Brew Vero
Barista in PajamasExtraction and strength are not the same thing
Two numbers describe every cup you brew. Confusing them is why making coffee "stronger" so often makes it worse.
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Grinders
- Conical vs flat burrs: what actually changes
- Does burr size actually matter?
- Grinder habits that quietly cost you shots
- Grind size by brew method, in microns
Beans
- Roast levels, and why they change how you grind
- Washed, natural, honey: what processing does to the cup
- How long to rest coffee, and how to store it
Espresso
Technique
When someone says a coffee is too strong, they usually mean it tastes harsh. Those are different complaints with different fixes, and telling them apart is most of what separates people who dial in quickly from people who wander.
Strength is how much coffee is in the water
Strength is measured as total dissolved solids, the percentage of the liquid that is dissolved coffee rather than water. A typical filter coffee is around 1.15–1.35% TDS. Espresso is far more concentrated at roughly 8–12%.
Strength is a preference. Some people like a heavier cup and some like a lighter one, and neither is a mistake. Add water to a brewed coffee and you lower its strength without changing anything about how it was extracted.
Extraction is how much you took out of the grounds
Extraction yield is the percentage of the dry coffee mass that dissolved into your cup. Put 20 g of coffee in, dissolve 4 g of it, and you extracted 20%.
You calculate it from strength and how much liquid you ended up with:
EY% = (TDS% × beverage mass) ÷ dose
Unlike strength, extraction is not purely preference. Take out too little and you leave the sweetness behind. Take out too much and you start dissolving compounds nobody wants.
| Extraction | Tastes like |
|---|---|
| Under, below ~18% | Sour, salty, thin, sharp, finishes abruptly |
| In the window, 18–22% | Sweet, balanced, the acidity has somewhere to sit |
| Over, above ~22% | Bitter, drying, hollow, ashy, lingers unpleasantly |
The sourness of under-extraction and the bitterness of over-extraction can appear together in the same cup when the grind is very uneven, because the fines are past 22% while the boulders have not reached 18%.
The brewing control chart
Plot strength up the side and extraction along the bottom and you get the chart the industry has used since the 1950s. The rectangle in the middle is the zone where most people, most of the time, find the coffee good.
Its usefulness is that it separates the two complaints. If your cup sits inside the extraction window but too low on the strength axis, you do not need to grind finer, you need less water. If it is strong but sits left of the window, more coffee will not help; you need to extract further.
It descends from American filter-coffee research in the 1950s, using the coffees, roasts and equipment of that era, and asking a panel of that era what they liked. It has held up better than it had any right to, but it is a preference survey, not physics. Plenty of modern light roasts are enjoyed above 22%, and some brewers deliberately aim there. Treat the window as a well-worn starting point and let your palate overrule it.
Which lever moves which
| Change | Moves extraction | Moves strength |
|---|---|---|
| Grind finer | Up, strongly | Up a little |
| Longer contact time | Up | Up a little |
| Hotter water | Up | Barely |
| More agitation | Up | Barely |
| More water, same dose | Up slightly | Down clearly |
| More coffee, same water | Down slightly | Up clearly |
Grind is the extraction lever. Ratio is the strength lever. Reach for the right one and dialling in stops being guesswork.
Do you need a refractometer?
No. A refractometer measures TDS so you can calculate extraction precisely, and it is genuinely interesting, but it is a measuring tool and not a brewing improvement. Your tongue detects the sour-to-bitter axis perfectly well. The value of the numbers is that they are comparable across days and between people, which words like "a bit sharp" are not.
Log dose, yield and rating and the Coffee Journal plots each brew on a real control chart, so you can see whether your good cups cluster somewhere your bad ones do not.
Open the Coffee Journal