# Cherub. To flush or not to flush, that is the question.



## cold war kid (Mar 12, 2010)

Evening and happy Friday.

I'm saving for a new espresso machine and quite fancy a hx as they're usually a little cheaper and smaller than dual boilers. The cherub is the one I'm thinking of as it's the east expensive one that I like the look of. Aesthetics are quite important to me, and yes, I know that makes me a little bit shallow but at least I'm honest.







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There is however one thing I d like clearing up.

From what I've read the cooling flush is useful for controlling the brew temp but I've read in a couple of places that the Cherub doesn't need a cooling flush. Is this true? Assuming it is, how would I go about playing around with brew temps? I know the obvious answer to some would be to get a double boiler with PID but it all seems a bit sterile to me and anyway it would take forever to save for even something as bottom end as a brewtus and without really searching I know of a couple of retailers off the top of my head that would deliver a cherub to my door for £750 or less.


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## h1udd (Sep 1, 2015)

Well if it's an hx it will need a cooling flush as the water sat waiting in the pipe behind the group head will be above the temperature ideal for your shot, so it's good to clear this. ... All you need is a few seconds of flush to get the temps back to normal

regarding brew temp, you can raise or lower it by upping or lowering the pstat - a lower pressure will produce less steam and a lower temp shot.


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## cold war kid (Mar 12, 2010)

h1udd said:


> Well if it's an hx it will need a cooling flush as the water sat waiting in the pipe behind the group head will be above the temperature ideal for your shot, so it's good to clear this..


That was my understanding of how these things work. I can't see how any hx could be different as they all have a tube of some sort running through steam. Surely eventually that water will get red hot no matter what. I have read it a couple of times though.

Do you own a cherub? Does it steam at the beginning of your flush?


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## jlarkin (Apr 26, 2015)

Don't know about the cherub but some of them have a way to manage the temperature. Could be wrong but I think it was a thermosyohon. If it's got an E61 group you could consider getting an Eric's thermometer.

Also home Barista has some good information on cooling flushes and techniques.


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## GlennV (Mar 29, 2013)

It's perfectly possible to design/tune an HX machine to require little, or even no, flushing. Most notably, Nuova Simonelli did it for the Aurelia which was used at WBC. The idea is to restrict the thermosiphon so that the group runs cold. For the first shot from idle the superheated water in the HX is cooled by the group. For subsequent shots the group will be warmer and water in the HX cooler, balancing out to roughly the same temperature if everything is properly designed. I too have seen it claimed that the Fracino machines behave like this, but have no experience. I do know that they have a horizontal heat exchanger, which is not the most efficient (maybe deliberately so).


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## h1udd (Sep 1, 2015)

No, I have an hx izzo vivi. But in therory it's should work the same


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## DavecUK (Aug 6, 2013)

GlennV said:


> It's perfectly possible to design/tune an HX machine to require little, or even no, flushing. Most notably, Nuova Simonelli did it for the Aurelia which was used at WBC. The idea is to restrict the thermosiphon so that the group runs cold. For the first shot from idle the superheated water in the HX is cooled by the group. For subsequent shots the group will be warmer and water in the HX cooler, balancing out to roughly the same temperature if everything is properly designed. I too have seen it claimed that the Fracino machines behave like this, but have no experience. I do know that they have a horizontal heat exchanger, which is not the most efficient (maybe deliberately so).


The Aurelia II used for the WBC 2012-2014, has twin boilers and a thermostatically controlled group.

http://www.nuovasimonelli.it/images/stories/site/prodotti/tradizionali/brochure/AureliaII/hydraulicplan-aureliaii-t3s-20131008.PDF

The Aurelia is more like the traditional HX, but used between 2009 - 2011 for WBC comps. it also had nothing particularly special about it.

The reason large machines (commercial) don't usually require much in the way of flushing is their boilers are so large they can be run at lower temperatures than domestic machines and still give good steam power. this helps to reduce the flushing required, it also means HX recovery issues are not such a problem. Smaller domestic machines have to run the boiler much hotter to be able to maintain steam power. Many Fracino machines do use brute force to allow lower boiler temperatures to be used. I had a Heavenly with a 2 litre boiler and 2.8 litre heating element. This design strategy allowed for the use of lower steam boiler pressures/temperatures and hence less flushing. The 2.8 kW heating element being easily able to maintain steam pressure.

Domestic HX units are a compromise and if a machine required NO flushing, then it's unlikely to be thermally stable within the shot, unless some real trickery with mixer valves was used and I've not seen this yet. I have investigated them, but so far there is nothing that would actually work well at this time.

I have toyed with a design of HX that would allow the user to change brew temperatures (like a dual boiler can), run a hot steam boiler, but not affect the shot and require no flushing. However I cannot discuss it further, because it has not been patented and if I take it further...it might need to be. Any disclosure of the design here would make any patent invalid.


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## badger28 (Jan 5, 2013)

I contacted fracino a while ago regarding this. They said that the cherub doesn't need a cooling flush due to the design. However they usually flush for a second or two when making an espresso themselves.

Not actually done any tests myself and took fracino at their word...


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## urbanbumpkin (Jan 30, 2013)

badger28 said:


> I contacted fracino a while ago regarding this. They said that the cherub doesn't need a cooling flush due to the design. However they usually flush for a second or two when making an espresso themselves.
> 
> Not actually done any tests myself and took fracino at their word...


That's interesting, although I can't work out how a HX wouldn't need a cooling flush.


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## badger28 (Jan 5, 2013)

I didn't press to get any further details, maybe I should have done!

I seem to recall that someone has said that the group head design of the cherub means that a cooling flush is less critical. However I just cannot remember why!


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## DripDrop (Sep 11, 2015)

Londonarium blog claims that the Cherub does not need a cooling flush.

Having said that it describes the group as e61 which is not, technically, true because of the lack of manual paddle so maybe a tiny pinch of salt on that.


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## gwapenut (Nov 5, 2011)

I bung a couple of seconds worth of water into my cup anyway, because it gets rid of any residual old grinds stuck to the screen, and helps the cup warm up a little. Any cooling that occurs is a third benefit.


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## cold war kid (Mar 12, 2010)

Thanks for the replies so far.


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## MediumRoastSteam (Jul 7, 2015)

Having owned an HX machine before, I would highly recommend you to try the machine before you buy it if you can. I found that, on mine, a Rocket Evo2, if I left idle for over 30 mins it would require a cooling flush, but if left for 25-27 mins it wouldn't. Saying that, every day the coffee tasted different, making me thinking sometimes "I wonder what that temperature was". So, in order to get consistency, you may have no option but to perform a cooling flush. Also, the Cherub has a relatively larger footprint if compared to a Rocket Cellini or an Expobar Leva. Maybe someone who actually owns a Cherub can chime in here. Alternatively, I don't even know if this is possible, could you make an appointment with Fracino and check the Cherub "on the job" before buying it?


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