9Barista Stovetop Espresso

The 9Barista is a stovetop espresso maker that actually makes espresso. It looks a little like a moka pot, but inside, a patented two-boiler system, designed by a Cambridge jet engineer, produces 9 bars of pressure and brew water at 93°C on an ordinary hob, with no pump and no electronics. The only moving part is a spring-loaded valve. Here’s how it works, how to use it, and where it came from.

The short version

• Two boilers: one makes the pressure, the other sets the temperature.
• About 9 bars and 93°C, the espresso standard, on any hob.
• About 20 g of fine coffee in a 53 mm portafilter, for roughly 40 g of espresso.
• No pump, no electronics, one moving part.
• Made in Cambridge, UK, and designed to be repaired.

How does the 9Barista work?

Daily Coffee News traced the water’s journey:

1. The lower boiler is sealed. As it heats on the hob, pressure builds until it reaches 9 bars.
2. At 9 bars, a calibrated spring-loaded valve opens and sends super-heated water, at about 179°C, into a heat exchanger coiled inside the upper boiler.
3. The upper boiler is open to the air through a small chimney, so its water can’t get hotter than 100°C (at sea level). It cools the brew water to 100°C. You can warm your cups over the steam.
4. A finned heat exchanger on the outside cools the water further, to about 93°C.
5. The water is pushed up through finely ground, tamped coffee in a 53 mm bed, and the espresso collects in the top cup.

“The upper boiler uses the property that boiling water open to the air must be at 100°C, at sea level,” inventor Will Playford told Daily Coffee News. “The pressure and temperature profile are fixed. We wanted to keep the machine as simple and reliable as possible.”

How do you use a 9Barista?

1. Fill the lower boiler to the fill line, about 120 ml.
2. Screw on the middle section, which divides the water between the two boilers.
3. Turn the top cup upside down: its base is a 53 mm portafilter. Grind about 20 g of coffee into it and tamp.
4. Fit the silicone basket cap, flip the cup and screw it on. (Playford says the cap isn’t really needed with a properly fine grind.)
5. Put it on the hob. You don’t need to adjust the heat; the machine should brew the same way every time, giving about 40 g of espresso.

How is it different from a moka pot?

	Moka pot	9Barista
Pressure	About 1 to 2 bars (9Barista’s figure)	About 9 bars
Brew temperature	Not controlled	About 93°C
Coffee bed	Loose basket	Tamped 53 mm portafilter
Result	Strong coffee	Espresso

The body is cast brass, the seals are standard metric silicone O-rings, and there’s a safety valve that opens at 12 bars, Daily Coffee News reports. 9Barista says every part is replaceable and that it publishes service guides.

Who made it?

William Playford studied jet engineering at the University of Cambridge, where his PhD at the Whittle Laboratory measured heat transfer in gas turbine engines. The idea came during his PhD, the university’s engineering department says: espresso needs high pressure, controlled temperature and precise parts, the same three things as a jet engine. His first sketch dates from 2013.

He used the lab’s instruments to measure espresso machines, built and tested dozens of prototypes, and machined some production samples on the Whittle Lab’s CNC machines. The company’s story adds that he’d been analysing the thermal performance of his own La Pavoni lever machine at night in the garden shed.

9Barista launched on Kickstarter at the London Coffee Festival in 2019, reached its funding target within four days, and raised over £54,000, according to Cambridge and Daily Coffee News. The first batch of 170 machines was due in October 2019. The machine was later named “highly commended” for the most innovative product award at the festival in 2022, the company says.

General guidance only. The lower boiler is under pressure: never open it while hot, and follow the maker’s instructions.

9Barista vs other methods

• Moka pot: the classic stovetop coffee maker, at lower pressure.
• Manual espresso press: hand-powered espresso, with a lever or press.
• Lever espresso: spring and direct-lever machines like the La Pavoni.
• Espresso: the full guide to espresso.

Explore every pressure method in the pressure chapter.