# Brew pressure impact on channelling



## garydyke1 (Mar 9, 2011)

If my understanding is correct with a Vibe pump, if the brew pressure is lower then the flow-rate is higher.

Thus channelling could be reduced with increased pressure?

My machine appears to channel more when set to 8BAR than when set to 11BAR (more efficient fine migration?) although without a SCACE this is all guess work

Anyone else done any research on this?

I want a SCACE real real bad


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## MikeHag (Mar 13, 2011)

Not sure with a vibe pump but with a rotary I've been told recently that I should be aiming for 8.5bar with a filled basket, which tends to be about 7.5 bar with an empty basket. Apparently the lower pressure helps prevent channelling caused by the punch of the water at higher pressure. It also allows you to grind slightly coarser, which prevents fines - which are overextracted - and therefore makes things sweeter. That's how I'm running my machine at the moment, but I've still to reach any conclusions about it other than that I'm generally happier with my shots lately.

Maybe you could try grinding coarser and updosing a bit, Gaz... I know you typically use a 15g backet and it might be worth giving an 18g a try..?


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## garydyke1 (Mar 9, 2011)

In addition to the 15g VST I have a standard HD basket, and, more recently an EP HQ double. I can get 17g-17.5 into both and pours do look better to the eye but not to the palate, really really under-extracted (if sharp and sour is the symptom)

This one coffee that everyone else is raving about is throwing everything into doubt, hence me attacking the brew pressure as a cause for channelling and a bad taste. I ran the Funka 17.5g and purposely ran the shot 40 seconds producing 35g output...as expected bitterness....however that bloody sharpness was still there!


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## MikeHag (Mar 13, 2011)

Temperature ok? If you're running it that long I'd expect a pretty high extraction, so maybe knock it up a degree??


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## fatboyslim (Sep 29, 2011)

Have you tried to re-create the 70 second shot?

Fine for latte art


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## garydyke1 (Mar 9, 2011)

MikeHag said:


> Temperature ok? If you're running it that long I'd expect a pretty high extraction, so maybe knock it up a degree??


I get slight flashing to steam @ 99c on the PID. My PID is 92. Will try 95 for a laugh tomorrow but im nearly out of this coffee now anyway


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## tribs (Feb 21, 2012)

In theory you'll get more channeling at higher pressure and my experiments with changing pressure at OPV on my Classic back this up. My view is with the OPV set at a lower pressure, a lot of the pumps increased flow rate is sent back to the tank via the OPV. The flow into the cup is still the same, once dialled in.

According to Jim Schulman higher pressure leads to increased crema but also more bitters AND sours. Lower pressure to a smoother taste but less crema. I am finding the same, except I seem to struggle to keep the brew temp down with the OPV set at a lower pressure and I am not sure why. Maybe the tendency to channel at higher pressure lead to a generally higher flow rate through the boiler which kept the temperature lower. This should not affect you with your PID machine.

Out of interest have you had any decent brews from the Unk? Maybe its just the beans.


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## garydyke1 (Mar 9, 2011)

These look very interesting , is 90 quid too much to prevent these sleepless nights?

http://www.bellabarista.co.uk/proddetail.asp?prod=314


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## Spazbarista (Dec 6, 2011)

You don't need it.

Get a couple of bags of something conventional that just works and have a play with your OPV and temp settings and note the effect. Don't place faith in roaster's recipes as you've no way of telling if their equipment is accurately calibrated. Calibrate your taste buds instead. Interestingly, I went to the local roastery yesterday and he was telling me that he'd called out the San Remo engineers and they discovered that the temp reading on his brand new machine was way out. They calibrated it correctly, but last night we were testing one of his blends and put the temp up to 94 to try ang reduce the tang. It worked.

FWIW I'd try raising the temp 2 degrees, and then another degree and see what difference that makes. Don't fixate over your PID reading of 92. Mine reads 96, and I don't care what the brew temp is in reality as long as I have that consistent baseline of where most coffees taste good.

I've tried all but one of the Extract espresso blends and frankly none of them poured in a pleasing way. The stuff thins out really quickly. Why? Probably down to how they roast it. IMHO it is ok coffee but not deserving of the hype it gets here. Ill be going there in a few weeks precisely to see what kind of pours they get and how they get them. I'll let you know if I learn anything new.


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## jimbow (Oct 13, 2011)

garydyke1 said:


> These look very interesting , is 90 quid too much to prevent these sleepless nights?
> 
> http://www.bellabarista.co.uk/proddetail.asp?prod=314


I have been wondering about these for a while. It would be good to know more about how they work - do they allow brew water to pass through and do they offer any resistance, where exactly does the temperature probe come out in the portafilter, etc.? Does anyone have one or know more details?


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## garydyke1 (Mar 9, 2011)

My onboard gauge shows 10BAR now with back-flush disk and runs 3BAR when running water through an empty 15g VST.

My notes from Bella B show that 10.5 on gauge = 10 at portafilter = 9.5 when brewing. Thus 10 will now be 9.5 = 9 brewing (if their equipment is accurate!)


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## Spazbarista (Dec 6, 2011)

What would you be worrying about if you didn't have gauges on your machine?


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## MikeHag (Mar 13, 2011)

jimbow said:


> I have been wondering about these for a while. It would be good to know more about how they work - do they allow brew water to pass through and do they offer any resistance, where exactly does the temperature probe come out in the portafilter, etc.? Does anyone have one or know more details?


They have a ball valve so you can set the flow rate/resistance. There's a thread on Home Barista with Schecter, Scace, Schulman, Kehn and that lot discussing it and their view was "don't bother... get a scace". Easy for them to say. Personally I'd have one. Been considering it for a while.


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## garydyke1 (Mar 9, 2011)

MikeHag said:


> They have a ball valve so you can set the flow rate/resistance. There's a thread on Home Barista with Schecter, Scace, Schulman, Kehn and that lot discussing it and their view was "don't bother... get a scace". Easy for them to say. Personally I'd have one. Been considering it for a while.


Get 4 people to chip in , split the cost and pass it round like a coffeeforums olympic-espresso-baton !


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