The role of fines and what we really want from a grinder

Grinders are one of the keys to exceptional espresso. Discuss them here.
The_Mighty_Bean

#1: Post by The_Mighty_Bean »

This topic comes to mind as an offshoot of the Spinning for Distribution thread. I'm splitting it, because that thread is more of a practical engineering question, and this one is a question of theory.

As I noted in that thread, according to page 215 of Illy's book, the ideal grind does not consist of particles that are all the same size. Rather, the coarse particles provide a structure that resists water flow allows water flow, which would otherwise be choked by the fines, which release most of the flavor components. (Previous sentence edited 2/7/08 to correct factual errors.)

Illy also talks about a whole range of particle sizes coming out of a given grinding session. What kind of grinders were they using, I wonder?

I don't get it. Maybe this question has a really simple answer. but my layman's understanding was that the most desirable grinders were consistent in the size of the particles they spit out. And indeed, when I look at a photo of Versalab grinds, I see an amazingly even bed.

So if you put Versalab grinds on a screen, can you still shake out a bunch of "fines"? Enough to account for the flavor in the espresso?

Something is just not adding up. Maybe since I haven't read the whole Illy chapter I am missing out on something that they explain. Do they talk about an ideal distribution of particle sizes, by percentage? As in, for a great extraction, we want 55% at 40 micrometers and 35 percent at 229.6 picometers, et cetera ad nauseam et cetera.

~tMb

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TrlstanC

#2: Post by TrlstanC »

The topic of the role of fines actually came up today in this thread Unexpected results when forgetting to tamp.

I sifted out the 14 grams of ground coffee (from a Gaggia MDF), using a cheap kitchen sieve, and I'd guess that almost 2/3 passed through. I wouldn't call everything that passed through fines, some of them were just slightly smaller grinds then what remained, and if I'd gone one click finer on the grind I bet everything would have gone through.

My next experiment is going to be to sift out some coffee and pull shots using the finer pile and one using the coarser pile, I'm just waiting for some fresh coffee to show up. I'd also like to see what people with more precise grinders get in terms of sifting ratios (even though it won't be directly comparable).

The_Mighty_Bean

#3: Post by The_Mighty_Bean »

It is also discussed as part of a Titan Grinder Project SUBTHREAD which is plenty technical, and which I need to go read. Other commenters probably should, as well, so we don't re-invent the wheel.

-bean

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cafeIKE

#4: Post by cafeIKE »

A 10x jeweller's loupe is sufficient to see that NO grinder spits out the same size particle.

Way back, when in the market for a new grinder, I went around to shops asking for "espresso, no water." I'd then examine the grind by spreading on white plastic. What varies is the ratio of "dust to rocks."

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RapidCoffee
Team HB

#5: Post by RapidCoffee »

The_Mighty_Bean wrote:As I noted in that thread, according to page 215 of Illy's book, the ideal grind does not consist of particles that are all the same size. Rather, the coarse particles provide a structure that resists the water flow, and the fines release most of the flavor components. illy also talks about a whole range of particle sizes coming out of a given grinding session. What kind of grinders were they using, I wonder?
I have always assumed it's the other way around: fines control the flow, and the flavor profile is largely determined by the larger particles. To quote of one of my espresso heroes from the Titan Grinder Project:
another_jim wrote:If we can get enough particle sizer time, I'm going to try testing a very simple model:

1. The rate of flow is determined overwhelmingly by the fines -- the more fines, the slower the flow.
2. The extraction of coffee is determined by how fine the average coarse particles are.
3. The quality of grind is determined how narrow the dispersion of the coarse particles is -- the tighter the distribution, the better the taste.
Would you mind typing in the exact quote from the Illy book? Thanks.
John

The_Mighty_Bean

#6: Post by The_Mighty_Bean »

RapidCoffee wrote:Would you mind typing in the exact quote from the Illy book? Thanks.
My pleasure, now that I finally found it again.
An empirical compromise [of particle size distribution] reached by grinder manufacturers resorts to an intermediate distribution...occasionally with a typical bimodality or even trimodality. Such a complex characteristic of particle size is believed to produce a double effect: on the one hand, it forms a coarse fixed structure, which allows the correct flow through the cake; on the other hand, it forms a large quantity of fines of high specific surface, which permit the extraction of a large amount of soluble and emulsifiable material.

