# Perger on Grinding (Latest barista hustle)



## risky (May 11, 2015)

http://www.baristahustle.com/grindingthoughts/

He wants some debate!


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## insatiableOne (Jul 29, 2015)

Subscribed


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## hotmetal (Oct 31, 2013)

An interesting read as always. And I lost the rest of my evening reading all the ones I'd missed in between times! Not sure I'm qualified to debate with MP though. Plus he doesn't approve of my convex Goldfinger ?


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## insatiableOne (Jul 29, 2015)

Meh..many argue that flat is the only way.

I will witness a slight flavor change between bottoms. My last years supply does not favor the curved bottom. Although I will state the last three different Ethiopian naturals I just roasted sure did. All of different varietals.


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## hotmetal (Oct 31, 2013)

Well I'll be honest and say that I don't really notice a flavour change between the flat 58.35 and my convex 58.4. The convex Torr is heavier and lovely to use. The flat gives you maybe a more positive feeling of what the bed is doing underneath. I've yet to have an obviously uneven extraction with the Torr, although I haven't had it long. I think Perger's point is that the puck should be flat in order for an even extraction to happen but there's a theory behind convex too and in practice I think both work well. Convex seems to seal the edges well, provides less precise feedback but is more forgiving. It doesn't seem to like 'polishing' as easily as the flat (which MP now advises against anyway). Both bases are working for me.


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## MWJB (Feb 28, 2012)

There have been a few tests of flat vs convex now, all are in agreement that non flat tampers give lower extractions.

I think it's nutating that Perger advises against now, rather than polishing in the "10 questions" video the St Ali staff do about a quarter turn?


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## hotmetal (Oct 31, 2013)

Oh that's interesting about flat vs convex - hadn't seen that. Can't say I've noticed much taste difference either way so I'm guessing that although it's deemed conclusive it's fairly marginal? Then again a fair number of my shots get made into flat whites or cappuccini so I probably won't notice unless trying straight espresso back to back. I think MP advises against polishing purely on the basis that you might in some way 'unflatten' the bed in the process, and that polishing allegedly makes no difference.


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## MWJB (Feb 28, 2012)

Indeed, I doubt polishing makes a difference to extraction (assuming the puck is not disturbed), but it does leave less grinds stuck to the tamper.


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## jeebsy (May 5, 2013)

MWJB said:


> There have been a few tests of flat vs convex now, all are in agreement that non flat tampers give lower extractions.
> 
> I think it's nutating that Perger advises against now, rather than polishing in the "10 questions" video the St Ali staff do about a quarter turn?


I don't polish loads but a 1/4 or 1/2 turn helps to dislodge any grounds that might have got stuck in the between the basket and the tamper. Makes pulling out smoother.


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## Mrboots2u (May 10, 2013)

MWJB said:


> Indeed, I doubt polishing makes a difference to extraction (assuming the puck is not disturbed), but it does leave less grinds stuck to the tamper.


Depends how you polish









Ive seen people apply a lot of pressure when doing this for instance and the thinking was that an extra step - " polishing was another step that could lead to inconsistency. Whether it leads to any difference extraction wise or not , dunno ..

I have stopped polishing and made sure i lift the tamper out pretty slow , but this is a home baristas technique and I'm sure that it i was serving on bar , my seed would need to be alto quicker for service


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## dsc (Jun 7, 2013)

I myself wonder where the whole ~0.05mm misalignment statement came from. Would love to see some testing and test protocole behind this.

T.


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## risky (May 11, 2015)

dsc said:


> I myself wonder where the whole ~0.05mm misalignment statement came from. Would love to see some testing and test protocole behind this.
> 
> T.


Indeed. Sometimes these stated errors seem as if they would surely be outweighed by the lack of uniformity in the beans being ground? I've never seen any data from testing to do with burr alignment.

Maybe @Terranova can shed some light on this?


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## dsc (Jun 7, 2013)

What do you mean by lack of uniformity in the beans risky?

T.


