# The effect of bean origin and temperature on grinding roasted coffee



## bronc (Dec 10, 2012)

The long awaited paper just came out: http://www.nature.com/articles/srep24483

tl;dr: Flash freeze your coffee beans with liquid nitrogen before grinding to achieve a higher and more even extraction.


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## SmithStCoffeeRoasters (Feb 23, 2016)

Interesting read... would some type of cooling system in the hopper be a practice application of the study


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## Missy (Mar 9, 2016)

bronc said:


> Flash freeze your coffee beans with liquid nitrogen before grinding to achieve a higher and more even extraction.


Dammit I just used the last of my liquid nitrogen freeze-raying my enemies.


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## h1udd (Sep 1, 2015)

Make icecream with it and you won't have any enemies


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## Missy (Mar 9, 2016)

@bronc call me lazy I skimmed to the conclusion. Why flash freezing over just getting them out of the freezer when required? Was that risk of water fracturing the beans?


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## bronc (Dec 10, 2012)

Probably yes. Flash freezing creates small crystals while the regular one large crystals.

edit: if i remember correctly, freezing them in the freezer still improves grind distribution. Actually the biggest difference is between room temperature and -19*C.


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## jlarkin (Apr 26, 2015)

hat tip to @Xpenno for the photos of the burrs


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## joshuadaniels (Apr 18, 2016)

That's awesome! If they are frozen it does improve grind distribution. Good article.


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## GlennV (Mar 29, 2013)

It doesn't really show that. They show "that grinding cold results in a narrower particle size distribution, and reduced mean particle size". Note though that this is a statement about the unweighted size distribution, which is dominated by the smallest of fines as these are present in very large numbers. They could have left half the beans unground without changing the results (ie the mean particle size and the width of the particle size distribution would be essentially unchanged) but I think most people would call that an inferior grind distribution.


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## MWJB (Feb 28, 2012)

It is unusual that they have not also included distribution curves by % volume/density of particle size.


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## bronc (Dec 10, 2012)

@MWJB @GlennV

Not sure if follow Barista Hustle on Slack but there is a long discussion on the paper, especially the volume/mass thing.


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## MWJB (Feb 28, 2012)

bronc said:


> @MWJB @GlennV
> 
> Not sure if follow Barista Hustle on Slack but there is a long discussion on the paper, especially the volume/mass thing.


No I don't, can you summarise?


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## bronc (Dec 10, 2012)

Nope, didn't understand a thing


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## MWJB (Feb 28, 2012)

bronc said:


> Nope, didn't understand a thing


Valuable insights then ;-)


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## bronc (Dec 10, 2012)

Too sciency for me. The tl;dr is that we need completely new grinding machinery that might not be a grinder at all - maybe lasers making the beans fracture in same size particles? Yup..


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## jlarkin (Apr 26, 2015)

I don't know if this is news to anybody but Chris said the EK grind has 72% ish of the surface area coming from fines (fines being below 125um or so). Somebody asked is there a reason that a Volume % graph of the data was omitted - Chris said because it's useless. Then he provided an excel file of the room temperature data (I can't access the slack on my computer so I haven't looked at it). Their was other discussion but I haven't gone through it yet. It's likely that I don't know enough about it, to know which bits would be the most interesting.


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## MWJB (Feb 28, 2012)

If they're 72% of the most critical aspect driving extraction, then their probably not "fines". I'm not aware (that doesn't mean it isn't happening) of people brewing espresso with particles above 100um exclusively, which would suggest that they are a necessary component.

Is there an experiment that we have missed that says that particle size by volume is irrelevant?

Extraction is a mass exercise, *if* (I don't know for sure) particles under 70um make up, say, 5% of the mass of the dose, they can't be responsible for 72%-ish of the extraction.

Surface area has no mass. To extract the particles water needs to access the particle, if the density of very fine particles is too great, that might not happen. This would seem to be born out by falling extraction yields if grinding too fine and the fact that you can choke machines, or get edge channelling where water cannot pass evenly through the puck?

In Hemro/Perger's previous grinder test, all the grinders tested made a bimodal grind, but the difference in extraction seemed more related to overall tightness of distribution (particles over 100um)?


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## GlennV (Mar 29, 2013)

Yes indeed, you can't make coffee out of surface area.

Let me make my example more concrete. For Sample A take 20g of espresso grind, for Sample B take 10g of the same espresso grind and add to it the large particles (over 0.5mm say) that result from hitting another 10g of whole beans a few times with a hammer. By the measures they are using in this paper, based on particle distribution by number, sample A and sample B would have the same distribution. If the mean particle size is around 10 micron, as they show, then each bean produces hundreds of millions of particles - there simply won't be enough of the larger particles in Sample B to register on the graph.


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## SmithStCoffeeRoasters (Feb 23, 2016)

Matts user friendly summery of the paper

http://www.baristahustle.com/grinder-paper-explained/


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