Four variables, a diagnosis table, and the detail that ruins more home espresso than anything else: the pressurised basket that comes with almost every machine under €300.
The four variables
Espresso depends on grind, dose, temperature and time. They're all connected, which is why the classic beginner's mistake is changing two at once and never learning which one worked. Change one thing at a time.
The usual starting point for a double:
- Dose: 18 g of ground coffee (adjust to your basket size).
- Yield: 36 g of espresso in the cup. A 1:2 ratio.
- Time: 25-30 seconds from the moment the pump starts.
- Water: 90-94 °C.
One detail that changes results immediately: yield is measured in grams, not millilitres. Crema takes up volume while weighing almost nothing, so 36 ml in the cup might be 28 g of actual coffee. A €15 kitchen scale fixes more bad espresso than any other accessory.
First, check which basket you have
This explains why so many people follow the manual to the letter and still can't pull a decent shot.
Almost every domestic machine under €300 ships with a pressurised basket (also called dual-wall). It has a single tiny hole underneath that creates back-pressure artificially. It was designed so that supermarket coffee, ground months ago and to the wrong setting, would still produce something resembling crema.
The problem is that this basket cancels out the effect of your grind. However you grind, the resistance comes from the hole, not from the coffee. You get a foamy, large-bubbled crema that collapses in seconds, and a flat cup.
If your crema vanishes within ten seconds and changing the grind makes no difference whatsoever, you are almost certainly using a pressurised basket.
The fix costs between €10 and €25: buy a single-wall basket in your portafilter's diameter (usually 51, 54 or 58 mm). From then on the grind matters again, and so does everything else. It's the cheapest and largest improvement available to you.
Diagnosing what's wrong
Nearly everything reduces to two tastes, each with its own correction:
| Tastes like | What's happening | What to do |
|---|---|---|
| Sour, salty, thin, runs fast | Under-extracted: water pulled too little | Grind finer, raise the dose or lower the yield |
| Bitter, drying, harsh, drips slowly | Over-extracted: water pulled too much | Grind coarser or drop the temperature slightly |
| Sour and bitter together | Channelling: the water found a shortcut | A distribution problem, not a grind one (below) |
The mental rule: sour means under-extracted, bitter means over-extracted. You rarely need more theory than that.
Channelling: the fault nobody names
If the shot tastes sour and bitter at once, or you see a jet squirting off to one side, water has opened a channel through the puck and run through it instead of passing evenly. Through that channel it over-extracts; everywhere else it under-extracts.
Grind won't fix it. It gets fixed before you tamp:
- Distribute the coffee before tamping. A couple of taps on the side and levelling with a finger or a distribution tool is enough.
- Tamp level. How hard you press matters far less than people claim; whether it's flat matters a great deal.
- Don't knock the portafilter after tamping. That knock cracks the puck and creates the channel.
You need to re-dial every few days
Something that surprises newcomers: the same coffee wants a different grind depending on how long ago it was roasted. Freshly roasted, it's still degassing plenty of CO₂, which slows the water down; two weeks on, that drops away and the water runs faster.
So a coffee that ran in 27 seconds yesterday runs in 22 today. Nothing has broken — the coffee is a day older. Adjust and carry on. Without a grinder that offers fine adjustment this is nearly impossible to compensate for, which we cover in the grinder guide.
Pressure: 9 bar, not 15 or 19
Boxes advertise 15 or 19 bar pumps and it sounds like more is better. In fact proper extraction happens at around 9 bar at the puck; the rest is pump capacity, not working pressure. Machines with a regulating valve already bring it down themselves. It isn't a number worth paying extra for.
Water matters more than you'd think
Espresso is about 90 % water, and across much of Spain the tap water is hard. Too much mineral content flattens acidity and dulls the cup, as well as scaling up your machine. If you're in a hard-water area, even a filter jug is noticeable. We go into it in the article on water.
Which coffee to use
Medium and medium-dark roasts work well for espresso: they're more forgiving of grind errors and give body and stable crema. Our Especial Bouquet sits in that range. Light single origins are more demanding — they shine, but they punish any misstep.
Whichever you choose, it needs to be freshly roasted. If you're weighing espresso against filter for everyday drinking, we compare them in this article. And if you want to go straight to the right beans, we have a specific selection of coffee for espresso, ground or whole bean.
