The meaning and consequences of 'False Pressure'

[sophiecentaur]

I like good espresso coffee and I've owned and used a Pavoni Europiccola lever machine for ages. Not surprisingly there are fora and Facebook groups all over the place, containing all levels of 'knowledge' about science and coffee making.

There are two criteria which affect the coffee: temperature of the water and pressure of the water being forced through the grounds (set by the force on the lever, its length and the area of the piston). Also, to get good foam, the boiler pressure needs to be appropriate.

The machine has a pressurised boiler with an electrical element and a 'pressurestat', which can be set to a pressure of choice. The recommendation is to purge air from the boiler through the steam pipe (for frothing) to get the correct temperature of the water. It figures that the more air there is in the boiler, the lower will be the partial pressure of the steam and the lower will be the temperature of the water. Hence the use of the term 'false pressure'. I have googled this term and pretty much the only responses I get are from coffee nerds (me too sir).

So - why not use a thermostat, if you want an appropriate temperature? I would be very surprised if there are no other coffee aficionados in PF so what's the proper, informed, opinion of the topic?

 

[anorlunda]

It sounds akin to audiophile jargon.

I'm happy with instant coffee.

 

[sophiecentaur]

It sounds akin to audiophile jargon.

I'm happy with instant coffee.

There is a lot of BS about Espresso (in particular) Coffee but it's like baking your own bread and general self preparation of food. All I can say is that a lot of people are seriously missing out on good coffee etc. experiences. Instants vary from disgusting to 'nothing like coffee' for me. But it's my fault for taking an interest in it for a start. Pouring hot water from a kettle onto some granules is certainly quick - but why not just have hot water? (Or a good Tea like Assam).
I have a running mock battle with my lovely daughter in law about taking sugar in hot drinks. She says that I imply sugar is diminishing her intellectual powers - as if I could ever, in her case.

But - about this false pressure (water not social).

 

[JT Smith]

I'm no expert but I do know that there are different types of espresso machines and you can find pressurestats, thermostats, and PIDs in their boilers. From what I just read after a brief search, pressurestats provide better adjustability and a tighter deadband than thermostats.

I've also encountered the term "false pressure" in the context of espresso. AFAIK that's the only place that particular terminology is used. It's not hard to find examples of poorly coined terminology, not just in coffee. Scientists do it too.

 

[hutchphd]

So - why not use a thermostat, if you want an appropriate temperature?

Surely there is limit thermostat on the heater on the Pavoni. So I guess I don't understand your question. Is this related to "crema" ?

I am however in total agreement with your coffee sentiments. I do most enjoy a morning Cappucino with a shaving of dark chocolate and just a sprinkle of cinnamon sugar. I have a 15 bar capresso EC100 machine that is very good I think. Although not quite the Piazza del Popolo...

 

[Lnewqban]

Please, see:
https://www.engineeringtoolbox.com/steam-air-mixture-d_427.html

 

[sophiecentaur]

It's not hard to find examples of poorly coined terminology, not just in coffee. Scientists do it too.

Ain't dat the truth?

Please, see:
https://www.engineeringtoolbox.com/steam-air-mixture-d_427.html

Ah yes. The graph in the reference implies that 15% of air in the boiler would depress the temperature by about 5C with a gauge pressure of 1Bar. That would be quite important to the taste of the coffee, according to the enthusiasts. Purging the air would definitely give more consistent results.

Up till now, I have questioned the need for knowing boiler temperature but one thing it would tell you is how much air is in there. In some old Europiccola designs, there is the possibility for steam to get into the 'group head'. That can reduce the effective volume of water forced through the coffee grounds (small shots) and any included air can cause sponginess in the pull and 'sneezing' when removing the portafilter.
You learn something every day.