Why Does My Coffee Taste Bitter And How To Adjust Grind Size Correctly

Bitterness in coffee isn't always a sign of poor beans or bad brewing—it's often the result of incorrect extraction caused by mismatched grind size and brewing method. While a slight bitterness can complement the complexity of certain roasts, overwhelming bitterness usually means something has gone wrong in the process. The good news? Most of it is fixable with a few precise adjustments—starting with your grind.

Coffee extraction is a delicate balance between water temperature, contact time, grind size, and brew ratio. When any one of these variables is off, the flavor profile shifts dramatically. Grind size, in particular, acts as the primary control knob for extraction speed. Too fine, and you risk over-extraction; too coarse, and your coffee comes out sour or weak. Understanding this relationship is key to eliminating unwanted bitterness and unlocking a cleaner, more nuanced cup.

The Science Behind Bitter Coffee

Bitterness in coffee arises from the extraction of certain compounds, primarily chlorogenic acid lactones and phenylindanes, which are produced during roasting and become more soluble during prolonged water exposure. These compounds contribute depth but can dominate the palate when extracted excessively.

Over-extraction occurs when water pulls too many solids from the coffee grounds, including those late-to-dissolve bitter compounds. This typically happens when:

• The grind size is too fine relative to the brew time.
• The water spends too long in contact with the grounds.
• The water temperature exceeds 205°F (96°C).

For example, using an espresso grind in a French press—which requires a 4-minute steep—results in over-extraction because the ultra-fine particles offer far too much surface area for that duration. Conversely, under-extraction produces sour, sharp flavors due to early compounds being pulled without the balancing sweetness and body from later stages.

“Grind size is the most immediate lever a home brewer has to correct flavor imbalances. It’s more impactful than changing beans or tweaking water temp.” — James Hoffman, World Barista Champion & Coffee Science Expert

How Grind Size Affects Extraction

Think of coffee grounds like sugar cubes versus granulated sugar. A whole cube dissolves slowly; powdered sugar vanishes instantly. The same principle applies: finer grinds expose more surface area to water, accelerating extraction. Coarser grinds slow it down.

Different brewing methods require specific grind sizes to achieve optimal extraction within their designated time frames:

Brew Method	Recommended Grind Size	Contact Time	Common Bitterness Cause
Espresso	Very Fine (like powdered sugar)	25–30 seconds	Over-extraction due to excessive pressure or prolonged shot time
Pour Over (V60, Kalita)	Medium-Fine (like table salt)	2.5–4 minutes	Too fine a grind causing slow flow and over-extraction
AeroPress	Medium to Medium-Fine	1–2.5 minutes	Extended steep time with fine grind
French Press	Coarse (like breadcrumbs)	4 minutes	Fines passing through filter or overly fine grind
Cold Brew	Extra Coarse (like coarse sea salt)	12–24 hours	Using medium grind leading to muddy, bitter concentrate

Mismatching grind size to your method is the most common reason for bitter coffee. Even high-quality beans can taste harsh if ground incorrectly.

Tip: Always adjust grind size before changing other variables like dose or water temperature. It’s the fastest way to correct bitterness.

Step-by-Step Guide to Adjusting Grind Size Correctly

Follow this systematic approach to dial in the right grind size for your brew method and eliminate bitterness:

1. Start with a known baseline: Use a trusted recipe (e.g., 1:16 coffee-to-water ratio, 200°F water) and a freshly roasted, medium roast bean. Avoid dark roasts initially—they’re naturally more bitter.
2. Select the appropriate burr grinder setting: Refer to the table above for a starting point. Blade grinders should be avoided—they produce inconsistent particle sizes that lead to uneven extraction.
3. Brew and evaluate: Taste the coffee. If it’s bitter and astringent, with dryness on the back of the tongue, you’re likely over-extracting.
4. Adjust coarser: Turn your grinder one notch toward coarser. Repeat the brew. Note changes in flow rate and flavor.
5. Observe brew time: For pour-over, if water drains in under 2 minutes, go finer; if over 4 minutes, go coarser. For French press, if the plunger is hard to press or the coffee tastes gritty and bitter, your grind is too fine.
6. Repeat until balanced: Aim for a clean, sweet cup with mild acidity and no lingering harshness. Small adjustments make big differences.

