Answer firstOne recipe can’t brew every bean. Roast level changes a bean’s density and solubility: light roast is dense and hard to extract, so grind finer, hotter, longer; dark roast is porous and easy to extract, so grind coarser, cooler, shorter. One line to remember: one recipe ≠ all beans.
The core rule · one recipe ≠ all beans
Bean science: density and solubility
The lighter the roast, the denser the bean and the harder its solubles release, so light roast is “hard to extract.” The darker the roast, the more porous the bean and the faster the solubles dissolve, so dark roast is “easy to extract, and easy to over-extract.” That’s why the same grind and temperature can leave light roast sour yet make dark roast ashy.
Lighter is harder to extract (push); darker is easier (ease off). Read the colour, know the direction.
The master matrix
Put the three starting recipes side by side and the direction to adjust is obvious:
Grind · temperature · ratio shift with the roast
Roast
Grind
Temp
Ratio
Light
Fine
94–96°C
1:16
Medium
Medium
90–94°C
1:15
Dark
Coarse
88–90°C
1:15
How to brew each roast
Light
finer · 94–96°C · 1:16 · longer
Medium
medium · 90–94°C (target 92) · 1:15
Dark
coarser · 88–90°C · 1:15 · shorter
Learn the direction and you’re set: the lighter the roast the more you “push” (finer, hotter, longer) to coax flavour out; the darker the roast the more you “ease off” (coarser, cooler, shorter) to avoid ashy over-extraction. Medium sits in between and is the easiest place to start.
· · ·
Common mistakes
Ignore density and you fall in
What you do
Result
Fix
Ignore bean density
bad brew
read the roast, then set the recipe
Light roast + too coarse
sour (under-extracted)
grind finer, raise temperature
Dark roast + too hot
ashy, bitter
lower temperature, grind coarser
One bean, light or medium or dark, brews into completely different cups. JWC classes get every roast level tasting sweet.
FAQ
Why grind light roast finer?
Light roast is denser and less soluble, so it extracts harder. Finer grind plus hotter water pull enough out; otherwise it’s sour and thin.
Why is dark roast so easy to over-extract?
Roasting makes beans porous and soluble, so flavour comes out fast. Use a coarser grind, cooler water and less time, or it turns ashy and bitter.
One ratio for every bean?
No. One recipe doesn’t fit all beans. Roast level changes density and solubility, so grind, temperature, ratio and time all shift with it.
What if I don’t know the roast?
Read the colour and oil: pale and dry means lighter; dark brown and oily means darker. Start from the matrix, then taste and adjust.
Dial any roast
Want light, medium and dark all tasting sweet?
From density and solubility to grind, temperature and ratio, dialed in with a mentor · from RM199 · real machines
