Why Does My Espresso Taste Bitter Adjusting Grind Size And Tamp Pressure

Bitterness in espresso is one of the most common complaints among home baristas and even seasoned coffee lovers. While a slight bitterness can be part of espresso’s character, overwhelming or harsh bitterness usually signals an issue with extraction. The two most influential variables in pulling a balanced shot—grind size and tamp pressure—are often at the root of this problem. Understanding how these factors interact allows you to fine-tune your process and consistently produce smooth, rich espresso.

Espresso extraction is a delicate balance of water, time, temperature, and resistance. When any element is out of alignment, it can lead to over-extraction—the primary cause of bitterness. This article breaks down the science behind bitter espresso, explains how grind size and tamp pressure affect extraction, and provides actionable steps to correct your technique.

The Science Behind Bitter Espresso

When hot water passes through finely ground coffee under high pressure, it dissolves soluble compounds that contribute to flavor. These include acids (which provide brightness), sugars (for sweetness), and bitter compounds (like certain alkaloids). A well-balanced shot extracts these elements in harmony. However, when too many bitter compounds are pulled from the coffee, the result is an unpleasantly sharp, acrid taste.

This over-extraction typically occurs when:

• Water spends too long in contact with the coffee grounds.
• The surface area of the grounds is too large (overly fine grind).
• Water flow is uneven, causing channeling or inconsistent saturation.

Grind size and tamp pressure directly influence both the rate and uniformity of extraction. Even with perfect water temperature and machine calibration, poor grinding or tamping can ruin a shot.

“Extraction isn’t just about strength—it’s about balance. The difference between a vibrant shot and a bitter mess often comes down to half a millimeter in grind setting.” — Luca Marconi, Specialty Coffee Trainer & Q Grader

How Grind Size Affects Extraction and Bitterness

Grind size determines how quickly water can pass through the coffee puck. Too fine, and water struggles to move through, increasing contact time and extracting more bitter compounds. Too coarse, and water rushes through too quickly, leading to sour, under-extracted shots.

With espresso, the ideal grind size creates enough resistance to allow 25–30 seconds of extraction time for a double shot (typically 18–20g of coffee yielding 36–40g of espresso). If your shot takes longer than 30 seconds and tastes bitter, your grind is likely too fine.

Tip: Make micro-adjustments on your grinder—one notch at a time—and wait for the burrs to stabilize before testing again.

It’s important to note that different beans require different grind settings due to variations in density, roast level, and age. Darker roasts are more brittle and may need a coarser setting, while lighter roasts often require a finer grind.

Signs Your Grind Is Too Fine

• Shot time exceeds 32 seconds.
• Espresso has a dry, ashy aftertaste.
• Crema appears dark with tiger striping or collapses quickly.
• Puck is extremely hard and difficult to knock out.

Signs Your Grind Is Too Coarse

• Shot time is under 20 seconds.
• Taste is sour or thin.
• Crema is pale and bubbly.
• Uneven extraction with visible channeling marks.

The Role of Tamp Pressure in Flavor Balance

Tamping ensures even distribution and consistent density of the coffee bed. Inconsistent tamping leads to uneven water flow—water will take the path of least resistance, creating channels through loose spots in the puck. This causes parts of the coffee to over-extract (bitter) while others under-extract (sour), resulting in a muddled, often bitter overall profile.

While many believe heavier tamp pressure improves extraction, excessive force can compact the grounds too much, restricting flow and promoting over-extraction. Research shows that beyond 15–20kg of pressure, there is minimal benefit and increased risk of channeling due to uneven compaction.

Tamp Pressure	Effect on Espresso	Recommended?
Too light (<10kg)	Inconsistent puck, channeling, fast flow	No
Ideal (15–20kg)	Even extraction, stable flow, balanced flavor	Yes
Too heavy (>30kg)	Over-compaction, restricted flow, bitterness	No

More important than raw pressure is consistency and levelness. Use a calibrated tamper or practice a repeatable motion: apply firm, even pressure while keeping the tamper flat. A simple trick is to use the weight of your hand and forearm rather than muscle force from the wrist.

Step-by-Step Guide to Fixing Bitter Espresso

Follow this systematic approach to diagnose and resolve bitterness caused by grind and tamping issues:

1. Weigh and measure your dose. Start with 18–20g of freshly ground coffee. Consistency begins here.
2. Set your grinder to a medium-fine setting. Aim for a starting point where shot time is around 28 seconds. Adjust from there.
3. Distribute coffee evenly. Use a tool like a WDT (wooden needle dispersion tool) or gentle shake to prevent clumping.
4. Tamp with consistent, level pressure. Apply ~15–20kg of force using a calibrated tamper or body weight method.
5. Pull the shot and time it. Target 25–30 seconds for 36–40g of output (1:2 ratio).
6. Taste and evaluate. If bitter and slow, adjust grind coarser. If sour and fast, go finer.
7. Repeat with small adjustments. Change only one variable at a time—preferably grind—to isolate effects.

