Every brewing decision — grind size, water temperature, brew time, ratio — is really a decision about extraction: how much of the coffee dissolves into your cup, and which parts. Once you understand extraction, you can fix almost any bad cup by reasoning about it instead of guessing.
Roasted coffee is about 70% insoluble plant fiber and about 30% material that can dissolve in water: acids, sugars, oils, caffeine, melanoidins (brown compounds formed during roasting), and hundreds of aromatic compounds. Brewing dissolves some of that soluble material into the water.
Two numbers describe the result:
- Extraction yield (EY): the percentage of the dry coffee's weight that ended up dissolved in your drink.
- Strength, or total dissolved solids (TDS): how concentrated the drink is — the percentage of the beverage that is dissolved coffee.
They're related but different. A cup can be well extracted but weak (too much water) or poorly extracted but strong (too little water).
Research from the 1950s and 1960s by MIT scientist Ernest Earl Lockhart and the Coffee Brewing Institute — the basis of today's SCA standards — found that most people prefer coffee extracted to about 18–22% of the dry coffee's weight.
| Extraction yield | Typical taste |
|---|
| Below ~18% (under-extracted) | Sour, salty, thin, lacking sweetness, short finish |
| ~18–22% (balanced) | Sweet, balanced acidity, full flavor, pleasant finish |
| Above ~22% (over-extracted) | Bitter, dry, astringent, hollow, harsh finish |
For filter coffee, the SCA's recommended strength is about 1.15–1.35% TDS. Espresso is far more concentrated — typically around 8–12% TDS — though ideal extraction yields fall in a similar range.
Why the order of extraction matters
Compounds don't dissolve at the same rate. Broadly:
- Acids and bright aromatics dissolve first.
- Sugars and heavier, sweeter compounds follow.
- Bitter, drying compounds dissolve last and more slowly.
That's why an under-extracted cup tastes sour (you got the acids without enough sweetness to balance them), and an over-extracted cup tastes bitter and dry (you kept going into the harsh compounds).
The Main Variables: Grind Size, Water Temperature, and Time
| Variable | Effect on extraction | Change it when… |
|---|
| Grind size | Finer grind = more surface area = faster, higher extraction. The most powerful lever. | Coffee is sour (go finer) or bitter (go coarser) |
| Contact time | Longer contact = more extraction | Often changes automatically with grind in drip and pour over |
| Water temperature | Hotter water extracts faster, especially sugars and heavier compounds | Light roasts taste sour (go hotter); dark roasts taste harsh (go cooler) |
| Agitation | Stirring or swirling increases extraction and evenness | The coffee bed is uneven or dry pockets form |
| Ratio | More water extracts a little more, but mainly changes strength | Coffee is too strong or too weak |
| Water chemistry | Minerals help extract flavor; alkalinity buffers acidity | Coffee tastes flat (too soft) or dull and chalky (too hard) |
For grind settings by method, see our grind size guide; for ratios, use the coffee ratio calculator.
Evenness Matters as Much as the Average
An extraction yield is an average. A cup at 20% could be a nicely even extraction — or a mix of over-extracted fine particles and under-extracted large ones, which tastes both bitter and sour. This is why:
- Grinder quality matters. Better burrs produce more uniform particles.
- Channeling — water finding easy paths through the coffee — ruins espresso and pour over by extracting some coffee heavily and some barely at all.
- Even pouring, swirling, and good puck preparation improve flavor even when the average extraction doesn't change.
You can taste your way to good extraction, but you can also measure it. A coffee refractometer measures TDS from a few drops. Then:
Extraction yield (%) = beverage weight (g) × TDS (%) ÷ dry coffee dose (g)
Example: 300 g of brewed coffee at 1.35% TDS, made with 20 g of coffee: 300 × 1.35 ÷ 20 = 20.25% extraction — right in the target range.
Refractometers are a useful tool for enthusiasts and cafés, but taste still decides. A number in the ideal range that tastes bad usually points to uneven extraction.
Water: The Overlooked Ingredient
Brewed coffee is about 98% water, and the minerals in it change extraction and flavor. The SCA's water standard targets roughly 150 mg/L total dissolved solids with moderate hardness (calcium and magnesium help extract flavor) and about 40 mg/L alkalinity (enough to soften harsh acidity without making coffee flat). Very soft or distilled water produces flat, sour coffee; very hard water produces dull, chalky coffee and scales up machines. For most people, filtered tap water is a good compromise.
| Method | How it extracts | Typical control |
|---|
| Pour over / drip | Percolation — fresh water keeps flowing through | Grind size controls flow and time; see our pour over recipe |
| French press / immersion | Coffee steeps in all the water at once; extraction slows as water saturates | Time and grind; see our AeroPress vs French press guide |
| Espresso | High pressure through a compact bed in 25–35 seconds | Grind, dose, yield, and sometimes pressure profile; see our pressure profiling guide |
| Cold brew | Very slow extraction without heat over 12–18 hours | Time and ratio; see our cold brew guide |
Common Extraction Problems and Solutions
| Taste | Diagnosis | First fix | Second fix |
|---|
| Sour, thin, salty | Under-extracted | Grind finer | Hotter water or longer brew |
| Bitter, dry, harsh | Over-extracted | Grind coarser | Cooler water or shorter brew |
| Sour and bitter together | Uneven extraction | Improve pouring or puck prep | Better grinder |
| Balanced but weak | Too diluted | Use more coffee (lower ratio) | — |
| Balanced but too strong | Too concentrated | Use more water (higher ratio) | — |
Change one variable at a time, and taste after every change.
Frequently Asked Questions
What is coffee extraction?
The process of dissolving soluble compounds from ground coffee into water. Extraction yield is the percentage of the dry coffee's weight that ends up dissolved in the drink.
What is the ideal coffee extraction percentage?
About 18–22%, based on research by Ernest Earl Lockhart and the Coffee Brewing Institute that underpins today's SCA standards.
How do I know if my coffee is under- or over-extracted?
Under-extracted coffee tastes sour, salty, and thin; over-extracted coffee tastes bitter, dry, and harsh. Adjust the grind first — finer for sour, coarser for bitter.
How do you calculate extraction yield?
Extraction yield (%) = beverage weight × TDS (%) ÷ coffee dose. For example, 300 g at 1.35% TDS from 20 g of coffee is a 20.25% extraction.