Illy, A. and Viani, R.; Espresso Coffee, Second Edition: The Science of Quality. "Percolation", p277.
In Amazon, find the book, go to the Search Within, and type in "distribution and fines".

It's the first search result. Worth clicking the arrow on the right side to read the next few pages, as well.

Also, search "distribution", go to page 2 and click on page 215, and you'll find the same concept briefly mentioned on the bottom of the page.


~tMb

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AndyS

#7: Post by AndyS »

The_Mighty_Bean wrote:the coarse particles provide a structure that resists the water flow, and the fines release most of the flavor components.
I think you got the second part right. But surely Illy means that the coarse particles provide a structure that allows water flow. If the grind was all fines, there would be virtually no flow.
another_jim wrote:If we can get enough particle sizer time, I'm going to try testing a very simple model:

1. The rate of flow is determined overwhelmingly by the fines -- the more fines, the slower the flow.
2. The extraction of coffee is determined by how fine the average coarse particles are.
3. The quality of grind is determined how narrow the dispersion of the coarse particles is -- the tighter the distribution, the better the taste.
1. Again, yes.
2. Average coarse particle? Not sure what that means, exactly. Average in volume, or surface area? John's particle distribution graphs seem to say that the finest one third of the ground coffee mass has nearly three quarters of the total surface area. It would seem that the fines definitely provide most of the extraction.
3. It makes sense that the narrower the dispersion of any group of particles, the more controllable the extraction. But again, the coarse particles probably provide a lot less of the extracted matter than do the fines. And introducing the concept of "better taste" seem to contradict the very apt statement that Jim made elsewhere:
another_jim wrote:I'm not sure "tastiest" is necessarily the thing to go for here. More analytical terms like brightness, bitterness, sweetness, body, aroma, etc may be better.
-AndyS
VST refractometer/filter basket beta tester, no financial interest in the company

Nick

#8: Post by Nick »

AndyS wrote: Average coarse particle? Not sure what that means, exactly. Average in volume, or surface area? John's particle distribution graphs seem to say that the finest one third of the ground coffee mass has nearly three quarters of the total surface area. It would seem that the fines definitely provide most of the extraction.
Don't forget, the fines move downwards. While they do tend (due to increased surface area) to wanna extract faster, you're also sort of tucking those fines down where they're more awash in already-brewed-espresso-extraction than water that wants to dissolve those precious solubles (a.k.a., percolation).
Nick
wreckingballcoffee.com
nickcho.com

The_Mighty_Bean

#9: Post by The_Mighty_Bean »

AndyS wrote: I think you got the second part right. But surely Illy means that the coarse particles provide a structure that allows water flow. If the grind was all fines, there would be virtually no flow.

Yes, thank you. It says that exactly on p215. My mistake, and I'm striking it, above.

So then we have the fines both limiting flow and providing most of the flavor, and forming some sort of structure with just enough coarse particles for what Illy calls "proper extraction" at 277-78. I wonder what Illy defines as a proper extraction- simply a time/volume function? Or do they get into something akin to TDS? More reading to be done.
AndyS wrote:And introducing the concept of "better taste" seem to contradict the very apt statement that Jim made elsewhere
Yes, sorry got sloppy, I meant more controllable taste because one variable would be limited as pre-tamp density approaches a constant. Then we could play with temp and grind to try to adjust the flavor profile, in accordance with descriptors along the lines of what Jim mentioned.

Now where is it we want those fines? The grinder spits them out sort of randomly,- wouldn't it make sort of intuitive sense that we want them as evenly dispersed throughout the basket contents as possible, creating a regular lattice with the coarser grinds? The ideal pattern would work in harmony with the flow properties that Nick just mentioned.

It is just amazing how complicated espresso science can get. Makes me want my next shot to be something strong and alcoholic.

~The brainteased bean

Matthew Brinski

#10: Post by Matthew Brinski »

The_Mighty_Bean wrote: Now where is it we want those fines? The grinder spits them out sort of randomly,- wouldn't it make sort of intuitive sense that we want them as evenly dispersed throughout the basket contents as possible, creating a regular lattice with the coarser grinds?
With reference to current theory of fines migration, I don't believe that is possible. That is unless you develop a whole new type of espresso extraction process... but, then the beverage wouldn't be espresso.

(If you're referring to the "regular lattice" as remaining a constant during the extraction process)


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