How do espresso machines hold pressure at all?
Kind of a science question: I've been hacking the electronics of a cheap espresso machine a bit to see if I can get better results, and was wondering - espresso is recommended to be brewed at around 130 psi of pressure. That's a lot. My machine is a single-boiler steam pressure machine, and from what I can tell it barely manages 5 psi when pushing water through the puck.
When I use compressed air to step up the pressure to 60psi, the water shoots through in about 1 second - a tiny bit less than the recommended 25 sec :). So how is this supposed to work in a "real" high-end machine? Seems to me the tamped coffee is never going to be able to offer up that much resistance, to where 130 psi of back pressure could be sustained.
Best Answer
I can't speak for the new high end machines that provide pressure profiling, or the cheap domestic machines, which work who knows how, but the standard system for distributing pressure on the coffee is the e61 group head, and most machine group heads are based off the original design.
The e61 group is pretty much just a system of 3 pressure valves that allows the pressure to slowly ramp up 9 bars and then maintains that 9 bars of pressure while the pump continues to work. Some versions include other steps such as pre-infusion, or on newer high-end machines the ability to create pressure profiles which adjust the pressure at any point during the espresso shot.
Also note that all the resistance HAS to come from the coffee puck, so you may be grinding too coarse or not tamping hard enough. If you need to measure the pressure from the grouphead, espresso machine techs use a device like this.
You could probably make your own at home if you are so inclined.
Pictures about "How do espresso machines hold pressure at all?"
How does espresso machine build pressure?
Pressure is created when there is resistance in the flow of water from the Espresso Machines pump to your cup, when there is no resistance in the portafilter (an empty basket) water will run through very quickly.How much pressure does an espresso machine have?
Generally, a typical espresso maker produces about 9 bars of pressure. As previously mentioned, this is equal to nine times the pressure exerted by our surrounding atmosphere. To put this into perspective, the air in a car tire is typically at a pressure of 30 PSI, or pounds per square inch.Does pressure matter in espresso machine?
The higher the pressure, the faster the coffee is extracted from the grounds. So in theory, you could get a quicker cup of coffee if you just amped up the pressure. But there's a reason that the suggested extraction time for espresso is between 25-30 seconds.Understanding Espresso: Pressure (Episode #6)
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.
Images: Ketut Subiyanto, Karolina Grabowska, Ketut Subiyanto, Ketut Subiyanto