You've probably been there. You dial in what seems like the right recipe—good beans, careful measurement, the pour-over technique you've practiced—and yet the coffee tastes off. Maybe it's sharp and sour, missing any sweetness. Or it's harsh and bitter, with a dry finish that lingers unpleasantly. You adjust something, anything, and hope the next cup is better.
Here's the thing: you don't have to guess. Once you understand extraction, you can taste a cup, identify what's wrong, and know exactly which variable to change. Extraction is the concept that ties everything together—grind size, water temperature, brew time, ratio. It's the "why" behind every brewing guide you've ever read.
What Extraction Actually Means
Extraction is simply the process of dissolving soluble compounds from ground coffee into water. When hot water meets coffee grounds, it pulls out acids, sugars, oils, and aromatic compounds—the stuff that makes coffee taste like coffee.
Here's an important detail: only about 28-30% of a roasted coffee bean is actually soluble. The rest is insoluble cellulose and fiber—the spent grounds you throw away. But even though roughly 30% can dissolve, you don't want all of it. Some of those soluble compounds taste terrible. The goal is extracting the right portion: enough to capture the good stuff, not so much that you pull out the harsh stuff.
That's where the numbers come in. The Specialty Coffee Association defines the target extraction range as 18-22% of the coffee's soluble mass. Below 18%, and you're under-extracted. Above 22%, you're over-extracted. This isn't arbitrary—it's based on decades of research dating back to Dr. Ernest Earl Lockhart and the Coffee Brewing Institute in the 1950s, and validated by modern sensory science.
You don't need a refractometer to use this concept. The principle is what matters: there's a window where coffee tastes balanced, and your job is to land inside it.
The Extraction Sequence: Why Timing Matters
Different compounds extract at different rates. This is crucial to understanding why under-extracted coffee tastes sour and over-extracted coffee tastes bitter.
Think of it like steeping tea. In the first moments, you get light, delicate flavors. Steep longer, and it becomes richer. Leave the bag in too long, and it turns harsh and tannic. Coffee works the same way, but with more complexity.
Early extraction (fast): Acids come out first. These are small, polar molecules—citric, malic, phosphoric—that dissolve quickly. They're responsible for brightness and fruity notes. Caffeine also extracts early, which is why a longer brew doesn't necessarily mean more caffeine.
Middle extraction (moderate): Sugars and Maillard compounds come next. These are the caramelization products, the toffee and brown sugar notes, the body and sweetness that balance the initial acidity. Getting enough of these is what separates a vibrant cup from a sour one.
Late extraction (slow): Bitter compounds and tannins extract last. These include phenylindanes (especially prominent in dark roasts), excessive quinic acid, and high-molecular-weight melanoidins. In moderation, some bitterness provides structure. In excess, it overwhelms everything else and leaves a dry, astringent finish.
This sequence explains everything. Stop too early, and you've only extracted the acids—hence sour coffee. Go too long, and you've pulled out the harsh late-stage compounds—hence bitter coffee. Balanced extraction means you've captured enough of each stage.
Under-Extraction: What It Tastes Like and How to Fix It
The flavor profile: Sour, sharp acidity that makes you pucker. Thin body that feels watery. A salty note, especially noticeable in espresso. No sweetness whatsoever. A quick finish where the flavor disappears immediately.
What's happening: Water didn't have enough time, heat, or surface area to dissolve the sugars and balancing compounds. You extracted the fast-moving acids but stopped before reaching the good stuff.
Common causes:
Grind too coarse (not enough surface area)
Water too cool (below 195°F/90°C)
Brew time too short
Not enough agitation or uneven saturation
Ratio too tight (too much coffee for the water)
The fix: Increase extraction. The simplest adjustment is usually grinding finer—this dramatically increases surface area and extraction speed. You can also extend brew time, use hotter water, or add gentle agitation during brewing.
If you're brewing pour-over and tasting sourness, try grinding one or two settings finer. If you're already at a fine grind, check your water temperature—anything below 195°F will struggle to extract properly, especially with lighter roasts.
Over-Extraction: What It Tastes Like and How to Fix It
The flavor profile: Harsh bitterness, like unsweetened dark chocolate or tonic water. A dry, astringent mouthfeel similar to over-steeped black tea. A hollow quality where the pleasant flavors seem buried. An unpleasant aftertaste that lingers.
What's happening: Water pulled out too much, including the bitter compounds and astringent tannins that extract last. The pleasant flavors are still there, but they're overwhelmed.
