A home roast tastes grassy, or flat and bready
Coffee you roasted yourself tastes sharp and vegetal, or dull and papery, despite being freshly roasted and rested.
Safety note
Roasting involves high temperatures and flammable chaff. Never leave a roast unattended, roast only in a well-ventilated space with equipment designed for it, and empty the chaff collector after every batch.
Causes, most likely first
There are 5 likely causes, listed with the most probable first. Work down the list and change one thing at a time, so that when the problem goes away you know which change fixed it.
Cause 1 of 5 · Commonly the cause
What roasters call underdevelopment — most often a roast dropped very soon after first crack
- How to check
- Did you drop within a minute or so of first crack starting?
- What to change
- Extend the time after first crack on the next batch, keeping everything else the same. Grassy, sharp and thin is the signature.
Cause 2 of 5 · Commonly the cause
What roasters call baking — usually blamed on a roast that stalled or crawled
- How to check
- Did the roast seem to sit at a similar colour for a long stretch?
- What to change
- Change the pace on the next batch, keeping the end point the same, and compare. Flat, bready and papery is how roasters describe it, and it is not recoverable in the cup. The explanation is craft knowledge: two studies that made a baked roast deliberately used opposite recipes.
Cause 3 of 5 · Reported, not independently verified
Too large a batch for the roaster
- What to change
- Use the load your machine's manual states. A batch the roaster was not designed around does not move through the heat as intended, and one maker warns that too small a batch is as much a problem as too large.
Cause 4 of 5 · Commonly the cause
Not enough resting time
- What to change
- Taste the same batch across a fortnight before concluding anything about the roast. Very fresh coffee brews unpredictably and tastes closed.
Cause 5 of 5 · Reported, not independently verified
Slow cooling after the drop
- What to change
- Use the machine's cooling cycle and let it finish. Until they are cooled, hot beans go on roasting, so a slow cool gives a darker roast than the one you chose.
If none of these fixes it
Check the cleaning and descaling guide. Equipment that needs maintenance can cause several of these symptoms at once, and no change of recipe will correct it.
Work through it for your setup
The causes above are general. These go to the part of a diagnostic that takes this symptom one check and one change at a time.
- Grassy, raw, bready or burnt in a way that seems wrong for the coffeeThe possibilities, the quickest check and one thing to change first
- It foams hard, brews unevenly or tastes sharp, and the bag was roasted very recentlyThe possibilities, the quickest check and one thing to change first
- Roast loss calculator
Related issues
Learn the technique
Step-by-step guides to the skills this problem comes from.