The basket is the small metal cup that sits inside the portafilter and holds your ground coffee. Everything the machine does to make a shot happens to what's in that cup.
Where it fits
A portafilter is the handle-and-cup part you lock into the front of the machine. One source says it comprises a filter basket, a locking mechanism and a handle or similar1. So the basket is one piece of the portafilter, not the whole thing.
Inside the basket sits the coffee. The portafilter "carries a tamped puck of coffee grounds within its basket"2. A puck is the packed disc of ground coffee that you press down (tamp) before brewing.
What the basket does during a shot
The basket has two jobs. It holds the puck in place, and it lets liquid out through its base while the grounds stay behind.
The machine's grouphead is the part the portafilter locks into. Its shower is a plate of holes that spreads pressurised water over the surface of the grounds in the basket2. The portafilter then directs high-pressure hot water through the coffee puck2.
So the basket sits right in the middle of the action. The water has to pass through the puck, then through the holes in the basket's base, before it reaches your cup.
How the design shapes the flow
Not every basket is built the same way, and the build changes where the resistance to water comes from. Two broad designs are common.
| Single-wall basket | Double-wall basket | |
|---|---|---|
| Base | Holes cover the whole base3 | An inner wall with many holes, inside an outer wall with one small hole3 |
| Where the pressure comes from | The puck itself3 | The small hole, which is meant to create back pressure3 |
| Suits | Gives more control over the extraction3 | Generally better for beginners3 |
Back pressure just means pressure pushing against the direction the water flows. In a single-wall basket the maker's blog says the basket "gets the necessary pressure for espresso extraction from the puck"3. In a double-wall basket, that small hole is meant to create it instead3.
That's the real reason the basket matters. Change the basket and you change who or what controls the flow: you, through grind and tamp, or the basket's own design.
The next pages take each of these ideas on its own. Pressurised vs unpressurised baskets covers how the two types differ, and single-wall and double-wall baskets looks at the walls in more detail.
What a basket doesn't do
It doesn't heat the water, and it doesn't make the pressure on its own in every case. The machine's pump and heater do that work. It also isn't a single standard part. Baskets differ in size and dose, and some machines only suit one type. Your manual says which basket your machine is built for, so check it before you swap anything. Basket sizes and dose range explains the size side.
A quick way to picture it
Think of the basket as a sieve with rules. The rules are written into its holes. A basket with a full base of holes lets the puck decide how fast water moves. A basket with a single small outlet decides for you.
If you already own a machine, the useful next step is to find out which kind of basket came with it. How to check which basket you have walks through that.
Where the facts come from
- Espresso machine, Wikipedia
- Espresso machine (portafilter and grouphead sections), Wikipedia
- Pressurized vs. non-pressurized baskets, Breville
More on baskets
Pressurised vs Unpressurised BasketsHow pressurised and unpressurised espresso baskets differ, who each type suits, and how to tell which one your machine uses.
Single-Wall and Double-Wall BasketsWhat single-wall and double-wall mean for an espresso basket, how the two are built, and which coffee each is meant for.
Basket Sizes and Dose RangeHow an espresso basket's size, its stated dose range and the coffee you put in relate, using a maker's own manual as the guide.