Why Is My Espresso Sour And How To Dial In Your Grind Perfectly

Espresso should be rich, balanced, and aromatic—complex with a hint of sweetness and a clean finish. When it tastes sour instead, something has gone wrong in the extraction process. Sourness often points to under-extraction, where not enough soluble compounds are pulled from the coffee grounds. The most common culprit? Your grind size.

Grind consistency and particle size are the two most influential variables in pulling a great shot. Even with high-quality beans and a well-maintained machine, poor grind settings can ruin your espresso. The good news: once you understand the science behind extraction and learn how to properly dial in your grinder, you can consistently produce balanced, delicious shots.

Understanding Sour Espresso: The Science of Extraction

Sourness in espresso typically indicates that the shot was under-extracted. This means water passed through the coffee puck too quickly, dissolving only the most acidic and volatile compounds early in the brewing process—compounds that contribute brightness but also sharp, unbalanced acidity when dominant.

Coffee extraction occurs in phases:

• First phase (0–30%): Acids and fruit-forward notes dissolve first. These include citric, malic, and acetic acids.
• Second phase (30–70%): Sugars and body-building polysaccharides extract, adding sweetness and mouthfeel.
• Final phase (70–100%): Bitter compounds like caffeine and lignins come out last, balancing the acidity.

If your shot stops before reaching the second phase—say, at 20–25% extraction—you’ll taste mostly those initial acids, resulting in a sour, thin, and hollow flavor profile. Achieving balance means extracting across all three phases without overdoing any single one.

“Under-extraction isn’t just about sourness—it strips espresso of its complexity. A well-dialed shot reveals layers, not just one note.” — Luca Moretti, Head Roaster at Alba Coffee Co.

The Role of Grind Size in Dialing In

Grind size controls how long water takes to pass through the coffee bed. Too coarse, and water rushes through with minimal resistance, leading to fast flow and under-extraction. Too fine, and water struggles, risking over-extraction or channeling.

Dialing in refers to adjusting your grinder to achieve optimal extraction based on variables like bean freshness, roast level, humidity, and machine performance. It’s not a one-time task; it must be repeated daily—or even multiple times per day—as conditions change.

Tip: Always purge your grinder before making adjustments. Residual old grind particles will skew results.

How Grind Affects Flow Rate and Flavor

A finer grind increases surface area and slows water flow, allowing more contact time and higher extraction yield. However, if the grind is too fine, it can compact into an impermeable puck, causing uneven flow or choking the shot entirely.

Conversely, a coarse grind creates larger gaps between particles. Water finds easy paths (channels), bypassing much of the coffee. This leads to inconsistent extraction—even if average time looks normal, parts of the puck remain dry while others over-extract.

Step-by-Step Guide to Dialing In Your Grind

Dialing in requires patience, observation, and objective tasting. Follow this methodical process to achieve repeatable results:

1. Weigh and dose consistently. Use 18–20g of coffee (depending on basket size) and weigh both input (dose) and output (yield).
2. Set a target ratio. Aim for a 1:2 ratio—for example, 18g in, 36g out. Adjust later based on taste.
3. Target brew time. Start with 25–30 seconds from button press to 36g yield.
4. Pull a test shot. Note the time, yield, and appearance of the stream (should be honey-like, not spluttering).
5. Taste critically. Is it sour? Bitter? Thin? Harsh? Sweet?
6. Adjust grind accordingly:
   • If sour and fast (<25 sec): Grind finer.
   • If bitter and slow (>32 sec): Grind coarser.
   • If sour but slow: Check for channeling or tamping issues.
7. Wait and purge. Let the grinder stabilize after each adjustment. Grind 5–10 grams and discard to clear old particles.
8. Repeat until balanced. A well-dialed shot tastes sweet, full-bodied, and finishes cleanly—no lingering sourness or harsh bitterness.

Tip: Make small adjustments—one notch at a time. Large jumps make it hard to pinpoint the ideal setting.

