Short answer: if your bottomless portafilter isn't showing you anything useful, the basket is probably the reason. A pressurised basket hides what the puck is doing. That's its whole job.
This is the step almost everyone skips, and it's why a lot of people buy a bottomless portafilter, see a wall of foam, and conclude the portafilter is faulty. It isn't. The basket is doing exactly what it was designed to do.
The two kinds of basket
A pressurised basket — also called dual-wall, or just "the one it came with" — has a second wall underneath with one tiny hole in it. Water passes through the coffee, collects in the gap, and is forced out of that single hole. That artificial back-pressure produces a thick, foamy crema no matter what the coffee underneath is doing.
An unpressurised basket — single-wall — is just a mesh of holes. There's no gap and no valve. The only resistance is the puck itself. Everything you did before you pressed the button now shows up in the cup.
You can tell them apart in about five seconds. Take the basket out and look at the underside. One small hole in a solid base means pressurised. Dozens of tiny holes across the whole base means unpressurised.
Why the pressurised one exists
It's not a cheap part or a con. It exists so that pre-ground supermarket coffee and an inexpensive grinder can still produce something that looks and tastes like espresso. Without it, coffee that's too coarse or unevenly distributed would simply gush through in eight seconds.
If you're drinking pre-ground coffee and you're happy with your shots, the pressurised basket is the right choice and there's nothing here to fix.
Why it breaks a bottomless portafilter
A bottomless portafilter exists for one reason: to let you watch the underside of the puck and see where water is escaping unevenly. That's how you learn what to change.
Put a pressurised basket in one and you've defeated it. The valve sits between the puck and your eyes. Everything comes out of a single hole, foamy and identical, whether the puck was perfect or a disaster. You've bought a window and left the curtain shut.
So if you've just fitted a bottomless portafilter and it looks like nothing changed, check the basket before you assume the portafilter is wrong.
What changes when you switch
Be ready for it to get worse before it gets better. That is normal and it is not a sign you've made a mistake.
- Your grind will suddenly matter. Pre-ground coffee is almost always too coarse for an unpressurised basket. Shots run fast, pale and sour until you grind finer.
- Your distribution will suddenly matter. Clumps become channels. This is where a WDT tool stops being optional — stirring the bed for ten seconds is the single highest-value thing you can do.
- Your tamp will suddenly matter. Not how hard, how level. A tilted puck sends water down one side.
Most people need about a week of pulling shots before an unpressurised basket beats the pressurised one they left behind. Then it keeps getting better, which the pressurised basket never does.
Should you actually switch?
Switch if you have a grinder you can adjust, you're buying whole beans, and you want to keep improving.
Don't switch yet if you're using pre-ground coffee or a blade grinder. Nothing downstream can fix a grind you can't control, and you'll just be frustrated. Fix the grinder first — it does more than any accessory we sell.
And if you're not sure, you don't have to commit. Keep the basket that came with your machine. Baskets swap in seconds.
What to buy, in order
- An unpressurised basket in your size. Most machines have one available, and some — including many Breville models — include one in the box that people never unwrap.
- A WDT tool. One size works with every basket. This is the part that makes an unpressurised basket behave.
- A tamper that stops at the same depth every time. Level matters more than force, and a depth collar removes the guesswork. Breville 54mm machines take a 53mm tamper — here's why the two numbers differ.
- A bottomless portafilter, last. It is a diagnostic tool, and it's worth having once there's something to diagnose.
That order matters. Buying the bottomless portafilter first is the most common way people end up disappointed.
A note for DeLonghi Dedica owners
The Dedica ships with a pressurised basket, and it's the machine where this catches people most often. It also takes a three-ear portafilter that most 51mm listings don't fit — we cover that separately, including the part we don't stock.
Not sure which basket you've got? Send us a photo of the underside and we'll tell you. Gabriel answers these himself, and he'd rather answer an email than process a return.