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

Espresso should be rich, complex, and balanced—not harsh or overwhelmingly bitter. Yet many home baristas and even café-goers regularly encounter a shot that leaves a burnt, acrid taste on the palate. While bitterness can stem from several factors, one of the most common—and most fixable—is incorrect grind size. The grind acts as the foundation of extraction: too coarse, and your shot runs too fast, tasting sour; too fine, and it grinds to a halt, pulling out excessive bitterness. Mastering grind size isn’t just about adjusting a dial—it’s about understanding extraction science, machine behavior, and bean characteristics. This guide walks you through diagnosing bitterness, optimizing your grind, and achieving consistently delicious espresso.

Understanding Bitterness in Espresso

Bitterness in coffee is not inherently bad. In fact, well-balanced espresso often includes a pleasant, dark chocolate-like bitterness that complements sweetness and acidity. But when bitterness dominates—especially with a charred, ashy aftertaste—it signals over-extraction. Over-extraction occurs when water dissolves too many compounds from the coffee grounds, particularly later in the brewing process when undesirable bitter elements are pulled.

The primary driver of over-extraction? Grind size that's too fine. When coffee particles are ground too finely, they increase surface area and slow down water flow through the puck. This extends contact time between water and coffee, allowing more bitter compounds to dissolve. However, other variables like dose, yield, brew time, water temperature, and tamping pressure also influence extraction. It’s essential to isolate variables and understand their interplay.

“Grind size is the most powerful lever you have for controlling extraction. It’s faster to adjust than changing your machine’s temperature or pressure.” — James Hoffmann, World Barista Champion

The Role of Grind Size in Extraction

Grind size determines how quickly water passes through the coffee bed during extraction. A finer grind slows the flow, increasing resistance and dwell time. A coarser grind allows water to move faster, reducing extraction time. The goal is to hit a sweet spot where water spends 25–30 seconds extracting 18–22% of the coffee’s soluble solids—this is considered ideal for balanced flavor.

Coffee beans vary in density, roast level, age, and origin, all of which affect how they respond to grinding. For example:

• Dark roasts are less dense and more brittle, so they tend to produce more fines (microscopic particles) when ground, increasing the risk of clogging and uneven flow.
• Light roasts are denser and require a slightly finer grind to achieve proper extraction.
• Freshly roasted beans release CO₂, which can interfere with extraction if used too soon. Letting beans rest 4–7 days post-roast stabilizes them.

Because no two batches of coffee behave exactly alike, “dialing in” is necessary every time you switch beans or notice a change in taste.

Tip: Always use freshly ground beans. Pre-ground coffee loses aromatic compounds rapidly and introduces inconsistency into your shots.

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

Dialing in means adjusting your grinder settings until you achieve a balanced shot based on taste, not just numbers. Follow this systematic approach:

1. Start with a baseline setting. Consult your grinder manufacturer or online forums for recommended settings for your machine and typical dose (e.g., 18g in, 36g out).
2. Weigh your dose and yield. Use a precision scale to measure input (coffee dose) and output (espresso yield). Aim for a 1:2 ratio (e.g., 18g coffee → 36g espresso).
3. Time your shot. Start the timer when the pump engages. Target 25–30 seconds for full extraction.
4. Taste the result. Is it sour? Too fast? Adjust finer. Is it bitter? Too slow? Adjust coarser.
5. Adjust one notch at a time. Make small changes—especially with high-quality burr grinders—to avoid overshooting.
6. Wait 3–5 minutes between adjustments. Heat buildup in the grinder alters particle size. Let it stabilize.
7. Repeat until balanced. The ideal shot should have sweetness, clarity, and a clean finish without lingering bitterness or sharp sourness.

This process may take 4–6 attempts, but each adjustment brings you closer to optimal flavor. Patience pays off.

