Bitter does not mean burnt
Bitter, ashy and dry do not mean the same thing. A cocoa note may suit the bean well; a distracting ashy aftertaste or puckering mouthfeel calls for closer examination. First name the impression you want to change. Then check cleanliness, bean style, concentration and brewing one at a time.
The simple check first
Check the basket, outlets and brewing area for old residue. Clean following the manufacturer’s instructions. Backflushing is not intended for every machine, and descaler does not replace a suitable coffee-oil cleaner. The right care depends on your machine.
Check the beans too. Changing the recipe will not automatically turn a very dark roast into a light, fruity coffee. If its underlying character bothers you, changing beans is a sensible decision.
Concentration or brewing problem?
Set aside a small sample of the stirred espresso and add a little hot water. If it becomes much more pleasant, intensity may have been an important part of the problem. If the unpleasant character remains, look at the process and raw material.
Adjust deliberately after cleaning
- Record dose, beverage quantity and time. Check whether extraction is very slow or uneven.
- If flow stalls badly, try one small step coarser without changing the other variables.
- For an even but very long extraction that becomes thin, try stopping earlier.
- Compare after a little cooling and note whether bitterness, dryness or only intensity decreased.
Why several causes are possible
Uneven water flow through a puck can produce contradictory impressions. The simple rule bitter means too fine is then unreliable. Check distribution and a level tamp before making a large grind adjustment.
Constantly changing the dose also makes diagnosis harder. If you use more grounds today and pull a shorter shot at the same time, you create different conditions. When troubleshooting, keep the suitable basket dose fixed at first.
Temperature as a later adjustment
If your device offers a suitable temperature setting, you can change it in a separate trial. It is no substitute for accurate quantities and even flow, however. Check the operating instructions and do not change grind and temperature at the same time.
A helpful comparison
With the same bean, compare your usual extraction with a slightly shorter one. Assess not only the initial intensity but also the aftertaste. The shorter version may become rounder, or simply more concentrated. Both give you information for the next step.
Balance to your taste
You do not need to remove bitterness completely. Coffee can be pleasantly bitter if you like it that way. The goal is a cup you want to keep drinking. A recipe with minimal bitterness is not automatically the best recipe for your bean or milk drink.