Why Does My Espresso Taste Bitter And How To Dial In Grind Size Correctly

Bitterness in espresso is one of the most common complaints among home baristas and even experienced coffee lovers. While a slight bitterness can be part of espresso’s character, excessive or harsh bitterness usually signals a brewing imbalance. The good news? Most of the time, this issue is fixable—and often comes down to one critical factor: grind size.

Espresso extraction is a delicate balance of water temperature, pressure, dose, yield, and time. Among these variables, grind size plays the most influential role because it directly controls how quickly water passes through the coffee bed. Too fine, and you risk over-extraction—bitter, ashy flavors dominate. Too coarse, and under-extraction leaves sour, weak notes. Mastering grind size adjustment, or “dialing in,” is essential to unlocking the full potential of your beans.

Understanding Why Espresso Tastes Bitter

Bitterness in espresso isn’t inherently bad. Coffee naturally contains bitter compounds like caffeine and certain melanoidins formed during roasting. However, when bitterness overwhelms sweetness, acidity, and body, it indicates over-extraction.

Over-extraction occurs when water dissolves too many solids from the coffee grounds. This happens when the water spends too long in contact with overly fine particles. As extraction progresses beyond optimal levels (typically around 18–22%), undesirable bitter and astringent compounds are pulled into the shot.

Common signs of over-extracted espresso:

• Prolonged shot time (e.g., more than 30 seconds for a double shot)
• Dark, almost black crema with dry, ashy aftertaste
• Flavors reminiscent of burnt chocolate, wood, or ash
• Thin body despite high concentration

Tip: If your espresso finishes extracting in over 30 seconds and tastes bitter, try coarsening your grind slightly before adjusting other variables.

The Role of Grind Size in Extraction

Grind size determines surface area exposed to water. Finer grinds increase surface area, accelerating extraction. Coarser grinds slow it down. Since espresso uses high pressure and short contact time (typically 25–30 seconds), precision in particle size is crucial.

Even small changes—a quarter turn on your grinder—can shift extraction dramatically. Blade grinders are notoriously inconsistent, which is why burr grinders are recommended for espresso. Consistent particle size ensures even extraction, minimizing both sour and bitter extremes.

It's also important to note that different grinders behave differently. A \"setting 10\" on one grinder may be drastically finer than another. Always calibrate based on results, not numbers.

“Grind size is the first and most powerful tool in dialing in espresso. It’s the difference between a muddy, bitter shot and a clean, balanced one.” — James Hoffmann, World Barista Champion

How to Dial In Grind Size Correctly: A Step-by-Step Guide

Dialing in refers to adjusting your grind size to achieve ideal extraction for a given coffee, dose, and machine setup. Follow this systematic process to find the sweet spot:

1. Weigh your dose and yield: Use a scale. Start with a standard double shot: 18g in, 36g out (1:2 ratio). Track both input and output weight.
2. Set your shot time target: Aim for 25–30 seconds total brew time, including pre-infusion if applicable.
3. Start with manufacturer settings: If your grinder has suggested espresso settings, begin there. Otherwise, use a medium-fine grind as a baseline.
4. Pull your first shot: Note the time it takes to reach 36g. Taste it critically.
5. Evaluate flavor and timing:
   • If shot is bitter and slow (over 30 sec): coarsen grind.
   • If shot is sour and fast (under 20 sec): refine grind.
   • If balanced: minor tweaks may still improve clarity or sweetness.
6. Adjust incrementally: Change grind setting by 1/8 to 1/4 turn. Wait for grinder heat stabilization (especially blade or entry-level burr grinders).
7. Repeat and record: Pull new shots, noting time, taste, and adjustments. Keep a log for consistency across sessions.

This process should take no more than 20 minutes once practiced. The goal is not just speed, but balance—where bitterness is integrated, not dominant.

