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

If your espresso tastes harsh, acrid, or leaves a lingering unpleasant aftertaste, you're not alone. Bitterness is one of the most common complaints among home baristas and even some café-goers. While a slight bitterness can be part of espresso’s character, excessive bitterness usually signals an extraction issue—most often tied to grind size. The good news? This is fixable. With a clear understanding of extraction dynamics and a methodical approach to adjusting your grind, you can transform your daily shot from bitter disappointment to rich, balanced delight.

The Science Behind Espresso Extraction

Espresso is made by forcing hot water through finely ground coffee under high pressure. During this process, compounds in the coffee dissolve into the water at different rates. These include acids (which contribute brightness), sugars (for sweetness), and bitter compounds (like certain alkaloids). The goal is to extract a balanced proportion of all desirable elements without over-extracting the bitter ones.

Extraction happens in stages:

• First, acids and fruit-forward notes come out quickly.
• Then, sweetness and body emerge as extraction continues.
• Finally, bitter and woody compounds are released if extraction goes too far.

When your shot runs too long or uses too fine a grind, water extracts more than it should, pulling out those late-stage bitter chemicals. This is called over-extraction. Conversely, if the grind is too coarse or the shot ends too early, you get under-extraction, which tastes sour or sharp. But bitterness is almost always a sign of over-extraction—or uneven extraction where parts of the puck are over-extracted while others aren’t.

Tip: A well-extracted espresso should taste sweet, complex, and balanced—not just bitter or sour.

Why Grind Size Matters More Than You Think

Grind size is the single most influential variable in espresso brewing. It determines how easily water flows through the coffee bed and how much surface area is exposed to hot water. Even a fraction of a millimeter difference in particle size can shift extraction dramatically.

A finer grind increases resistance, slowing down water flow and increasing contact time. This leads to higher extraction—good up to a point. But go too fine, and you risk channeling (where water finds weak spots and bypasses most of the coffee) or excessively long shots that pull out bitter compounds.

A coarser grind reduces resistance, allowing water to pass through faster. This lowers extraction, which can help reduce bitterness—but only if the original problem was over-extraction. If your shot is already under-extracted, going coarser will make it worse.

“Dialing in isn’t about chasing a timer—it’s about listening to the flavor. The palate is your best tool.” — James Hoffmann, World Barista Champion

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

Dialing in means adjusting your grinder settings until you achieve optimal extraction. This process requires patience, consistency, and attention to detail. Follow these steps carefully:

1. Start with fresh, high-quality beans. Stale or low-grade coffee will never produce great espresso, no matter how precise your grind.
2. Set your dose and yield ratio. Use a consistent dose (e.g., 18g in, 36g out) and aim for a total brew time between 25–32 seconds, including pre-infusion if applicable.
3. Run a test shot with your current grind. Note the time, taste, and appearance. Does it stream evenly? Is the crema thin or oily?
4. Evaluate the flavor:
   • If it’s bitter and dry, try making the grind slightly coarser.
   • If it’s sour and weak, go finer.
   • If it’s both bitter and sour, you may have channeling—check tamping and distribution.
5. Adjust the grinder in small increments. One notch on most grinders equals ~5–10 seconds change in brew time. Wait for the grinder to stabilize after adjustment.
6. Repeat the shot and taste again. Allow at least two full pulls after each change to confirm results.
7. Stop when flavor is balanced: Sweetness should dominate, with acidity and bitterness in harmony.

This process can take 20–40 minutes the first time, especially if starting from scratch. But once dialed in, minor tweaks maintain quality throughout the day.

