# Screen mark?



## Beemer (Jun 19, 2012)

I have read that if a screen mark is visible then too much ground has been put in the basket. Does this statement apply to post tamped or just post pulled? I do get a light mark from the screen rim but only post pull.


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## funinacup (Aug 30, 2010)

That's normal. The ground coffee will expand when it infuses with water and touch the screen slightly.

If the coffee touches the screen before you've started brewing then your basket is probably at max capacity and you should select a size up.

Michael

Fun in a Cup Coffee Training


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## chimpsinties (Jun 13, 2011)

I suppose this worry comes from if you put too much coffee in, then if it touches the screen when you put the PF in the machine it risks cracking the puck. Thus you'll probably get a gusher.

On the other hand if water has hit your puck and it's expanded which has caused marks in the top but not compromised the pucks integrity then it's ok.

It's a hard one to judge because you'd have to put the PF in the machine then take it out again to see if it's being broken up even before water hits it. This in itself will probably make that puck unusable so you'd have to redo it anyway.

In answer to your question, I'd say if it's there post tamp, then you're risking trouble (but not necessarily going to get a bad pour, just if it did break the puck), if it's there post pull then don't worry about it.

just my 2p


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## forzajuve (Feb 2, 2011)

Your tamper should be able to ensure that you have enough space between grounds and screen. Provided the top of the tamper base sits level with the top of the basket you will have enough room.


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## chimpsinties (Jun 13, 2011)

That's not a very good guide to be honest. My Rocket tamper for example is mahoooosive. It's probably 1.5cm-2cm deep. If I was to press it all the way down there'd be no room for coffee


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## RobD (May 2, 2012)

i used ridged baskets and find that the top of the ridge feature is a good guide to giving enough space in the portafilter for the screen, but from looking at the specs of a few different machines, the screen does differ in depth from the seal,

the easiest way would be to get a vernier and measure the distance from the PF seal to the screen and add a few mm to give the puck room to expand. on my Expobar its 8.88mm from seal to screen and both my Happy donkey & Knock tampers are 10.8mm deep to the rad on the chamfer so not a bad guide,


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## Beemer (Jun 19, 2012)

RobD said:


> i used ridged baskets and find that the top of the ridge feature is a good guide to giving enough space in the portafilter for the screen, but from looking at the specs of a few different machines, the screen does differ in depth from the seal,
> 
> the easiest way would be to get a vernier and measure the distance from the PF seal to the screen and add a few mm to give the puck room to expand. on my Expobar its 8.88mm from seal to screen and both my Happy donkey & Knock tampers are 10.8mm deep to the rad on the chamfer so not a bad guide,


Is a ridged basket the same as the ridge I have in mine which is for the Portafilter spring to engage?


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## JamesG (Mar 29, 2012)

You can measure the headspace by putting a coin on top of the puck. Lock it in and then unlock it (without brewing) and see if its left an impression.

There's an interesting post on headspace and its affect on consistency here: http://www.koreanbarista.com/post/28001032988/watch-your-head-space?2cec9f80


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## RobD (May 2, 2012)

Beemer said:


> Is a ridged basket the same as the ridge I have in mine which is for the Portafilter spring to engage?


Hi Beemer, yet that it, i was wrong in saying that its the top of that feature i use, more like the bottom but they can differ from machine to machine a little, best to measure it and the screen depth but i use around 10mm as a rough guide.


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## Beemer (Jun 19, 2012)

JamesG said:


> You can measure the headspace by putting a coin on top of the puck. Lock it in and then unlock it (without brewing) and see if its left an impression.
> 
> There's an interesting post on headspace and its affect on consistency here: http://www.koreanbarista.com/post/28001032988/watch-your-head-space?2cec9f80


Now that was a very interesting read! His comments after he assessed his data appear logical. I had read elsewhere that increasing the pressure does not reduce the pour speed linearly and his comment about Darcy's law might be the reason.

Anyhow I'm going to ensure that space is left under my screen for the "perfume spray effect". That said I wonder if anyone has been able to make a clear grouphead that allows examination of coffee flow out of a screen?


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