Common Mistakes That Lead to Bitter Espresso

Even with correct grind size, other factors can contribute to bitterness. Here are frequent errors to avoid:

Mistake	Why It Causes Bitterness	Solution
Tamping too hard	Over-compacts grounds, slowing flow and increasing extraction	Tamp evenly with consistent 30 lbs of pressure
Using stale coffee	Old beans lose volatile aromatics; remaining compounds extract unevenly	Use beans within 2–4 weeks of roast date
Water temperature too high	Excessive heat accelerates extraction of bitter compounds	Set brew temp to 90–94°C (194–201°F)
Inconsistent dosing	Too much coffee increases resistance and extraction time	Always weigh dose precisely
Poor distribution before tamping	Clumping creates channeling, leading to uneven extraction	Use a distribution tool or WDT (Weiss Distribution Technique)

Tip: After changing grind settings, purge 2–3 blank shots to clear old grounds from the grinder and portafilter.

Real Example: Fixing Bitterness in a Home Setup

Consider Sarah, a home barista using a semi-automatic machine and a mid-range conical burr grinder. She consistently pulls shots that finish in 32 seconds and taste harshly bitter, despite using fresh, medium-roast beans.

She begins her dial-in process:

• Dose: 18g | Yield: 36g | Target time: 25–30 sec
• First shot: 32 seconds, bitter, thin mouthfeel
• Hypothesis: over-extraction due to too fine a grind

She adjusts the grinder one-eighth turn coarser. After purging, she pulls again:

• Second shot: 28 seconds, smoother, with notes of dark chocolate and caramel
• Taste test confirms reduced bitterness and improved balance

She makes one more tiny adjustment finer to boost sweetness without returning to bitterness. Final shot at 27 seconds delivers a rich, syrupy texture with a clean finish. The problem was solved—not by changing beans or machine settings, but by precise grind tuning.

Checklist: How to Prevent Bitter Espresso

Follow this checklist each time you change beans or notice off-flavors:

• ✅ Use freshly roasted coffee (within 3 weeks of roast date)
• ✅ Weigh your dose and yield accurately (±0.1g precision preferred)
• ✅ Set target brew time between 25–30 seconds for a 1:2 ratio
• ✅ Adjust grind size in small increments only
• ✅ Distribute grounds evenly before tamping
• ✅ Tamp with consistent, moderate pressure (don’t twist)
• ✅ Clean your grinder weekly to prevent buildup and static
• ✅ Record your settings for future reference

Frequently Asked Questions

Can the wrong coffee bean cause bitterness?

Yes, but less often than improper brewing. Dark roasts naturally have more bitter compounds due to extended roasting. However, even dark roasts can produce balanced espresso with proper technique. Lighter roasts aren't immune—they can taste bitter if over-extracted. Always consider roast level, but prioritize brewing parameters first.

Should I change my dose if my espresso is bitter?

Not initially. Dose affects total extraction and strength, but grind size is the primary control for extraction rate. If you’re already within a standard range (16–20g for doubles), adjust grind first. Only modify dose if you're exploring different recipes (e.g., lower-yield ristretto) or correcting puck depth issues.

How often should I clean my grinder?

For daily users, brush out coffee chaff weekly and perform a deep clean (disassemble burrs if possible) every 1–2 months. Oily residues and static buildup can cause inconsistent grinding, leading to uneven extraction and off-flavors, including perceived bitterness.

Final Thoughts: Mastery Through Precision

Bitter espresso doesn’t mean poor-quality beans or a faulty machine—it usually means an imbalance in extraction. And while many variables affect that balance, grind size remains the most immediate and effective lever to pull. By learning to read the signs of over-extraction and methodically adjusting your grind, you gain control over the entire brewing process.

Remember, no single setting works forever. Humidity, bean age, roast batch, and even ambient temperature affect how coffee behaves. True mastery lies in consistency, observation, and willingness to recalibrate regularly. Treat each session as a chance to refine your understanding, not just make a drink.

🚀 Ready to transform your morning espresso? Grab your scale, fire up the grinder, and start dialing in today. One perfectly balanced shot could be just one adjustment away.