Common Mistakes That Cause Bitter Espresso

Even with the right grind size, several factors can still lead to bitterness. Here are the most frequent culprits:

Mistake	Why It Causes Bitterness	Solution
Over-tamping or uneven tamping	Creates high resistance in spots, leading to over-extraction in compacted areas	Use a calibrated tamper; apply even, moderate pressure (30 lbs)
Poor distribution before tamping	Clumps cause uneven water flow and localized over-extraction	Use a distribution tool or WDT (Weiss Distribution Technique)
Old or stale coffee	Stale beans lose sweetness and amplify bitter, flat notes	Brew within 2–4 weeks of roast date
Water temperature too high	Hotter water extracts faster and more aggressively	Set machine temp to 92–94°C (198–202°F)
Dirty portafilter or group head	Residual oils become rancid and impart bitter flavors	Clean group gasket and portafilter daily

Tip: Always purge your group head before pulling a shot to rinse away old residue and stabilize temperature.

Mini Case Study: From Bitter Mess to Balanced Shot

Mark, a home barista in Portland, had been struggling with consistently bitter espresso from his semi-automatic machine. He used freshly roasted beans but couldn’t eliminate the harsh finish. His initial setup: 18g dose, 36g output, 28-second shot time, medium-fine grind.

He followed the dial-in process step by step. First, he cleaned his grinder and ensured even distribution using a simple tapping method. After pulling a shot, he noted strong bitterness and a slight channeling sound (a hissing noise mid-pull).

Instead of going coarser immediately, he tried improving distribution with a toothpick stir (a basic form of WDT). The next shot ran smoother but still tasted bitter. He then adjusted the grinder one notch coarser. Brew time dropped to 24 seconds. The shot tasted brighter but now had sour edges.

After consulting a chart and tasting notes, Mark realized he’d overshot. He went back halfway—splitting the difference—and found a sweet spot at 26 seconds. The resulting espresso was syrupy, sweet, with chocolate and red fruit notes and only a subtle, pleasant bitterness in the finish.

The lesson? Bitterness isn't always solved by coarsening the grind. Technique, cleanliness, and incremental changes matter just as much.

Checklist: How to Fix Bitter Espresso

Use this checklist the next time your espresso tastes off:

• ✅ Confirm your coffee is fresh (roasted within past month, ideally 7–21 days)
• ✅ Clean your portafilter, basket, and group head
• ✅ Check grind size: if shot time exceeds 32 seconds, go coarser
• ✅ Ensure even distribution (use WDT or gentle swirling)
• ✅ Apply consistent tamping pressure (don’t over-press)
• ✅ Verify water temperature isn’t above 96°C
• ✅ Pull multiple shots to confirm consistency
• ✅ Taste objectively: is bitterness dominant, or part of balance?

FAQ: Common Questions About Bitter Espresso

Can dark roast espresso be less bitter?

Not necessarily. Dark roasts naturally contain more bitter compounds due to extended roasting, but proper extraction can still make them smooth. The key is avoiding over-extraction. A well-dialed dark roast should taste rich and bittersweet, not acrid.

Does water quality affect bitterness?

Absolutely. Hard water (high in calcium and magnesium) can increase extraction of bitter compounds and cause scaling. Soft or distilled water lacks minerals needed for proper extraction. Use balanced water—ideally with 50–100 ppm total hardness and a neutral pH.

Should I change my dose if the espresso is bitter?

Only after adjusting grind. Dose affects concentration and flow, but grind size controls extraction speed. Start with dose stability (e.g., 18–20g), then adjust grind. Once dialed in, you can experiment with dose changes for flavor nuance.

Final Thoughts: Mastery Through Consistency

Bitter espresso isn’t a dead end—it’s feedback. Your machine, beans, and technique are communicating with you through flavor. Learning to interpret that signal, especially through the lens of grind size, transforms frustration into refinement.

Dialing in takes practice, but each adjustment brings you closer to mastery. Over time, you’ll develop intuition: recognizing the sound of a healthy pour, the look of ideal crema, the taste of balance. And when you nail it, that perfect shot—sweet, aromatic, and harmonious—makes every tweak worthwhile.

💬 What’s your go-to method for dialing in? Share your tips, tricks, or grind settings in the comments—your insight could help another barista find their perfect shot.