How to Identify Sourness
Sour coffee is not the same as bright or acidic coffee. Desirable acidity tastes clean, crisp, and structured—like citrus or stone fruit. Sourness tastes sharp, aggressive, and makes you wince.
Pleasant Acidity
- • Clean, crisp finish
- • Reminds you of fruit
- • Enhances sweetness
- • Leaves you wanting more
Unpleasant Sourness
- • Sharp, biting edge
- • Makes your mouth pucker
- • Tastes like vinegar or raw lemon
- • No sweetness or balance
If you are unsure, taste your coffee as it cools. Pleasant acidity becomes more complex and fruity. Sourness becomes more aggressive and astringent.
What Causes Sourness
Sourness is almost always caused by under-extraction. You have dissolved the acids (which extract first) but have not extracted enough sugars and heavier compounds to balance them.
1. Grind Too Coarse
Low surface area means water cannot extract enough material in the available time. Acids dissolve easily even with coarse grinds, but sugars do not.
2. Water Too Cool
Low temperature reduces solubility of heavier compounds. Acids are highly soluble even at low temps, but you need heat to extract sugars and balance the cup.
3. Contact Time Too Short
If your brew drains too fast (channeling, high flow rate), water does not have enough time to dissolve the heavier compounds that balance acidity.
4. Uneven Extraction (Channeling)
If water finds paths of least resistance through your coffee bed, some grounds are over-extracted (bitter) and some are under-extracted (sour). The sour dominates.
Key Insight
Sour coffee is not a roast defect or bad beans (unless extremely light). It is an extraction problem that you can fix with brewing adjustments.
How to Fix Sour Coffee
Follow these steps in order. Make one change at a time and taste the result before adjusting further.
Step 1: Grind Finer
This is the most effective fix. Increase surface area so more material dissolves in the same time.
Try this: Go 2-3 clicks finer on your grinder. If you are on a Comandante, move from 18 to 15. If using a Baratza, go from 15 to 12.
Step 2: Increase Water Temperature
If grinding finer does not fully fix it, raise your brew temperature.
Try this: If you are brewing at 90°C, go to 93-95°C. If already at 95°C, use boiling water off the kettle (100°C).
Step 3: Extend Contact Time
If your brew finishes too fast, slow it down.
Try this: Pour more slowly to increase total brew time. Or if using immersion (AeroPress, Clever), let it steep 30-60 seconds longer.
Step 4: Improve Evenness (Reduce Channeling)
If the above steps help but do not eliminate sourness, you may have channeling.
Try this: Agitate your bloom more vigorously. Use a spoon to stir or swirl the slurry. Distribute grounds evenly before pouring.
Pro Tip
Do not adjust brew ratio to fix sourness. Ratio controls strength, not extraction. Adding more coffee to sour brew just makes it strong AND sour.
Preventing Sour Coffee
Once you dial in a coffee, sourness should not return unless something in your setup changes.
Start with proven baselines
For pour-over: 1:15 ratio, 93°C water, medium-fine grind. This gets most coffees in range and you can fine-tune from there.
Keep grinder calibrated
Burrs drift over time. If you notice increasing sourness across different coffees, recalibrate or clean your grinder.
Light roasts require more extraction
Lighter roasts are denser and require finer grinds, hotter water, or more time. Do not be afraid to push extraction higher with light coffees.