Why Does My Espresso Taste Sour And How To Dial In Your Grind Size

If your espresso tastes sharp, tart, or unbalanced—especially with a lingering sourness on the front of your tongue—you're not alone. Sour espresso is one of the most common frustrations among home baristas and even seasoned café operators. While flavor preferences vary, true sourness in espresso typically points to under-extraction, where the water pulls too few soluble compounds from the coffee grounds. The good news? This issue is often fixable with one critical adjustment: your grind size.

Grind size is the cornerstone of espresso extraction. It determines how quickly water passes through the coffee bed and how thoroughly it dissolves sugars, acids, and bitter compounds. Too coarse, and you get weak, sour shots. Too fine, and the shot becomes over-extracted, tasting harsh and bitter. Mastering the balance starts with understanding why sourness occurs—and knowing exactly how to respond.

Understanding Sour Espresso: The Science Behind Under-Extraction

Espresso extraction is a chemical process where hot water dissolves flavor compounds from ground coffee. These compounds are released in a predictable sequence: acids first, then sweetness, followed by bitterness. When the extraction stops too early—before enough sugars and body are pulled—the result is dominated by bright, acidic notes that read as sourness.

Sour espresso isn’t about the bean’s origin or roast level alone. Even high-quality, freshly roasted beans can produce sour shots if extraction parameters are off. Key factors include:

• Grind size: Coarse particles offer less surface area, slowing dissolution and reducing contact time.
• Brew time: Shots pulling under 20 seconds rarely achieve full extraction.
• Dose and yield ratio: A 1:1 or 1:1.5 ratio (e.g., 18g in, 18–27g out) is typical; deviating without adjusting grind can cause imbalance.
• Tamping pressure: Inconsistent tamping leads to channeling, where water bypasses dense areas and rushes through weak spots.

The interplay between these variables means that while grind size is the primary lever, it must be adjusted within the context of your entire setup.

“Grind size is the heartbeat of espresso. Get this wrong, and no amount of technique will save your shot.” — Luca Anzil, World Barista Championship Judge

How Grind Size Controls Extraction

Think of coffee particles like sugar cubes. A whole cube dissolves slowly in tea; crushed sugar vanishes almost instantly. The same principle applies to coffee. Finer grinds expose more surface area to water, increasing extraction efficiency. Coarser grinds reduce contact, leading to faster flow and lower extraction yields.

In practice, changing your grinder setting by just one notch can alter brew time by several seconds. Most home espresso machines operate best with a grind size that produces a 25–30 second shot for a double (18–20g dose yielding 36–40g). If your shot finishes in 18 seconds, it’s likely sour. If it takes 40+ seconds, it may be over-extracted.

Tip: Always change only one variable at a time. Adjust grind first, wait for stability, then assess the shot.

Step-by-Step Guide to Dialing In Your Grind Size

Dialing in refers to the process of fine-tuning your grind size to achieve optimal extraction. Follow this methodical approach to eliminate sourness and develop a balanced, sweet espresso.

1. Start with fresh, evenly roasted beans. Use coffee roasted within the past 2–4 weeks. Stale or unevenly roasted beans resist consistent extraction.
2. Weigh your dose and yield. Use a digital scale to measure input (dose) and output (yield). Aim for consistency—e.g., 18g in, 36g out.
3. Set your timer. Start the clock when the pump engages and stop when your target weight is reached.
4. Pull your first shot. Note the time, flavor profile, and any visual cues (e.g., thin stream, sputtering).
5. Evaluate:
   • If the shot runs too fast (<20 sec) and tastes sour → grind finer.
   • If the shot crawls (>35 sec) and tastes bitter or hollow → grind coarser.
   • If the shot is close but slightly off → make micro-adjustments.
6. Wait 30 seconds after each adjustment. Burrs retain heat and old grind particles. Let the grinder stabilize.
7. Repeat until balanced. A well-dialed shot should take 25–30 seconds, yield a rich, honey-like stream, and taste sweet, complex, and clean.

This process may take 3–5 attempts. Patience pays off in clarity and consistency.

