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

[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

[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]

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

[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."

[RapidCoffee]

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:

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.

[The_Mighty_Bean]

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

[AndyS]

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.

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:

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.

[Nick]

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).

[The_Mighty_Bean]

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.

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]

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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[The_Mighty_Bean]

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


.

No, I mean at the beginning. To produce the most even extraction possible.

[AndyS]

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).

It's certainly a complicated scenario. What does your (true) observation above say about the results of the extraction?

[darrensandford]

This makes me want to brew a shot, then dry the puck, then slice it into layers, crumble it and then see how many fines are in each layer

[Matthew Brinski]

No, I mean at the beginning. To produce the most even extraction possible.

Ok, but fines tend to shift from their initial positions in the coffee cake once brew water is introduced. So, I don't think that it would make a significant difference if they were equally organized throughout the coffee cake matrix prior to brewing.


.

[AndyS]

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?

One of the supposed advantages of dosered grinders vs doserless grinders is that the doser tends to keep things mixed up better -- especially when the barista does the rapid clonk-clonk-clonk-clonk with the doser handle as the shot is ground.

[barry]

This makes me want to brew a shot, then dry the puck, then slice it into layers, crumble it and then see how many fines are in each layer

Just don't use a machine which has a brew solenoid.

[barry]

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?

Wouldn't it make even more intuitive sense that the fines are NOT spit out randomly by the grinder, but in the "natural distribution" associated with grinding coffee?



I'm still trying to reconcile your quest for "even distribution" and your desire to shake a puck down to maximum density (which will congregate fines towards the bottom).

[The_Mighty_Bean]

Wouldn't it make even more intuitive sense that the fines are NOT spit out randomly by the grinder, but in the "natural distribution" associated with grinding coffee?



I'm still trying to reconcile your quest for "even distribution" and your desire to shake a puck down to maximum density (which will congregate fines towards the bottom).

Sorry folks, I'm very slow in responding to these threads, with the bar exam under 2 weeks away. I'll respond to a number of comments once that form of medieval torture is over with.

Barry, just a quick answer- I'm not sure what "natural distribution" is, but I trust it to be desirable about as much as I trust "natural law". I think the way a grinder mixes the grounds during the grinding process is going to be unique to that make and model, and I'm not at all sure that grinder engineers have thought to optimize that blending process.

When I call it a blending process I am just referring to that "natural" mixing- not any sort of homogenization. It will differ depending on lots of variables including burr shape, burr size, length of path to the basket, presence of a doser, et cetera.

So, to answe your first question more directly, there may be so many variables involved that the lattice structure of the grounds -as spit out- will always be essentially random.


The question I have evolved into asking is, is there an ideal distribution and lattice structure of particle sizes, pre-tamp?

Do we want that sort of distribution homogenized so that, before the water hits, the particles start out close to an even lattice of larger and smalller particles? I am no longer at all certain that we want the fines to migrate towards the bottom before the water even arrives.

In other words, no need to reconcile the quest for even distribution with shaking the fines to the bottom. That's why I spun off this thread from the other one-- the question in this thread is where do we want those fines to go during the distribution process, and should we even care?

~tMb

[Jasonian]

I wish the new feature on Coffeed were available at the time, but this very topic was discussed at much detail about a year or so ago. (maybe less time, but that "feels" about right)

I tried searching but couldn't find it. If I do, I'll report back.



I feel the need to inject the notion that the coffee particles aren't randomly shaped. They are ribbon slices.

Such a shape offers a much higher surface area than otherwise thought. I don't think you can prevent the larger particles from extracting while the smaller particles extract.

I don't believe it is one or the other responsible for the bulk of the espresso's flavor. Surely, there are more than merely two grind sizes at work here. "fines" and "large" and everything in between are more likely to be found.

The question, is what is the "ideal" variance?

Do fines migrate? Sure! but how much?

Well, just the WDT is enough for me to notice a visual difference in extraction color, so I'd imagine a bit more than intuition suspects, but less than many seem to give credit to.


Just food for thought.

[fac10]

I recently ran across this article which may be of interest to those following this thread. The most interesting point being that some high-end industrial grinders are capable of generating 'bimodal' grinds, where the particle size distribution has two separate medians. Apparently this has some beneficial effects, at least with respect to the manufacture of espresso pods. Presumably, a cruder version of this effect could be achieved by mixing the output of grinders at two separate settings.

Perhaps the blended bimodal grind will be the next bleeding edge in the search for the perfect extraction.