Why Is My Coffee Sour? How to Fix Under-Extracted Pour-Over

9 min read · Updated June 2, 2026

Sour pour-over usually means under-extraction. How to tell sour from bright acidity, the one-at-a-time fix ladder, and a V60 troubleshooting table to fix it fast.

You bought good beans, weighed your dose, followed a V60 recipe, and the cup still tastes like lemon water. Sour pour-over is one of the most common and most fixable problems in home brewing, and the fix is rarely “buy different beans.” It’s almost always a small change to how you brew.

This guide is a troubleshooting hub. It starts with the quick fix, then explains what’s actually happening so you can stop changing five things at once and make one deliberate move instead.

The quick fix

If you only read one section, read this. Match your cup to a row and make the first move.

• Sour and thin, with a fast drawdown. The brew is under-extracted. Grind a little finer, use hotter water, improve the bloom, and slow the pour.
• Sour and bitter at the same time. The bed is extracting unevenly. Fix evenness first (better bloom, gentler and more even pour) before you push extraction harder.
• Bright but sweet and clean. It may not be broken. A good light roast is supposed to taste lively. Leave it alone.

Change one variable at a time and re-taste, so you learn what each move does.

Sour vs. acidic

These two words get used as if they mean the same thing, and the difference is the whole game.

Acidity is the pleasant brightness specialty coffee is prized for: citrus, berry, apple, stone fruit, florals, or a wine-like sparkle. Sourness is the unpleasant version: sharp, thin, puckering, lemon-juicey, or salty with nothing underneath. A washed Ethiopian, a Kenyan, a Gesha, or a light Nordic-style roast is meant to be bright. The warning sign is sharp sourness paired with thin body, hollow sweetness, or a short, unpleasant finish.

The simplest test: look for sweetness under the brightness. If it’s there, the coffee is probably fine. If the brightness stands alone with no sweetness, the brew is probably under-extracted.

It also helps to know that sourness isn’t one chemical you can blame. Coffee holds many organic and chlorogenic acids that shift with roast and affect aroma, bitterness, and mouthfeel as well as tartness (Yeager et al., 2021). A 2023 study even found that most individual acids sit below their detection threshold in brewed coffee, and trained tasters couldn’t pick them out when they were added on purpose (Birke Rune et al., 2023). Perceived sourness comes from the whole brew, so the fix lives in extraction rather than in hunting one acid.

What under-extraction means

Brewing is extraction: water dissolving soluble material out of the grounds. Two numbers describe the result. Strength (TDS) is how concentrated the drink is. Extraction yield is how much of the dry coffee actually dissolved into the cup. They’re related but different, so a cup can be strong and still under-extracted.

The familiar Golden Cup target centers around 1.15–1.35% strength and 18–22% extraction yield, though modern research treats preference as a broader range than one ideal box (Guinard et al., 2023). Under-extraction means you landed below that window: the water stopped before it pulled enough sweetness, body, and finish to balance the early acidity. UC Davis sensory work found sourness rises as extraction yield falls, while bitterness and burnt notes climb when both strength and extraction go high (Frost et al., 2020). For more on the full picture, see coffee extraction explained.

Why pour-over goes sour

V60 is enjoyable because it’s transparent, and frustrating for the same reason. Small changes show up clearly in the cup. Here are the usual suspects, roughly in order of how often they’re the culprit.

• Grind is too coarse. Coarse grounds have less surface area and let water flow through faster, so less dissolves. Grinding a step finer is usually the first move. See grind size for pour-over.
• Water is too cool for the roast. Cooler water extracts more slowly, which can leave a dense light roast sharp and hollow. Light roasts often want 94–96°C or near boiling; see brew temperature. Temperature mostly works by changing extraction: controlled tests found little sensory effect once strength and extraction were held constant (Batali et al., 2020).
• Contact time is too short. A fast drawdown can leave the cup incomplete. A slower, steadier pour or a slightly finer grind buys more contact.
• The bloom is weak or uneven. If the bloom doesn’t wet every ground, dry pockets stay under-extracted and taste sharp. This is common with very fresh coffee, where CO2 repels water; see resting coffee.
• Pouring is uneven. Your kettle is part of the brewer. Even with an identical recipe on paper, pour height, agitation, and where you aim the stream change how evenly the bed extracts, and the cup with it (Santanatoglia et al., 2023).
• Water chemistry. If every coffee tastes sharp or hollow regardless of technique, look at your water. Fix the brewing variables first, then investigate water.