Common Mistakes That Cause Sour Shots (and How to Avoid Them)

Even with the right grind size, other errors can sabotage extraction. Here are frequent pitfalls and their fixes:

Mistake	Why It Causes Sourness	Solution
Inconsistent dosing	Too little coffee speeds up flow, reducing extraction	Use a scale; dose to within 0.1g accuracy
Uneven tamping	Creates channels where water flows unevenly	Tamp squarely and consistently, or use a distribution tool
Low brew temperature	Cold water extracts less efficiently	Set machine temp to 92–96°C (198–205°F)
Dirty portafilter or group head	Residue blocks water flow or causes channeling	Clean group head daily; backflush with detergent weekly
Old or poorly stored beans	Stale coffee loses solubility and sweetness	Buy fresh, store in an airtight container away from light

Tip: Perform a “puck inspection” after each shot. A well-extracted puck should be firm, evenly saturated, and break apart cleanly. Wet spots or dry clumps indicate channeling.

Real Example: Fixing Sour Espresso at Home

Consider Maria, a home barista using a semi-automatic machine and a mid-range conical burr grinder. She noticed her morning espresso tasted sharply sour, despite using beans she loved in her French press. Her standard recipe was 18g dose, 36g yield, but the shot pulled in just 19 seconds.

She began by checking her grinder setting. It was on the coarsest third of its range. She adjusted it two notches finer and waited 30 seconds. The next shot took 23 seconds—closer, but still sour. Another half-notch finer brought the time to 27 seconds. This shot tasted sweeter, with notes of caramel and red apple instead of vinegar-like acidity.

Maria repeated the test the next day. With the same setting, her shot ran slightly slower due to increased room humidity affecting the beans. She made one minor coarsening adjustment. Within three days, she had dialed in a stable, repeatable grind setting that produced balanced espresso every morning.

Her key insight? Grind size isn’t set-and-forget. It must adapt to bean freshness, ambient conditions, and machine behavior.

Checklist: Dial-In Success in 7 Steps

Use this checklist each time you switch beans or notice a flavor shift:

• ✅ Use freshly roasted, high-quality beans (within 4 weeks of roast date)
• ✅ Weigh dose and yield with a precision scale
• ✅ Set brew ratio (start with 1:2, e.g., 18g in, 36g out)
• ✅ Time the shot from pump start to target weight
• ✅ Adjust grind based on time and taste: finer for sour, coarser for bitter
• ✅ Allow 30 seconds between adjustments for grinder stabilization
• ✅ Confirm consistency across 3 consecutive shots

Frequently Asked Questions

Can light roasts be sour even when extracted correctly?

Light roasts naturally emphasize acidity, which some confuse with sourness. However, well-extracted light roasts should have vibrant, wine-like acidity balanced by sweetness. True sourness—sharp, unpleasant, and one-dimensional—still indicates under-extraction, regardless of roast level.

Should I change my dose or yield if my espresso is sour?

Not initially. Dose and yield affect strength and concentration, but grind size controls extraction. First, adjust the grind to fix sourness. Once extraction is balanced, tweak dose or ratio to fine-tune body or intensity.

How often should I clean my grinder when dialing in?

Clean your grinder every 2–4 weeks, or more often if you switch bean types frequently. Old grounds trapped in burrs or chutes can skew results. A quick brush-out or full disassembly prevents stale particles from contaminating fresh doses.

Final Thoughts: Consistency Is the Goal

Sour espresso doesn’t mean bad beans or a broken machine—it means your extraction needs tuning. Grind size is the most powerful tool at your disposal. By approaching dial-in methodically, recording your changes, and tasting critically, you’ll transform inconsistent, sour shots into rich, balanced espresso.

Remember, no single grind setting works forever. Humidity, bean age, and even water quality shift daily. The skilled barista doesn’t seek a permanent setting—they cultivate the habit of recalibration. Each shot becomes a data point, each adjustment a step toward mastery.

💬 What’s your go-to method for fixing sour espresso? Share your experience or ask questions in the comments—let’s build better coffee together.