Boiler bar pressure-What does it really tell us?

Beginner and pro baristas share tips and tricks.
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Fullsack

#1: Post by Fullsack »

"My pressure is set a hair under .9 bar" "I set mine at 1.1 bar"

Using Dan's technique from Buyers Guide to the A3 the linked video and a Scace, I set both my home and office A3's to 200 degrees at the portafilter. To achieve this temp, the home machine required a setting just a hair above 1.1, the same temp on the office machine was a little below 1.0 bar. Without the Scace, I would have had the impression, if I have my setting the same as some other H-Ber with an A3, I would get the same temp at the pf they do.
LMWDP #017
Kill all my demons and my angels might die too. T. Williams

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HB
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#2: Post by HB »

First of all, I would measure with the same pressure gauge before assuming onboard gauges on two espresso machines are in agreement. Even so, I would not expect two boilers at precisely the same boiler pressure would deliver the exact same brew temperature. The flush amount, variance in manufacturing specifications, differences in thermosyphon efficiencies due to scale, ambient temperature, and inlet water temperature could all have an impact.

HX Love notes other considerations:
What is the 'right' boiler pressure setting? wrote:Most home baristas set their espresso machine's pressurestat somewhere between 0.8 and 1.2 bar (measured at the top of the cycle) and then determine the flush amount to bring the group to the target temperature. I prefer the pressurestat setting on the lower end of the acceptable range because it slows the overheating of the water in the heat exchanger. The drawbacks are that it diminishes recovery time and especially steam production, some espresso machines to the point where they no longer can create microfoam well. But if you're preparing drinks only for yourself and perhaps a couple friends, the lower end of the boiler pressure range is easier to manage temperature-wise than the upper end. The barista's job is easier in the former case because the rebound time is long enough that the difference in brew temperature between a delay of 15 seconds and 25 seconds after the flush and the beginning of the extraction isn't dramatic. In contrast, a miscalculation of ten seconds risks producing an over-temperature extraction (very dark initial crema, black edges) for a pressurestat setting at the high end of the acceptable range.

The right boiler pressure for a prosumer machine is therefore the pressurestat setting that meets your drink preparation pace, and to some degree, your experience level. Finally, keep in mind that commercial HX machines in general are less influenced by the flush because of their heavier groups and larger heat exchangers. Manipulating the brew temperature outside of the "comfort zone" of such espresso machines by flushing requires more attention to timing the length of the flush and the rebound time, which compared to prosumer machines is very short (e.g., 10 seconds or less).
Dan Kehn

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Fullsack

#3: Post by Fullsack »

Agreed. My point was more along the lines of, you can't rely on a bar setting on a pressure gauge to determine pf temp, you need a Scace or equivalent. I think we are both saying the same thing.
LMWDP #017
Kill all my demons and my angels might die too. T. Williams

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HB
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#4: Post by HB »

Sorry, I misunderstood your point. Unless you're concerned about adhering to a standard (e.g., for a competition or calibrating espresso machines in your cafe), I recommend adjusting by taste. With apologies to Greg, for a home barista, I don't think there's much need for a Scace thermofilter. I would not own one were it not for equipment reviews.
Dan Kehn

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cannonfodder
Team HB

#5: Post by cannonfodder »

Nor would I. I usually go by taste then will double check with the Scace. Boiler temperature is more a factor in how much you have to flush and how fast your rebound time. I could hit the same temperature whether my boiler was at 0.8 bar or 1.1 bar, it is simply a matter of timing, shorter flush longer rebound or longer flush and faster rebound. Machine gauges are also inherently inaccurate. You should think of them as a reference point not an absolute measurement. You can make a machine want to favor a particular temperature by tweaking the boiler pressure, but that is more a thermosiphon effect than anything IMHO.
Dave Stephens

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malachi

#6: Post by malachi »

I also don't own one and only really use one (borrowed) when I need to review a machine.

That said, there have been a few times when I could really have used one when diagnosing a problem (as a way of at least eliminating some possible explanations).
"Taste is the only morality." -- John Ruskin

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Fullsack

#7: Post by Fullsack »

Espresso machines I've come across, with the pressurestat set to factory specs. go somewhere north of 204 degrees at the portafilter. If you started with a lower predetermined standard, (set by a Scace), as you do with dosing, and then go higher or lower, as your taste buds dictate, you would save yourself the pain of having to taste a lot of bitter coffee.
LMWDP #017
Kill all my demons and my angels might die too. T. Williams

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HB
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#8: Post by HB »

Fullsack wrote:...you would save yourself the pain of having to taste a lot of bitter coffee.
At one time I would have agreed, but over the years, I have concluded that (a) it's not that difficult to calibrate espresso equipment by taste, and (b) the importance of microadjustments in brew temperature is greatly overstated. That said, if you have a thermofilter handy, by all means, use it.
Dan Kehn