The fix ladder

When a V60 is sour and thin, work down this list one step at a time, re-tasting after each change:

1. Grind finer by one small step.
2. Use hotter water, especially for light roasts (94–96°C, or near boiling for very light, dense coffees).
3. Add contact time with a slower pour, smaller pulses, or a slightly finer grind.
4. Improve the bloom so all the grounds are wet; wait 30–60 seconds.
5. Check the ratio. If the cup is also weak, move toward 1:15–1:16 rather than only adjusting grind.
6. Check coffee age. Very fresh light roasts can taste gassy and sharp; a few more days of rest helps.
7. Check water if every coffee comes out sharp or hollow.

The discipline of one change at a time is what turns dial-in from guesswork into something you can repeat.

When it’s sour and bitter

A cup that’s sour and bitter is a different problem, and the wrong instinct is to keep grinding finer. That combination usually means uneven extraction: water channels through some parts of the bed and over-extracts them (bitterness) while skipping others that stay sour. A 2023 study showed that past a point, grinding finer can actually make this worse by promoting non-uniform flow (Lee et al., 2023).

So aim for evenness instead:

• Wet every ground in the bloom.
• Pour gently and evenly across the bed rather than drilling the center with a hard stream.
• Ease off aggressive swirling if the bed is clogging or stalling.
• If the brew stalls and finishes dry, try going slightly coarser.

When it’s bright and sweet

Sometimes the answer is to do nothing. If the cup is lively but you can taste sweetness under the acidity, with a clean finish, that’s a well-made light roast doing what it should. Trust the sweetness test before you “fix” a coffee that’s already good.

A V60 troubleshooting table

Treat these as starting points. The cup is the final judge, and the only reliable test is brewing the same coffee twice with one thing changed.

A three-brew dial-in experiment

The fastest way to fix a sour coffee, and to learn your gear, is a controlled three-brew test. Use one coffee and a timed recipe, and change only one variable per brew.

• Brew 1, baseline. Log the coffee, roast date, dose, water, grind, temperature, recipe, drawdown, and a tasting note.
• Brew 2, finer grind. Same recipe, one step finer. Did the sourness drop and sweetness rise?
• Brew 3, hotter or more even. Keep Brew 2’s grind, then raise the temperature 2–3°C or tighten up the bloom and pour. Did it improve, or tip into bitterness?

Three cups later you’ll know which lever this coffee responds to, and you can repeat it tomorrow.

Where BeanBench fits

A static article can tell you “grind finer.” It can’t tell you whether grinding finer actually fixed this coffee, with your grinder, recipe, water, and roast age. That’s the gap BeanBench closes.

Log each attempt with the coffee, roast date, dose, water, grind, temperature, drawdown, a tasting note, and the one change you made. Over a few brews the pattern becomes obvious: this roaster’s light roasts taste best a little finer and hotter, that washed coffee needed a longer bloom, this bag was simply too fresh last week. A sour cup stops being a mystery and becomes a logged experiment you can repeat on purpose.

Why this matters for your morning cup

Morning coffee is a daily ritual, which is exactly why a sour V60 is so annoying: you did everything “right” and still got a cup that tastes unfinished. The payoff of understanding under-extraction is that you stop randomly changing things. You make one controlled move, finer grind or hotter water or a better bloom, and you taste the result. That turns pour-over from guesswork into a repeatable routine, and your good beans finally taste like the bag promised.

Why this matters for a café latte

Milk hides small mistakes, but it doesn’t erase extraction. An under-extracted base tastes thin, tangy, or sharp even under steamed milk, while an over-extracted one turns bitter and drying. A well-extracted shot tastes sweeter and rounder in milk, so the drink needs less sugar or syrup to feel complete. Whether you brew V60 or pull a shot for a latte, the loop is the same: log what you changed, taste the result, and make the next cup better.

Track it in BeanBench

Diagnose the symptom, change one thing, and let your log tell you whether it worked. In BeanBench you can record the coffee, recipe, grind, temperature, drawdown, and rating, then watch the fixes that actually work for you become obvious. From here, read coffee extraction explained, grind size, brew temperature, and resting, or pick a recipe.