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Computer controlled temp and flow profiling
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jonr
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Joined: 25 Jun 2013
Posts: 298
Location: Americas
Expertise: I like coffee
Posted Tue Oct 1, 2013, 6:10am
Subject: Re: Computer controlled flow
 

The scale (to measure espresso in the cup during brew and allow flow profiling) is working well.   What flow profile is best is a good question.  

Some have suggested (credit to James Hoffmann) as below, but I believe that flow, not pressure is the right variable to control, at least for the last two steps.

- A relatively lower pressure preinfusion period, lasting long enough to soak the cake (5-8s depending on dose).
- A smooth, relatively quick rise to 9 bars over 2-3s.
- A period of 9 bars lasting 7-10s
- A declining pressure in the remaining section, from 9 bars down to 8 or perhaps lower.
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jonr
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Joined: 25 Jun 2013
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Location: Americas
Expertise: I like coffee
Posted Wed Oct 2, 2013, 9:17am
Subject: Re: Computer controlled flow
 

It looks like a steady 9 bars creates a flow profile that is slower in the 0-7 second range, about right in the 7-17 second range and then faster in the 17-25 second range.  This is consistent with my visual observations.  Next step is to try a flatter profile by having the controller reduce pump voltage during the 17-25 second period.
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iko
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Joined: 30 Aug 2013
Posts: 58
Location: Toronto
Expertise: Just starting

Posted Wed Oct 2, 2013, 12:58pm
Subject: Re: Computer controlled boiler temp
 

Is it conceivable that as the water flows through the coffee small particles goes with the flow, and also some of the coffee components dilute making the puck filter less dense, hence the drop in pressure?

Are you aiming for a measurably steady flow? Or a certain flow profile? If so, based on what would you decide on a flow profile?

Interesting. Pressure and flow are directly related (not linearly); meaning, once the coffee is tamped, you can control pump speed only. I guess then you may decide to change the pump speed based on observed flow rather than pressure?
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jonr
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Joined: 25 Jun 2013
Posts: 298
Location: Americas
Expertise: I like coffee
Posted Wed Oct 2, 2013, 2:22pm
Subject: Re: Computer controlled flow
 

Yes, the goal is consistency and better taste.  I find it useful to start with what others have found to work well.  After that, it gets more difficult because I have hundreds of possibilities as compared to most espresso machines with limited controls.
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jonr
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Location: Americas
Expertise: I like coffee
Posted Mon Oct 7, 2013, 6:11am
Subject: Re: Computer controlled flow
 

This is an interesting article that serves as a reminder that pressure profiling, pump power profiling and flow profiling are all related but different things.

Click Here (nickcho.tumblr.com)

So far, flow profiling is giving me great consistency (and taste).
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jonr
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Joined: 25 Jun 2013
Posts: 298
Location: Americas
Expertise: I like coffee
Posted Mon Oct 14, 2013, 2:26pm
Subject: Re: Computer controlled flow
 

It is clear that flow normally increases at the tail end of a shot.  Say the last 5-10 seconds.  Of course with flow profiling, the computer backs off the pump power and keeps flow constant.   I haven't yet tried varying (ie, non flat) flow profiles.

I recommend pre-infusion and flow profiling - small random variations in grind/coffee/humidity/? are at least partially compensated for and you still get a good shot.  And I think that preventing the increase in flow at the tail end of the shot results in better taste.
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jonr
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Location: Americas
Expertise: I like coffee
Posted Sun Nov 24, 2013, 7:23pm
Subject: Re: shot termination
 

I currently terminate a shot based on weight in the cup.  This works well but I am considering terminating a shot based on %TDS (probably estimated from conductivity) in the cup.  Or perhaps using both weight and %TDS to calculate % extraction yield in real-time and stop when it hits a desired value.  Or perhaps by adding a paddle wheel flow meter and comparing water volume pumped (post puck saturation) to weight in the cup (with the difference being coffee extracted).

Some background:  the extraction yield is a major determinant of taste.  Under or over extraction doesn't taste good.  If everything were perfectly consistent, then it wouldn't matter.  Shot after shot, everything would be the same.  Coffee, grind, dose, temps, brew time, brew volume, %TDS, extraction yield, taste, etc.  But of course there are variations and so the question of what to measure to pick the best point to terminate the shot.

Any thoughts?
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andys
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andys
Joined: 10 May 2003
Posts: 856
Location: NY
Expertise: Just starting

Espresso: Speedster, Londinium 1
Grinder: EK-43,Robur, HG One, M3
Vac Pot: Yama
Drip: various
Roaster: PIDed Popper
Posted Sun Nov 24, 2013, 7:47pm
Subject: Re: shot termination
 

jonr Said:

I currently terminate a shot based on weight in the cup.  This works well but I am considering terminating a shot based on %TDS (probably estimated from conductivity) in the cup.  Or perhaps using both weight and %TDS to calculate % extraction yield in real-time and stop when it hits a desired value.  Or perhaps by adding a paddle wheel flow meter and comparing water volume pumped (post puck saturation) to weight in the cup (with the difference being coffee extracted).

Posted November 24, 2013 link

Before you get too far into the conductivity thing you might get a coffee refractometer and a conductivity meter and see how well conductivity meter readings actually correlate to TDS. There is a reason why refractometers have replaced conductivity meters in the specialty coffee industry.

 
-AndyS
picture page:  http://flickr.com/photos/andy_s/sets/
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jonr
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Joined: 25 Jun 2013
Posts: 298
Location: Americas
Expertise: I like coffee
Posted Mon Nov 25, 2013, 8:17am
Subject: Re: shot termination
 

I think that is good advice.  I can't find any data that shows that it does or doesn't correlate (I can probably do without absolute accuracy).   I suppose I could also compare conductivity to oven dried samples.

In looking at a graph of extraction yield, it flattens out near the end of the shot.  So it's probably a bad value to terminate on.  %TDS keeps dropping.
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andys
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andys
Joined: 10 May 2003
Posts: 856
Location: NY
Expertise: Just starting

Espresso: Speedster, Londinium 1
Grinder: EK-43,Robur, HG One, M3
Vac Pot: Yama
Drip: various
Roaster: PIDed Popper
Posted Mon Nov 25, 2013, 4:49pm
Subject: Re: shot termination
 

jonr Said:

I suppose I could also compare conductivity to oven dried samples.

Posted November 25, 2013 link

Yes, but bear in mind that it is dissolved solids that best correlate with taste. Oven dried samples must be filtered to get accurate results. And if you haven't done it, oven drying is tricky. Knowing when to stop is not obvious (the weights keep going lower and lower), and as soon as the samples are removed from the oven they begin absorbing moisture from the air.

jonr Said:

In looking at a graph of extraction yield, it flattens out near the end of the shot.  So it's probably a bad value to terminate on.  %TDS keeps dropping.

Posted November 25, 2013 link

%TDS keeps dropping, yes, but depending on how you pull your shots, it generally doesn't drop so low that it's insignificant.

 
-AndyS
picture page:  http://flickr.com/photos/andy_s/sets/
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