After each adjustment, purge the group head, clean the portafilter, and let the grinder settle before pulling the next shot. It may take 3–5 attempts to find the sweet spot, especially if switching beans.

Tip: Keep a log of your settings—dose, yield, time, grind setting, and tasting notes. This helps track progress and identify patterns.

Real-World Example: Home Barista Breakthrough

Sarah, a home barista in Portland, struggled with consistently bitter espresso despite using high-quality single-origin beans. Her shots took 35 seconds to yield 40g, and she noticed a sharp, lingering bitterness that masked the coffee’s natural fruit notes.

She assumed she needed to tamp harder to “seal” the puck, applying nearly 30kg of pressure. After reading about optimal tamping force, she switched to a calibrated 20kg tamper and focused on level distribution using a WDT tool. She also adjusted her grinder one notch coarser.

The next shot extracted in 28 seconds with a smoother mouthfeel and pronounced sweetness. The bitterness was gone, revealing bright citrus and chocolate notes she hadn’t tasted before. By reducing tamp pressure and slightly coarsening the grind, she achieved even extraction and a far more enjoyable cup.

Common Mistakes That Amplify Bitterness

Even with proper grind and tamp, other habits can sabotage your results:

• Inconsistent dosing: Varying coffee amounts change resistance and extraction dynamics.
• Old or poorly distributed grounds: Clumps create uneven paths for water, leading to localized over-extraction.
• Clogged shower screen: Uneven water dispersion mimics tamping issues.
• Using stale beans: Degassed coffee extracts differently and often tastes flat or harsh.
• Ignoring machine maintenance: Scale buildup affects temperature stability and pressure consistency.

“Most bitter shots I see aren’t from bad beans—they’re from rushed routines. Dialing in takes patience, but it transforms coffee from routine to ritual.” — Javier Ruiz, Barista Competition Judge

Checklist for Balanced Espresso Extraction

Use this checklist every time you prepare to pull a shot:

• ☑ Freshly grind beans (within 30 seconds of brewing)
• ☑ Dose accurately (e.g., 18–20g)
• ☑ Distribute evenly (WDT or finger leveling)
• ☑ Tamp level and firm (15–20kg, flat surface)
• ☑ Check for cracks or gaps in the puck
• ☑ Time the shot (target 25–30 seconds for 1:2 ratio)
• ☑ Taste critically—sweetness should dominate, not bitterness
• ☑ Adjust one variable at a time if needed

Frequently Asked Questions

Can water temperature cause bitter espresso?

Yes. Water above 96°C (205°F) can scald the coffee, extracting excessive bitter compounds even with correct grind and tamp. Most machines operate best between 92–96°C. If your machine allows temperature adjustment, try lowering it slightly if bitterness persists after dialing in grind and pressure.

Should I change my tamp pressure or grind size first?

Always adjust grind size first. Tamp pressure should remain consistent once dialed in. Changing multiple variables at once makes it impossible to know what fixed the issue. Establish a standard tamp (e.g., 20kg), then use grind adjustments to fine-tune extraction time and flavor.

Why does my espresso taste bitter only some days?

Variability often stems from bean freshness, humidity, or grinder retention. Coffee peaks 5–14 days post-roast. Beans older than three weeks lose sweetness and extract unevenly. Humidity changes affect grind consistency—your grinder may need daily recalibration. Clean your grinder weekly to avoid stale buildup.

Final Thoughts: Mastering the Balance

Bitter espresso isn’t inevitable—it’s a signal. It tells you that extraction is running too long or too unevenly, and the simplest fixes lie in your grinder and tamper. By understanding how grind size controls flow rate and how tamp pressure influences puck integrity, you gain control over one of the most nuanced aspects of coffee preparation.

The journey to perfect espresso isn’t about perfection on the first try. It’s about observation, adjustment, and repetition. Small, deliberate changes compound into dramatically better cups. Whether you're using a manual lever or a semi-automatic machine, the principles remain the same: consistency breeds quality.

💬 Start today: Pull a shot, taste it honestly, and make one adjustment. Share your results, ask questions, or refine your method with others. Great espresso is a conversation—one sip at a time.