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I think I read that in order to get a good espresso the espresso machine has to be able to (I may be wrong):

  • provide constant 9 bar pressure
  • must be able to provide water at constant high temperature.

However, I see many espresso machines in Amazon and a myriad of other places that are marketed as "15 bar" machine, or even "20 bar" machine. For example, I can find the De'Longhi 15 bar Pump Espresso Maker, EC702, Metal or the Gevi Espresso Machines 20 Bar Fast Heating Automatic Cappuccino Coffee Maker.

Is 15 bar or 20 bar a good thing to have, compared to 9 bar?

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I think these are mostly marketing terms. What they're saying in those ads is that the machine has a pump that is able to provide 15 bar (or more on in some cases) of pressure. In practice, the pump pressure should be a bit more than the pressure you want to brew at so that you can reach and maintain that pressure when brewing.

Having a stronger pump isn't a bad thing (and it may be the standard because of other use cases for those pumps; I'm not sure) but it's not going to give you any benefits. It's a bit like having a race car in traffic, it won't hurt but you're not going to go faster.

The 9 bar figure you're referring to is commonly cited as an ideal brew pressure. For example, James Hoffmann mentions it in his video on pressure for espresso brewing. He describes it as an ideal brewing pressure because of the associated flow rate which depends on the amount of pressure.

Of course the 9 bar figure isn't set in stone, there's definitely room for experimentation, possibly by changing the pressure during the brew (assuming the equipment supports that). An article in Barista Magazine describes Scott Rao's experimentation with pressure profiling. He had good results with a long pre-infusion where pressure increases slowly, peaking at 9 bar followed by a slow drop in pressure. With a 60+ second extraction and 25% more solubles, he got positive feedback. One of the experiments was also featured in a James Hoffmann video back in 2019.

Is 15 bar or 20 bar a good thing to have, compared to 9 bar?

To answer the question directly, I don't think it hurts (or benefits) to have that high pump pressure. As a brewing temperature though, I don't think it's used much. As explained in the first video I linked, too much pressure may further compress the coffee puck in a way that may harm the flow of water.

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  • 9 bars is the magic number because that's a proven level of pressure that can extract gasses from most roasts (to produce crema). You will still get varying levels of crema from brew pressures of about 4-5 bars and up, but 9 bars or more is useful for reliably producing the thick crema expected of espresso. Even still, with an espresso machine, the pump itself is only one variable in the pressure equation. You need a fine enough grind and a good tamp to restrict water flow and force water to squeeze through every nook and cranny of every grind. All in pursuit of that crema!
    – R Mac
    Commented Aug 3, 2021 at 23:07
  • Also you don't need a 9 bar pump to brew coffee. Obviously, or drip, pour over, etc. brew methods wouldn't work at all. If you had a weak pump and used that to make espresso, water would barely escape the basket (assuming an espresso grind size and a good tamp) because the grind size and the tamp literally restrict the flow of water. Actually you'd almost definitely burn out the pump since it would try to push water that can't be pushed. If you use a coarser grind / no tamp to compensate for a weak pump, you'll still get coffee. It just won't be espresso. (Like Aeropress.)
    – R Mac
    Commented Aug 3, 2021 at 23:11
  • @RMac Maybe, I'm not sure if it's all about the crema though. I'd argue that if you could get consistently more delicious espressos at different pressures but without or with less crema then it's still a good/better option. See also that experiment by Scott Rao where he aims for higher extraction. As I understand it, you can get the same level of extraction with less beans which might translate to higher profit margins (less coffee used, equally good taste).
    – JJJ ♦
    Commented Aug 3, 2021 at 23:12
  • Oh, in case anyone wants to try the weak pump method at home, you'll also need to pass more water through the coffee. How much more depends on the variables (strength of pump, grind size, puck density, and variance in puck density).
    – R Mac
    Commented Aug 3, 2021 at 23:22
  • Who knows? There are a lot of people who prefer pour over, cold press, Aeropress, or whatever else over espresso. Crema is a defining characteristic of espresso, though, so if you're not producing it, you're not producing espresso. As to whether anyone cares about that, not really my place to say. :)
    – R Mac
    Commented Aug 3, 2021 at 23:24
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It’s marketing BS… along the lines of “if trucks are good, monster trucks must be more gooder.”

Pump pressure means nothing without flow rate. A bicycle pump may be able to produce 120psi, but it will take an hour to pump up your kid’s wading pool. A low pressure, high flow pump could do the job in minutes.

Same idea with espresso machine pumps. Just because a pump can produce high maximum pressure at zero flow doesn’t mean it can maintain useful pressure at functional flow rates.

I have a manual machine so I adjust infusion pressure (manually) to maintain constant flow rate. If a semi-automatic manufacturer made a machine which could do that (instead of blindly pumping water) I would be interested.

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