Common Mistakes That Cause Bitter Espresso

Even with the right grind size, poor technique can still lead to bitterness. Here are frequent pitfalls:

Mistake	Why It Causes Bitterness	Solution
Over-tamping or uneven tamping	Creates channeling or excessive compaction, leading to uneven extraction and localized over-extraction	Use consistent 30 lbs of pressure; consider a calibrated tamper
Incorrect dose for basket size	Overfilling causes puck expansion and restriction, slowing flow	Match dose to basket capacity (e.g., 18g in an 18g VST basket)
Dirty portafilter or group head	Residual oils and old coffee restrict flow and introduce rancid flavors	Clean group gasket and portafilter weekly; backflush daily
Water temperature too high	Excessive heat increases extraction of bitter compounds	Set boiler temp to 92–94°C (198–202°F)
Poor distribution before tamping	Clumps create uneven paths for water, causing some areas to over-extract	Use a distribution tool or WDT (Weiss Distribution Technique)

Real Example: Fixing Bitter Shots at Home

Mark, a home barista in Portland, recently switched to a darker roast Ethiopian blend. His first few shots tasted intensely bitter, with a medicinal aftertaste. He was using a 1:2 ratio (18g → 36g), but his brew time was 34 seconds—too long. He assumed the roast was simply “bold,” but decided to troubleshoot.

He started by cleaning his grinder and checking his tamp consistency. Then, he adjusted his grind setting one notch coarser. The next shot ran in 29 seconds and weighed 35g. The flavor transformed: the bitterness faded, revealing notes of dark cherry and molasses. He made one more minor adjustment, landing at 28 seconds, and found balance. By methodically adjusting only the grind and maintaining all other variables, Mark rescued his morning ritual.

This case illustrates that bitterness isn't always the bean’s fault—it’s often a symptom of misalignment in the brewing chain.

Do’s and Don’ts of Grind Adjustment

“Every variable matters, but grind is the heartbeat of espresso. Get that right, and everything else falls into place.” — Laila Ghambari, US Barista Championship Finalist

To help you avoid common traps, here’s a quick-reference checklist:

Do:

• Use a high-quality burr grinder (preferably flat or conical)
• Grind fresh for every shot
• Keep dose and yield consistent while adjusting grind
• Record your settings in a logbook or app
• Taste objectively—don’t assume longer = stronger = better

Don’t:

• Change multiple variables at once (e.g., dose + grind + temp)
• Use blade grinders—they produce inconsistent particles
• Ignore channeling signs (spurting, uneven puck erosion)
• Assume your grinder’s “number” is universal (settings vary by model and bean)
• Rush the dial-in process; allow time between shots

Frequently Asked Questions

Can water quality cause bitter espresso?

Absolutely. Hard water with high mineral content can lead to scale buildup and alter extraction chemistry, often amplifying bitterness. Use filtered water with balanced minerals (ideal: 50–100 ppm total hardness, calcium-magnesium ratio of 3:1).

Should I change my grind size throughout the day?

Yes. As your grinder heats up during use, the burrs expand slightly, making the grind finer. You may need to coarsen the setting incrementally during long sessions. Likewise, ambient humidity and bean freshness fluctuate daily.

Is a finer grind always better for crema?

No. While crema formation depends partly on fine particles stabilizing emulsified oils, too fine a grind leads to over-extraction and thin, patchy crema. True crema comes from fresh beans, proper pressure, and balanced extraction—not just grind fineness.

Conclusion: Take Control of Your Espresso Flavor

Bitter espresso isn’t inevitable—it’s a signal. It tells you that something in your process is out of alignment, and more often than not, that something is your grind size. By learning to read the cues of your machine, your beans, and your palate, you gain control over one of the most nuanced beverages in the world. Dialing in takes practice, attention, and a willingness to experiment. But once you master the rhythm of small adjustments and thoughtful tasting, you’ll pull shots that are not just drinkable, but exceptional.

💬 What’s your go-to method for dialing in a new coffee? Share your tips, challenges, or favorite settings in the comments—let’s build a community of better espresso together.