Rocket Espresso: Wrong brew pressure from factory? - Page 2

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HB
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#11: Post by HB »

Pino wrote:Here the response from Luca Bezzera on Espresso TV.
I'm baffled by his explanation. A vibratory pump is not "weak" or a "toy" as he says, at least at espresso flow rates. He mentioned Illy recommendations, but according to their website (PDF), it's certainly not 11 bar:
Coffee Dose: 7 gm +/- 0.5 gm
Coffee Temp: 190° - 197°F
Pump Pressure: 9 bar +/- 0.5 bar
Extraction Time: 25 - 30 seconds (not including pre-infusion)
Volume in the cup: 25ml (25g weighed on a gram scale or measured without crema in a beaker)
But don't take my word for it or Espresso TV guests -- try it yourself. Adjust the brew pressure to 7 bar, 9 bar, and 11 bar. Don't choose small increments like 0.5 bar, use at least 2 bar. Take notes. I'm betting the difference in taste/texture will be obvious.
Dan Kehn

PeetsFan

#12: Post by PeetsFan »

HB wrote:I'm baffled by his explanation. A vibratory pump is not "weak" or a "toy" as he says, at least at espresso flow rates. He mentioned Illy recommendations, but according to their website (PDF), it's certainly not 11 bar:


But don't take my word for it or Espresso TV guests -- try it yourself. Adjust the brew pressure to 7 bar, 9 bar, and 11 bar. Don't choose small increments like 0.5 bar, use at least 2 bar. Take notes. I'm betting the difference in taste/texture will be obvious.
https://www.illy.com/en-us/eshop/coffee ... s-P-1#6607

Pump Pressure: 15 bar

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HB
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#13: Post by HB »

PeetsFan wrote:Pump Pressure: 15 bar
I've seen that a lot in marketing literature and assume it was written by someone with no knowledge of how a vibratory pump works or espresso.



That's the zero flow rate maximum pressure. Maybe it sounds impressive? :lol:
Dan Kehn

JRising
Team HB

#14: Post by JRising »

Wow. Luca Bezzera totally misses the point, or just avoids it because he's trying to explain to the toddler that didn't seem to realize that boiler pressure was different than pump pressure and his english is difficult.
Different machines have different pumps. Positive displacement pumps like the rotary pumps in commercial machines are designed to provide more flow than the plumbing can handle so that pump pressure is a constant and brew pressure (the pressure drop across the puck) depends entirely on the prep (unless there are flow control devices or something involved).
Vibration pumps supply more than enough flow to brew with, but not terminal flow for the machine, without the portafilter and prep in place, the pressure at the output of the pump is far less than pump pressure when actually brewing. As Ken and most people here know and have posted in graphs, the vibe pumps flow rate changes with the backpressure it's working against, thus the prep is important to get that ~9 Bar drop over a standard prep in a 58mm basket. Of course, in a little 55mm basket, the prep is going to be taller... If the grounds aren't coarser, a higher pressure will be required to pass through that thicker barrier at the exact same flow rate...
But no, Luca, you're right. Little machines are set at 11 bar full-flow to make the pump more powerful. :roll:

PeetsFan

#15: Post by PeetsFan replying to JRising »

His family's been building espresso machines since 1901. He might know what he's talking about. And I know that Breville machines are typically higher than 9 bar as well. So there must be some reason why they do this on those machines, because frankly, the machine will likely be more reliable at a lower pressure setting.

Pino

#16: Post by Pino »

PeetsFan wrote:His family's been building espresso machines since 1901. He might know what he's talking about.
Exactly!

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Jeff
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#17: Post by Jeff »

Around 60 years ago somebody decided that "9 bars" was the right pump pressure for the Italian blends and roasts of the day. Maybe they looked at the spring rate of their lever product and calculated that it was close to 9 bar when fully compressed. (Which is higher than the typical operating pressure of spring levers, at least as I recall Paul Pratt's statements.) Maybe it was that it was the fastest shot that they could pull. (There's some strong evidence that above 8-9 bar somewhere, the puck undergoes "secondary compression" and the pressure/flow characteristics change significantly.) Cafes and restaurants are labor-intensive businesses. Cut even seconds off an oft-repeated task and you serve customers more quickly, increasing satisfaction and potentially increasing profitability. It wasn't that spring lever machines were making bad espresso. Some the attractions of a pump-driven machine was that it was easier, faster, cleaner, safer, and potentially more compact on the counter.

9 bar has been written in stone by the official Italian espresso marketing organization.

None of that really matters.

If you don't believe the arguments based on "physics", or the opinions of the many that have tried adjusting the brew pressure on their machines and doing enough testing to have confidence that 11 bar is not a great pressure for the OPV of a machine, vibe pump or otherwise, try it yourself. Drop your pressure by something significant, maybe 2 bar lower (edit: meaning 7-8 bar instead of the more typical 9-10 bar). Try it for a while. One shot, even 10 shots may not be enough to be confident of what you're tasting. Adjust up or down from there. Decide for yourself.

PeetsFan

#18: Post by PeetsFan »

Jeff wrote: If you don't believe the arguments based on "physics", or the opinions of the many that have tried adjusting the brew pressure on their machines and doing enough testing to have confidence that 11 bar is not a great pressure for the OPV of a machine, vibe pump or otherwise, try it yourself. Drop your pressure by something significant, maybe 2 bar lower (edit: meaning 7-8 bar instead of the more typical 9-10 bar). Try it for a while. One shot, even 10 shots may not be enough to be confident of what you're tasting. Adjust up or down from there. Decide for yourself.
I don't wish to disrespect any of the fine people here who have studied this in great detail. In truth, I don't understand the subject, and the interrelationship between pressure and flow. I don't understand if it's 9 bars at the pump or at the puck, and I don't know how or where it's measured in my machine. I don't know if it even matters; I thought that, in a hydraulic system, pressure is always the same everywhere, but here we have a system where a pump pressurizes fluid which is already under pressure, and it then passes through a small orifice and then into a larger orifice. So it would seem that pressure increases, then increases more, then decreases, but I truly don't know.

I do understand your challenge: Try it yourself and make your decision based on taste. Even so, with all of the other variables, this would be difficult for me. Pressure goes up, then my grind must be finer. And some roasts may respond well, while others don't. I'll just keep my machine at 9 bars per the indicator and relish my blissful ignorance.

As for Luca Bezzera, I own a Bezzera so I'm his fan. And if he's wrong, that's just part of the charm of Italian engineering (although my Bezzera has a rotary pump, not a toy pump). It's funny: I hate buying Chinese products with poor English in the manuals, but the grammar mistakes in the Bezzera's GUI are somehow charming.

HedonisticBeans (original poster)

#19: Post by HedonisticBeans (original poster) »

Turns out mine is 12 bar