This process—called \"dialing in\"—should be repeated whenever you change beans, roast level, or equipment. Freshness matters: coffee loses CO₂ after roasting, which affects how water interacts with the grounds. Beans 3–14 days post-roast typically extract most evenly.

Real Example: Fixing a Bitter Pour-Over

Sarah had been struggling with her morning V60. No matter the bean, her coffee tasted burnt and bitter, even though she followed recipes precisely. She used a medium roast, 30g of coffee, 500ml of water at 200°F, and a 3-minute brew time. Frustrated, she posted in a coffee forum.

An experienced barista asked one question: “What’s your grind size?” Sarah replied, “I use the ‘medium’ setting on my blade grinder.” That was the problem. Blade grinders create a mix of fines and boulders—tiny particles over-extract (bitter), while large ones under-extract (sour). The result? A muddy, unbalanced cup.

Sarah borrowed a conical burr grinder and set it to a medium-fine grind (similar to table salt). Her brew time increased slightly to 3:20, but the coffee transformed—brighter acidity, floral notes, and no bitterness. She later upgraded to her own burr grinder and now dials in each new bag carefully. The difference wasn’t the beans or the method—it was consistency in particle size.

Do’s and Don’ts of Grind Adjustment

To avoid common pitfalls, follow this practical checklist:

Do	Don’t
Use a burr grinder for consistent particle size	Use a blade grinder for precision brewing
Adjust one variable at a time (start with grind)	Change grind, dose, and time simultaneously
Store beans in an airtight container away from light	Keep coffee in the fridge or freezer (unless long-term storage)
Grind immediately before brewing	Pre-grind coffee hours in advance
Regularly clean your grinder to prevent old, rancid buildup	Ignore grinder maintenance for months

Tip: Clean your grinder monthly by grinding 30g of grinder cleaning pellets or uncooked rice (follow manufacturer instructions) to remove oily residue.

FAQ: Common Questions About Bitter Coffee and Grind Size

Can dark roast coffee be less bitter?

Not inherently. Dark roasts develop more bitter compounds due to extended roasting, but they can still taste balanced if brewed correctly. The key is avoiding over-extraction. Try using a slightly coarser grind and shorter brew time to reduce bitterness from dark roasts.

Why does my espresso taste bitter even with fresh beans?

Espresso is especially sensitive to grind size. A shot pulling in over 30 seconds with a standard dose (18–20g) almost always indicates the grind is too fine. Adjust coarser in small increments. Also, check for channeling—uneven water flow caused by poor tamping or distribution—which can cause localized over-extraction.

Is bitter coffee harmful to drink?

No, moderate consumption of bitter coffee is not harmful. Bitter compounds like caffeine and phenylindanes may even have neuroprotective effects. However, excessive bitterness can irritate the stomach lining in sensitive individuals. If you experience discomfort, adjusting brew parameters or switching to a lighter roast may help.

Conclusion: Take Control of Your Cup

Bitter coffee doesn’t have to be the norm. More often than not, it’s a symptom of incorrect grind size rather than flawed beans or poor equipment. By understanding how particle size influences extraction, you gain direct control over flavor. Whether you're using a French press, pour-over, or espresso machine, the principle remains the same: match the grind to the method, adjust incrementally, and taste critically.

Great coffee isn’t about expensive gear—it’s about precision and awareness. Start today by re-evaluating your current grind setting. Make one adjustment. Brew, taste, and observe. Small changes compound into transformative results. Soon, that harsh bitterness will fade, replaced by clarity, sweetness, and the true character of the bean.

💬 What’s your go-to method for fixing bitter coffee? Share your experience or ask questions in the comments—let’s help each other brew better.