Common causes:
Grind too fine
Water too hot (above 205°F/96°C)
Brew time too long
Excessive agitation
Ratio too wide (not enough coffee for the water)
The fix: Decrease extraction. Grind coarser to reduce surface area. Shorten brew time. Use slightly cooler water, especially for darker roasts. Pour more gently to reduce agitation.
One note: darker roasts are more soluble than light roasts—their porous structure gives up compounds more easily. If you're brewing a dark roast with the same parameters you'd use for a light roast, you may be over-extracting without realizing it. Back off the temperature to around 195-198°F and consider a slightly coarser grind.
The Variables That Control Extraction
Understanding which levers to pull—and what each one does—gives you control over your brewing.
Grind Size
This is usually the first variable to adjust when troubleshooting. Grinding coffee exponentially increases surface area—a single bean has roughly 3.4 cm² of surface; ground for espresso, that same bean expands to approximately 3,400 cm². Finer grinds extract faster because water contacts more coffee simultaneously. Coarser grinds extract slower.
Beyond the grind setting itself, consistency matters enormously. Inconsistent grinds—with both fine particles (fines) and large chunks (boulders)—create simultaneous over and under-extraction. The fines extract too quickly while the boulders barely extract at all. The result is muddled, confused flavor. A quality burr grinder produces uniform particles that extract evenly.
Water Temperature
Hotter water extracts faster. The SCA recommends 195-205°F (90-96°C) at the point of contact with coffee.
For light roasts, aim for the higher end of this range—200-205°F. Lighter roasts are denser and more resistant to extraction; they need the extra energy. For dark roasts, stay toward the lower end—195-198°F. Their porous structure extracts readily, and hotter water can strip harsh compounds too quickly.
If you don't have a temperature-controlled kettle, bringing water to a boil and letting it sit for 30-45 seconds typically brings it into the right range. For more on how water affects your brew, including mineral content, we've written about that separately.
Brew Time / Contact Time
Longer contact means more extraction. Different methods have different built-in time ranges:
Espresso: 25-35 seconds
Pour-over: 2:30-4:00 minutes
French press: 4:00-5:00 minutes
AeroPress: 1:00-2:00 minutes
Cold brew: 12-24 hours
Time and grind work as inverse partners. Short contact times (espresso) demand fine grinds to achieve adequate extraction in the brief window. Long contact times (French press, cold brew) require coarse grinds to prevent over-extraction.
Agitation
Any movement that disturbs the coffee bed during brewing accelerates extraction. Without agitation, a concentration gradient forms—the water immediately surrounding particles becomes saturated, slowing further extraction. Stirring, swirling, or the turbulence from pouring brings fresh water into contact with grounds.
The bloom phase is critical agitation. Pre-wetting your coffee with 2-3x its weight in water for 30-45 seconds releases CO₂ trapped during roasting and prepares the grounds for even extraction. A vigorous bloom with lots of bubbling indicates fresh coffee.
Different methods benefit from different agitation levels. Pour-over responds well to a gentle swirl after the final pour. French press typically gets one stir after adding water. Be cautious, though—excessive agitation can push fines into the filter, slow drawdown, and cause uneven extraction.
Coffee-to-Water Ratio
More water per gram of coffee increases extraction (more solvent available to dissolve compounds). Less water decreases extraction. Common ratios range from 1:15 to 1:17 for filter coffee—meaning 1 gram of coffee to 15-17 grams of water.
But here's where it gets nuanced: ratio also affects strength, which is different from extraction.
Extraction vs. Strength: An Important Distinction
These terms often get confused, but they describe different things.
Extraction is how much you pulled out of the coffee. It's measured as a percentage of the dry coffee mass that dissolved into the water. Target: 18-22%.
Strength (technically TDS, or Total Dissolved Solids) is how concentrated the dissolved coffee is in your final cup. For filter coffee, the SCA recommends 1.15-1.45% TDS.
You can have:
**High extraction + high strength:** You pulled a lot out and didn't dilute it. Result: intense, potentially bitter.
**High extraction + low strength:** You pulled a lot out but diluted it. Result: balanced but weak-tasting.
**Low extraction + high strength:** You didn't pull enough out, but it's concentrated. Result: sour and intense.
**Low extraction + low strength:** You didn't pull enough out, and it's diluted. Result: sour and watery.
The practical takeaway: grind, time, and temperature control extraction. Ratio controls strength. If your coffee tastes balanced but too weak, use more coffee—don't change your grind. If it tastes balanced but too strong, use less coffee or more water. The extraction is fine; you're just adjusting concentration.