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## risky (May 11, 2015)

dsc said:


> What do you mean by lack of uniformity in the beans risky?
> 
> T.


Well beans are not all the same size and shape, so no two beans would break apart exactly the same etc. I don't know if that actually makes any difference. As with many things in grinding there seems to be a lot of conjecture and not a lot of facts with data to back it up.


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## MWJB (Feb 28, 2012)

risky said:


> Well beans are not all the same size and shape, so no two beans would break apart exactly the same etc. I don't know if that actually makes any difference. As with many things in grinding there seems to be a lot of conjecture and not a lot of facts with data to back it up.


This may be true...then again it may not (I have no idea either). But it strikes me that it would probably be more of an issue if we were coarsely chopping up 2 beans, but for espresso we might actually be chopping each gram of beans into the region of 28,000 particles (MPE Chicago)...x20 for a typical dose. So with each half a million particles per dose we are perhaps more concerned with trends, than with assessing the specific differences between each particle, or % to several decimal places.

The fact that shots can be reasonably repeated might suggest that we are largely getting away with the bean to bean difference?

That said, it would be interesting to see the impact of certain degrees of misalignment, 50microns difference could be enough? Especially if targeting grinds in the 200-250micron median range?


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## dsc (Jun 7, 2013)

Well apparently there is no data to back this up:

http://www.baristahustle.com/grindingthoughts/#comment-2452757080

I'm well against quoting random small numbers, this is how coffee myths are created.

T.


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## risky (May 11, 2015)

The guy is his own worst enemy sometimes. He claims to hate coffee myths but then propagates new ones.


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## jlarkin (Apr 26, 2015)

To be fair the very first paragraph says:

"There's a number of various grinding-related thoughts rolling around my head at the moment. They're not fully formed (and possibly red-herrings, so look out!) but I thought I should put them out there. I don't have any data to back them up, and I'm even sure they're all true."

I take that to be "not even sure" but a mistake...


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## dsc (Jun 7, 2013)

Crap indeed, should've read the whole article I guess still if you are quoting numbers I'd say don't make it up, otherwise it's just a meaningless discussion.

T.


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## jlarkin (Apr 26, 2015)

dsc said:


> Crap indeed, should've read the whole article I guess still if you are quoting numbers I'd say don't make it up, otherwise it's just a meaningless discussion.
> 
> T.


Yes I tend to agree, but I guess he's trying to stoke a bit of discussion for the site and maybe he was short on time . My other idea, maybe he's trying to see how easily things become "coffee myth" with no data and no actual backing to say it's true by the person that suggested it? Probably not tho


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## dsc (Jun 7, 2013)

Coming from an engineering background I dislike when numbers are thrown around without any data to back them up. I also don't like the argument behind doing so, if someone doesn't know much about machining tolerances, 0.05mm is not going to tell them much anyway, so a generic statement about very tight alignment required would've been enough.

T.


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## risky (May 11, 2015)

jlarkin said:


> Yes I tend to agree, but I guess he's trying to stoke a bit of discussion for the site and maybe he was short on time . My other idea, maybe he's trying to see how easily things become "coffee myth" with no data and no actual backing to say it's true by the person that suggested it? Probably not tho


Imagine it was all a ruse, and he had concrete data to prove that alignment is meaningless and just wanted to see if he could spread false info and how easily it would be accepted as gospel for he is the mighty PERGATRON.


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## hotmetal (Oct 31, 2013)

I think he's committed *Pergery * in the eyes of the coffee jury.

Coat. Door. Gone!


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## MWJB (Feb 28, 2012)

I think it's reasonable enough to suggest a 50um shift in median grind (& resultant impact in oversize particles) can have an impact, this was implied in the grinder comparison. The question really is what degree of misalignment does it take to cause this & how much does it vary by grinder design?...Oh, and what can we realistically do about it?


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## hotmetal (Oct 31, 2013)

Yes I do think we like to tilt at windmills sometimes! Worrying about 50 Mike when ultimately all grinders will have some variance and tolerances. We'll still end up buying whatever the forum consensus tells us is the best at our budget.


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