the three main flavors we extract when brewing, and each dissolves at a different speed: acids first, then sweetness, and finally bitter compounds. Here's an analogy FrontStreet Coffee likes to use. Take 5g each of granulated sugar, brown sugar, and rock sugar, representing acidity, sweetness, and bitterness respectively, and drop them into the same cup of hot water at the same time. They all start dissolving together, but the granulated sugar, being small with the largest total surface area, dissolves completely first. The brown sugar finishes second, and the rock sugar — the largest of the three — dissolves last. (Cube sugar: playing the role of rock sugar.)

Understanding Sharp Acidity — and Fixing It

Map this example onto coffee extraction and the relationship between flavors becomes clear. If you cut the brew short, the acids — which dissolve first and fast — will dominate the cup, while sweetness and bitterness barely show up because they haven't had time to dissolve in meaningful amounts. The result is a conspicuously sour coffee. But if you let the extraction run longer and pull more from the grounds, the added sweetness and bitterness dilute the acids' share of the cup, and suddenly the coffee no longer tastes so sour!

Practical Solutions for Reducing Acidity

So the fix is straightforward: raise the extraction yield. Grinding finer, raising water temperature, extending brew time, and increasing the water dose all push extraction upward. Of these four, extending brew time and increasing water volume are the most reliable, because the first two — under certain conditions such as a very short total brew time or an over-fresh (highly degassing) roast — can actually make the acidity worse. FrontStreet Coffee therefore recommends adjusting brew time first.

For actual brewing, light-roast, high-density beans can refer to the article "How to Brew Light Roast Coffee?", which covers how to handle light roasts that tend to clog. For medium-light roasts or deeply fermented (anaerobic-style) beans, see "Three-Stage Brewing Method." As long as you keep the total brew time within the appropriate range for each style, a sharply sour cup becomes very hard to produce.

FrontStreet Coffee Recommendation

If bright acidity simply isn't your thing, or you'd like to train your palate with gentler examples first, these FrontStreet Coffee beans are worth trying with your pour-over setup:

FrontStreet Coffee Ethiopia Yirgacheffe Guodingding — a gentle introduction to light roasts. Citrus, berry, and floral notes with a green-tea-like sweetness; the acidity is soft and fruity rather than piercing, which is exactly what a well-extracted light roast should taste like.

FrontStreet Coffee Jamaica Blue Mountain No.1 — neither intensely fruity like African coffees nor heavy and bitter like dark roasts, but beautifully balanced across sweet, sour, bitter, and aromatic. Expect cream, caramel, chocolate, nut, honey, and a whisper of fruit, with a smooth body and clean, lingering finish. Frequently called the specialty coffee "almost everyone can love."

FrontStreet Coffee PWN Indonesia Golden Mandheling — dark roasted, very low acidity, with a thick, long body of herbal and dark chocolate notes and a faint earthiness. If you'd rather sidestep acidity altogether, this is the classic choice for fans of bold, mellow cups.