Troubleshooting by Taste: A Quick Reference
| If your coffee tastes... | The problem | The fix |
|---|---|---|
| Sour, sharp, thin, salty | Under-extracted | Grind finer, brew longer, use hotter water |
| Bitter, harsh, dry, astringent | Over-extracted | Grind coarser, brew shorter, use cooler water |
| Weak but balanced | Too dilute (strength issue) | Use more coffee (same grind) |
| Strong but balanced | Too concentrated (strength issue) | Use less coffee or more water |
| Both sour AND bitter | Uneven extraction | Improve grind consistency, check technique |
That last row—simultaneous sourness and bitterness—usually indicates uneven extraction rather than a simple over or under problem. This happens when some grounds are over-extracted while others are under-extracted. Common causes include inconsistent grind size, channeling in espresso, or uneven saturation in pour-over. The solution is better uniformity: a quality grinder, careful puck preparation, and consistent pouring technique.
Why Evenness Matters
Uneven extraction is the silent killer of good coffee. It produces muddled flavor—sour and bitter at the same time—because different particles are extracting at different rates.
Inconsistent grind is the biggest culprit. If your grinder produces a wide range of particle sizes, the fines will over-extract (contributing bitterness) while the boulders will under-extract (contributing sourness). No amount of recipe adjustment can fix this; the particles are fundamentally extracting at different rates.
Channeling affects espresso specifically. When water finds paths of least resistance through the puck, some coffee gets over-extracted while adjacent coffee barely extracts at all. Proper distribution, leveling, and tamping minimize channeling.
Uneven saturation affects pour-over. If your pouring technique leaves some grounds dry while others are drowning, extraction will be inconsistent. A controlled, circular pour and appropriate agitation help ensure all grounds contact water evenly.
Investing in a good grinder—even a quality hand grinder—makes a bigger difference than almost any other equipment upgrade. Uniformity is the foundation of consistent extraction.
Putting It Into Practice
You don't need a refractometer to brew great coffee. You need to taste intentionally and connect what you taste to what you can change.
Start with a standard recipe: 1:16 ratio, medium grind, water just off boil. Brew your normal cup. Taste it. Ask yourself: Is this sour or bitter? Thin or harsh? Then make one adjustment—just one—and taste again. Over time, you'll build intuition. You'll recognize under-extraction immediately and know to grind finer. You'll catch over-extraction and dial back.
The beauty of understanding extraction is that it applies to every brew method. Whether you're making pour-over, French press, or espresso, the same principles govern what ends up in your cup. The variables shift—espresso extraction happens in 30 seconds, cold brew takes 18 hours—but the framework remains: acids first, sugars second, bitter compounds last. Hit the window, and your coffee will be balanced.
Once you can taste extraction, you can troubleshoot anything.
FAQ
Why does my coffee taste sour?
Sour coffee is under-extracted. The water didn't pull enough compounds from the grounds—you got the fast-extracting acids but missed the sugars that provide balance. To fix it, grind finer, extend your brew time, or use hotter water. Any of these increases extraction.
Why does my coffee taste bitter?
Bitter coffee is over-extracted. The water pulled too much from the grounds, including the harsh compounds that extract last. To fix it, grind coarser, shorten your brew time, or use slightly cooler water. Any of these decreases extraction.
What is coffee extraction yield?
Extraction yield is the percentage of your ground coffee that actually dissolved into the water. If you start with 20 grams of coffee and 4 grams dissolve, that's a 20% extraction yield. The ideal range is 18-22%. Professionals measure this with a refractometer, but you can assess it by taste—balanced sweetness with bright but not sharp acidity indicates good extraction.
How do I know if my coffee is over-extracted?
Over-extracted coffee tastes bitter, harsh, and astringent—like over-steeped black tea. It often has a dry, puckering mouthfeel and an unpleasant aftertaste that lingers. The pleasant flavors feel buried under harshness.
Does grind size affect coffee strength?
Not directly. Grind size affects extraction—finer grinds extract more, coarser grinds extract less. Strength (concentration) is primarily controlled by your coffee-to-water ratio. However, the two can feel connected: under-extracted coffee often tastes thin and weak even if the ratio is normal, because you're missing the body-building compounds that come with proper extraction.
What's the difference between extraction and strength?
Extraction is how much you dissolved from the coffee grounds (target: 18-22%). Strength is how concentrated those dissolved compounds are in your cup (target: 1.15-1.45% TDS for filter coffee). You control extraction with grind, time, and temperature. You control strength with your coffee-to-water ratio.
Why does my coffee taste both sour and bitter?
This usually indicates uneven extraction—some grounds are over-extracted while others are under-extracted. The most common cause is inconsistent grind size, where fine particles extract too much and large particles extract too little. Other causes include channeling in espresso or uneven saturation in pour-over. Focus on grind uniformity and technique consistency.
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