Extraction is how much of the ground coffee dissolves into the water. Too little and the cup tastes sour and thin. Too much and it tastes bitter and drying. In between, it tastes sweet and balanced. Four things control it: grind size, contact time, water temperature, and how much you stir or agitate.
Strength is a separate thing. It is how concentrated the cup is, and the ratio of coffee to water sets it. Keeping those two ideas apart is the most useful thing you can learn about brewing, because it tells you which dial to turn when a cup is not right.
What dissolves, and in what order
Only about 30% of a roasted coffee bean can dissolve in water. The rest is woody plant material that stays behind as grounds. Of that dissolvable 30%, you only want about two thirds in your cup, and the order it comes out in is what makes that true.
- Acids and bright flavours come out first. They dissolve fastest. On their own they taste sour and sharp.
- Sweetness and body come next. Sugars and the heavier flavours take longer.
- Bitterness comes last. The slowest, heaviest compounds taste bitter, harsh, and drying.
So a brew that stops too early is all acid with nothing to balance it: under-extracted. One that runs too long has pulled out the bitterness at the end: over-extracted. A good cup stops after the sweetness and before most of the bitterness.
That is why sour and bitter are opposite problems with opposite fixes, and why the first question in fix sour, bitter, or weak coffee is always which one you taste.
The four dials
| Dial | To extract more | To extract less | How big a change |
|---|---|---|---|
| Grind | Finer | Coarser | The biggest; adjust this first |
| Time | Longer | Shorter | Large; tied to grind in most brewers |
| Temperature | Hotter | Cooler | Smaller; a few degrees at a time |
| Agitation | Stir or swirl more | Stir less | Small but real |
Grind works by changing surface area. Finer grounds expose more coffee to the water, so flavour dissolves faster. It also slows water down in a pourover or espresso, so a finer grind usually means a longer brew too. See calibrating the grind.
Time is simply how long water and coffee stay in contact. In a French press or AeroPress you set it directly. In a pourover, the grind sets it, which is why grind and time move together there.
Temperature changes how fast everything dissolves. Hotter water extracts faster. It is a finer dial than grind; see water temperature for coffee.
Agitation is stirring, swirling, or pouring hard. It keeps fresh water moving past the grounds, so they extract faster and more evenly.
Strength is the other half
Extraction tells you how much came out of the coffee. Strength tells you how much water it is spread through. They are independent, so a cup can be:
| Under-extracted | Well extracted | Over-extracted | |
|---|---|---|---|
| Too strong | Intense and sour | Rich but heavy | Intense and harsh |
| Just right | Sour, sharp | Sweet and balanced | Bitter, drying |
| Too weak | Thin and sour | Pleasant but watery | Thin, hollow, bitter |
Read across a row and the strength stays the same; only the extraction changes. Read down a column and the extraction stays the same; only the strength changes.
- Fix strength with the ratio. More coffee per gram of water is stronger; less is weaker. The ratio calculator does the arithmetic.
- Fix extraction with the four dials. Usually grind first.
The most common mix-up is “weak” versus “sour”. A cup that tastes watery but pleasant needs more coffee. A cup that tastes sour needs a finer grind, even if it also seems weak. See weak versus under-extracted.
The ratio nudges extraction a little too: more water passing through the same coffee dissolves a bit more of it. That is why a lungo espresso tastes more bitter than a normal shot, not just longer; see espresso ratios.
The numbers, if you want them
You never need to measure extraction to make good coffee. Your tongue is a fine instrument. But the numbers explain the advice everywhere else on this site.
- Extraction yield is the percentage of the dry coffee’s weight that ended up in the cup. The widely used target for filter coffee is 18 to 22%.
- Strength is measured as total dissolved solids, or TDS: the percentage of the drink that is dissolved coffee. Filter coffee usually tastes best at around 1.15 to 1.45%. Espresso is far stronger, roughly 8 to 12%.
The two are linked by a simple sum:
Extraction yield = TDS × weight of coffee in the cup ÷ dose
For example, the pourover recipe uses 20g of coffee and 320g of water. About 280g ends up in the cup, because the grounds hold on to the rest. If that cup measures 1.35% TDS, it contains 3.8g of dissolved coffee: 3.8 ÷ 20 is a 19% extraction. Right in the range.
Measuring TDS takes a coffee refractometer, a specialist tool. It is useful for cafés and for people who love the detail. For everyone else, taste does the same job.
Even extraction matters too
The four dials set the average extraction. A cup also suffers when the coffee extracts unevenly, with some grounds over-extracted and others barely touched. That cup tastes sour and bitter at the same time, and no single dial fixes it.
The usual causes:
- Uneven grinding. A blade grinder makes dust and boulders together. The dust over-extracts while the boulders under-extract. A burr grinder is the fix.
- Dry pockets. Grounds that never get properly wet barely extract. Stir or swirl to wet everything, and bloom a pourover.
- Channeling. Water finds a fast path through the coffee and skips the rest, a common problem in espresso and pourover. See dialing in espresso.
Sour and bitter at the same time walks through each fix.
Putting it to work
When a cup is not right, taste it and ask two questions in this order:
- Is it sour or bitter? That is extraction. Change the grind one step, finer for sour and coarser for bitter.
- Once it tastes balanced, is it too strong or too weak? That is strength. Change the ratio.
Change one thing at a time. The Brew Compass does exactly this for each method on the site, and turns what you taste into one change for the next cup.