Common Pitfalls and How to Avoid Them

Even experienced baristas make mistakes when dialing in. Here are frequent errors and their solutions:

Issue	Likely Cause	Solution
Sour espresso despite long brew time	Channeling due to uneven tamping or poor distribution	Use a distribution tool (e.g., NSEW technique), level puck evenly, check for cracks post-tamp
Shot stalls or doesn’t reach target yield	Grind too fine or excessive dose	Coarsen grind slightly or reduce dose by 0.5g
Inconsistent shots throughout the day	Bean degassing, humidity changes, or grinder heat buildup	Re-dial every 2–3 hours; allow grinder to cool; store beans properly
Bitter and astringent	Over-extraction from too fine a grind or excessive time	Coarsen grind; aim for 28–30 seconds max

Real Example: Morning Sourness at a Busy Café

At BrewLab, a specialty café in Portland, baristas noticed sour shots during morning rush despite unchanged settings. The head barista investigated: same beans, same machine, same dose. But the grinder had been off overnight, and morning humidity was higher than usual.

They re-dialed the grind—adjusting two clicks finer than the previous day’s evening setting—and introduced a pre-infusion step to improve evenness. Within three pulls, the sourness vanished. The takeaway? Environmental factors matter. What worked yesterday may not work today.

Essential Checklist for Perfect Espresso Dial-In

Use this checklist each time you begin dialing in, especially with a new batch of beans:

• ✅ Confirm dose weight (e.g., 18g)
• ✅ Weigh output (target 36g for 1:2 ratio)
• ✅ Time the shot from pump start to target weight
• ✅ Observe stream: steady twin threads, no sputtering
• ✅ Taste objectively: sour, sweet, bitter, balanced?
• ✅ Adjust grind in small increments
• ✅ Purge grinder after each change
• ✅ Record settings (grind number, time, taste notes)
• ✅ Re-check mid-day as beans de-gas

Tip: Keep a logbook. Tracking grind settings, dates, and roast profiles helps predict future adjustments.

Frequently Asked Questions

Why does my espresso taste sour even with a 30-second shot?

A long brew time doesn’t guarantee proper extraction. If the grind is inconsistent (common with low-quality grinders), some particles extract fully while others remain under-extracted. Channeling—where water finds weak spots in the puck—also causes uneven extraction. Focus on even distribution, consistent tamp pressure, and grinder quality.

Should I change the dose or the grind first?

Start with dose stability. Once your dose is locked in (e.g., 18g), adjust the grind to control time and flavor. Changing both variables at once makes it impossible to isolate what’s affecting the shot. Only alter dose if you’re consistently hitting extremes (e.g., needing a 40-second shot), which may indicate the basket is overloaded.

How fresh should my beans be for optimal espresso?

For most light-to-medium roasted specialty coffees, wait 4–7 days post-roast before using for espresso. Freshly roasted beans release CO₂ aggressively, which can interfere with extraction and create bubbly, uneven shots. After degassing begins to stabilize, flavors become more accessible and balanced.

Mastering the Grind: Beyond the Basics

Once you’ve mastered basic dial-in, consider refining other elements that influence extraction:

• Water temperature: Lower temps (e.g., 90°C) emphasize acidity; higher (94–96°C) increase extraction. Adjust if shots are consistently sour despite correct grind.
• Pre-infusion: Wetting the puck at low pressure before full pressure helps prevent channeling and improves evenness, especially with fresher or denser beans.
• Tamping pressure: Aim for 15–20 lbs of pressure, applied evenly. Use a calibrated tamper if needed. Uneven tamping creates density gradients that lead to channeling.

Also, invest in a quality burr grinder. Blade grinders or low-end flat burrs produce inconsistent particle sizes, making true dial-in nearly impossible. Stepped or stepless professional-grade grinders offer the precision required for nuanced adjustments.

“The grinder is the most important piece of equipment in espresso. No machine can fix a bad grind.” — James Hoffmann, World Barista Champion

Conclusion: From Sour to Spectacular

Sour espresso isn’t a dead end—it’s feedback. It tells you that extraction stopped too soon, and the solution lies primarily in your grind setting. By understanding the relationship between grind size, time, and flavor, you gain control over your machine and your beans.

Dialing in isn’t magic; it’s methodical. It demands attention, consistency, and a willingness to taste critically. But the reward—a balanced, sweet, complex shot of espresso—is worth every adjustment. Whether you're at home or behind a commercial machine, mastering this skill transforms your daily ritual into an act of craftsmanship.

🚀 Ready to perfect your espresso? Grab your scale, fire up the grinder, and start dialing in today. Track your changes, trust your palate, and share your journey with fellow coffee lovers.