Posted Fri Jun 22, 2012, 8:34am Subject: Dosing as a function of height (D = f(x))
I'm a longtime reader, first time poster -- currently honeymooning with my Breville Dual Boiler, and it has been a blast. My current weakness, however, seems to be dosing. To get the portafilter in, I have to push pretty hard (sidebar: can I hurt/damage my machine like this? I don't want to treat her too rough). Roughly how far down from the lip of the portafilter should the coffee puck stop after a solid 30 - 35 lbs tamp? I find my best shots/cleanest pucks come when I can see the indentation of the group head screen -- but is that a bad sign?
Well, that depends if you see it on the dry puck (before extraction) or the wet puck (after extraction). according to the rules of how to produce the best coffee, the coffee in the PF should not touch the screen when first inserted, but after getting wet, the coffee in the PF expends then it should touch it.
I guess the reason behind this rule is that when the dry coffee (very small particles) touches the screen, it gets inside the screen holes and blocks them so you do not get the proper flow. after the coffee expends when gets wet, the particles are larger and do not block it. In the opposite case, if when getting wet the puck is distant from the screen, the pressure can start to "lift" layers of coffee from the puck and cause channeling.
hope i got it right... any other thoughts are welcome.
emradguy Senior Member Joined: 31 Mar 2011 Posts: 3,681 Location: Houston Expertise: I live coffee
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Posted Fri Jun 22, 2012, 2:09pm Subject: Re: Dosing as a function of height (D = f(x))
some people use a "nickel test" to assess where their (dry) puck should be after tamping. To do this, you fill your pf and tamp as normal. then place a nickel in the center of the puck and engage the pf on the group. don't pull the shot yet, but just take the pf back off the group still dry. carefully remove the nickel without disturbing the puck. there should be only a slight indentation.
that's one method of adjusting dose and a good general guideline to start with. you can modify from there by altering grind setting.
whatever you do, remember that the taste in the cup is the most important part.
will you hurt your machine by overdosing, probably not. if you're having trouble because of too high a dose, it's likely that you're merely fighting the grounds to get the pf to engage. your grind fineness is going to play more of a role than dose in whether you choke the machine or not.
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tracerbullet Senior Member Joined: 13 Feb 2012 Posts: 168 Location: Saint Paul Expertise: I love coffee
Posted Mon Jun 25, 2012, 11:58am Subject: Re: Dosing as a function of height (D = f(x))
I will say from having fixed machines for people and refurbbing others as a sort of hobby - if you overdose as a habit and hit that screen, you will want to periodically take the screen off and clean it and everything under it thoroughly. I've seen machines that didn't flow water for no reason other than the screen was plugged with grinds - rotten moldy looking grinds by the way.
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