drdna wrote:Let me further add this thought ... single dose grinds, in a similar fashion, produce a less uniform grinding

Brilliant. You're predicting that single shot grinding requires a coarser grind setting.

Let me reiterate. You need to grind finer for single dose grinding. Therefore there's

• larger coarse particles
• and/or a more uniform grind
• and/or fewer fines

That is the phenomenon I'm trying to explain.

GC7 wrote:A quick look at cellulose structure shows layers of bonded sugars cross-linked with hydrogen bonds.

Let's not forget that this is charred cellulose. The roasted bean is far more brittle than the green bean. Any idea how much of the original structure survives the roasting process?

RapidCoffee wrote:Let's not forget that this is charred cellulose. The roasted bean is far more brittle than the green bean. Any idea how much of the original structure survives the roasting process?

Not charred but "carefully heated" to induce preferred chemical reactions for best flavor Or we could go to *$.

Your point is well taken. I don't know what survives a roast and I'm not planning on doing any quantitative cellulase enzymatic yields from roasted and fresh bean extract or other measurements to find out. I would guess that brittle and fragile roasted beans do not shear into layers but rather fracture into sizes based on force exerted from many directions as the burrs turn.

I don't think the tissue layers are a single cell thick; the life sized photos of cross section slides in my coffee books show easily visible layers, maybe a half dozen to a dozen, looking like a flower folded in on itself. These could well each consist of several tiers of cross linked cells.

But whatever the micro or meso-structure, burr grinders have a shearing motion. If there's a crowd of beans, it will interfere with individual beans getting flattened by being spread out, and will aid in them getting crushed by compression.

There is no other mechanism that can create the observed facts, since more beans in the burrs at any one time is the only thing that is different.

You describe the basic development of the coffee fruit/bean which is the same as most flowering plants

http://www.coffeeresearch.org/agriculture/beandevel.htm

None of this helps to understand how roasted beans grind using burrs. It also can't explain your theory that the cellulose rich cell wall is differentially ground or fragmented when compared to the inner endoderm or remainder of the embryo or when used as single dose compared with a full hopper weighing down the beans being ground.

Mechanistic details of grinding aside, the only way to decide if there is indeed a taste difference is to do the test in a statistically significant sample size.

I've suggested a real hypothesis about physical grind differences that can be falsified; I'm done.

another_jim wrote:I don't think the tissue layers are a single cell thick; the life sized photos of cross section slides in my coffee books show easily visible layers, maybe a half dozen to a dozen, looking like a flower folded in on itself. These could well each consist of several tiers of cross linked cells.

Jim, could you scan one of these in or point me somewhere I should look? I don't have any coffee books that are as academic as the ones you usually refer to, but I trust they might be available at the library.

I readily found this with a google image search:


Source: Elixir Vitae via Google Image Search

I see a big split in the shape of the bean's cross section, which I assume is the split from the cracking of the beans during roasting, given that the green coffee cross sections I see don't sport this crack--or rather, it's much more subtle . the other layering that I see could just as well be from a fast heating or something like that, just a lighter coloration around the outside. Strange, that seems like the opposite of what I would expect. Overall, the bean looks kinda spongy to me; I am not sure I'm seeing the layering. Still, I wonder about the shard of 'bark' in the SJ sample on the TGP SEM images. Maybe you're totally right, and such shards are more prone to happen with single-dosing. That's kind of been my guess all along (how can bigger particles get through? If they're long/flat, naturally), with no idea of any cell-level mechanism behind it.

Anyway, I'm intrigued by the discussion and eager to read something that could substantiate the idea a little more. Honestly, I think SEM images of single-dosed grinds vs. full-hopper grinds from the same grinder, same batch of beans, and same grind setting would be pretty fascinating and potentially much more enlightening (w.r.t. your theoretical mechanism) than a comparative look at particle distributions of grinders dialed in separately to produce very similar grinds. I'm all for both, but is the former a low-hanging fruit?

Sponge, layers, honeycomb, whatever. Maybe Sivetz, Illy, and Clarke & Vitzthum are all wrong, and coffee is made out of puppy dog tails. I don't care, I used the description of 25 years worth of coffee literature as the bean being layered for the illustration.

The hypothesis itself does not depend on the exact structure of the beans. Burrs counter-rotating will shear the beans, regardless of their composition, and spread them out. If some of the beans are cheek to jowl, they can't spread out, and will get crushed into stacked particles instead. These will pass out of the fixed gap in the burrs stacked, decreasing the coarse particles' average size and increasing their variance. That is what I am hypothesizing. It explains the differences in what people found, and it can be very easily be tested.

Again, does anyone have a different prediction for the compared particle distributions and the mechanism causing the difference?

How many angels can dance on the head of a pin? Is it 6 or 600 or 6000? Does it matter?

This is not the only active thread on this topic of single vs. hopper dosing, and this post is not responding to this thread alone but rather to all of them.

While it might be interesting to try to explain the mechanics behind what happens when one grinds coffee from a partially full hopper vs. using the same grinder in a single dose fashion, the real issue that is discussed related to this is how these two different approaches effect shot quality and reproducibility. An ancillary issue would be coffee waste, to those who care (I am one who does care) and it seems pretty obvious that single dosing will waste a lot of extra coffee, but single dosing proponents know that and it doesn't seem to bother them.

Particle size distributions, although interesting, will not get at the heart of the matter which is whether one compromises taste and/or reproducibility with single shot dosing. If single shot dosing does compromise taste or reproducibility, then particle size distribution might (or might not) explain this result, but in the end the result itself would be of paramount interest, and simply finding differences in particle sizes would not tell you if reproducibility or taste were adversely effected.

There are in essence two things to test; reproducibility, and taste. In order to test them you could do a large series of paired shots using the two techniques. Every shot pair gets included for the analysis of reproducibility, but only the "good" shot pairs are scored for the taste comparison. You might find, for example, that one technique had only 70% as many "good" shots as the other, but that when the good shots were compared there was no difference between them as regards taste. Or, you might find that the good shots from one technique were better than the good shots from the second, however the second technique produced good shots 95% of the time vs. 40% of the time for the first.

Who knows? You'd have to test it to know for sure, and it might turn out that some people would prefer one sort of result over another. The results of such a blinded study would be very interesting, even if they don't have the probability of getting very many people to change their technique.

ken

Ken Fox wrote:While it might be interesting to try to explain the mechanics behind what happens when one grinds coffee from a partially full hopper vs. using the same grinder in a single dose fashion, the real issue that is discussed related to this is how these two different approaches effect shot quality and reproducibility. An ancillary issue would be coffee waste, to those who care (I am one who does care) and it seems pretty obvious that single dosing will waste a lot of extra coffee, but single dosing proponents know that and it doesn't seem to bother them.

[emphasis mine]
I agree with you for the most part, as do I think most of us. I also agree that a mechanism for quantifying reproducibility in addition to just the comparative taste is important. However, I've totally lost you at the bolded comment. It seems like you waste a minimum coffee when you're running pre-weighted, single dosing vs. keeping a hopper full, where you (maybe) have to purge after making grind adjustments, after leaving the grinder to sit idle, etc. Did you switch the two around, or am I missing something key here?