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Grind Sifting for Brewed Coffee - Page 3

Postby RapidCoffee on Tue Dec 29, 2009 12:55 am

CRCasey wrote:But when you have to go to a fractional wavelength of a absorption pattern of light don't you think that a size that small really is not that useful in fluids like this. That is not what we want to measure for. You can pick a standard and work with it. A Micron standard may be overkill for this.

I have no idea what you mean by this. The shortest wavelength of visible light is roughly 400 nanometers, about 1000X smaller than the diameter of espresso grinds (and 100X smaller than the fines).

The only thing that makes grid sizing confusing, is the contribution of the wires in the mesh. Otherwise it would just be the distance (e.g., one inch) divided by the number of openings (e.g., 30).
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Postby CRCasey on Tue Dec 29, 2009 1:00 am

I was talking about a standard way of measuring. But I have to say that your reply lost me as much as mine did you.

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Postby RapidCoffee on Tue Dec 29, 2009 2:01 am

You introduced the phrase "fractional wavelength of a absorption pattern of light" into a discussion of sieve sizing, and then proceeded to claim that a micron was overkill. Perhaps you could explain this to me?
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Postby another_jim on Tue Dec 29, 2009 3:34 am

The problem with mesh is that it yields systematically wrong results. This is not just because it says so in Illy, but for a reason that becomes obvious if you think about spaghetti and colanders.

The rate at which a coffee particle will brew depends on it having a lot of surface area to volume. So a flat particle with lots of area, but very thin, will brew as fast as any small roundish particle. The brewing rate depends on the particle's smallest dimension. But spaghetti doesn't pass through a collander even if the slits are wider than the spaghetti's diameter, since it is so unlikely for it to line up exactly. The largest dimension of a particle determines whether it gets through the mesh or not.

Since the smallest particle dimension determines brew rate, and the largest, its screen size; mesh sizing is probably a poor indicator of brewing properties.
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Postby RapidCoffee on Tue Dec 29, 2009 1:46 pm

FWIW, particle sizing via laser diffractometry is also susceptible to shape-induced errors. Assumptions about particle shape are integral to the calculations. Based on micrographs, it seems unlikely that spaghetti-like strands comprise a large proportion of the grinds. A roughly spherical particle model appears to be a reasonable assumption at this point for particle sizing.

another_jim wrote:The rate at which a coffee particle will brew depends on it having a lot of surface area to volume. So a flat particle with lots of area, but very thin, will brew as fast as any small roundish particle.

Likewise, a highly porous structure will increase the surface area:volume ratio for a given particle diameter. That also seems likely from SEM pix.
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Postby earlgrey_44 on Tue Dec 29, 2009 3:12 pm

another_jim wrote:When I tested the big Ditting (see curve at the top of his topic) against various espresso grinders at Terroir, the Ditting spanked them. But all the espresso capable grinders I've compared at home (the big Ditting doesn't produce enough fines for espresso) have not shown clear differences, not even going from big commercial conicals to the small home grinders.


So, Jim, you got to test the the fabled Tanzania against some high-end espresso grinders for brewed coffee? I find that a fascinating test - could you elaborate a little?
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Postby portamento on Tue Dec 29, 2009 3:13 pm

I sift my grounds about half the time and I almost always prefer the sifted cup. I brew using a Clever dripper for around 3 - 3.5 min (including pour, steep, and draw down). The draw down is noticeably faster with the sifted brews, but I equalize this by starting the draw down sooner when unsifted.

Sifted brews can offer fantastic clarity and a sweetness that develops as the cup cools. Unsifted brews might start with a slight muddiness and bitterness that further degrades as the cup cools.

I am using a stainless steel mesh testing sieve that is sized to 500 microns. I think it's a little too aggressive because I lose 20% - 35% depending on the grinder and grind setting. I will probably source a 125 micron sieve next so that I can try a wider particle size distribution while still omitting the egregious talcum powder-like fines.

Yes, sifting is a pain and it wastes coffee. There is no way I would bother with it if the effect on the cup wasn't dramatic.

A couple of footnotes:

    1. I use a Baratza Virtuoso and a Bunn LPG grinder for brewed coffee. If I were grinding on a Ditting or Mahlkoenig, I highly doubt I would sift.

    2. For brewed coffee, I prefer light roasts and sweet, clean, bright coffees - mostly Africans and Centrals. The sifting method really enhances that style of coffee.
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Postby j123 on Thu Dec 31, 2009 12:45 pm

I have been following this post with great interest. I have been struggling to make coffee at home that had the same taste as the cafe. I use everything the same as them, Buono kettle(just off boil), hario pour over cone/filter, their coffee. The only difference is that I use an infinity grinder and they use something much more expensive.

I purchased a series of screens. The smallest was a 32 mesh which is about a 630 micron level. The infinity has 4 settings on fine. Depending on the setting I lost between 5-10 grams out of 30grams when I sifted.

I also found the dwell time, controlled by my pour speed to be much quicker. For 8oz in the cup I used between 12-20 grams ground coffee. The water went through in about 2.5 min which is a little short timed according to the MPE/SCAA grind presentation on page 37/109.

The resulting cup was very clear, no bitterness whatsoever, but basically void of taste. Which was very surprising because the TDS measured on the analog refractometer was about 1.4% - 1.9% for the 12-20grams used for an 8oz cup. This means a lot of the solids were being extracted, just solids that did not have a very strong/noticeable flavor (this was strange to me). The only factor that could be improved, were that the beans were 7 days old and did not bloom.
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Postby pallen on Thu Dec 31, 2009 1:03 pm

I've been thinking about this same idea. Does anyone sell a set of screens at various sizes that could be used for experimenting? I dont even know where or how to even search for something like this.

EDIT: I think I found the key word. Searching for sieve instead of screen is getting some results...
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Postby portamento on Thu Dec 31, 2009 3:26 pm

JB,

I think the 630 micron sieve is removing too much from the coffee for 2.5 min pourover to produce a flavorful brew. I would try a full-immersion style brew where you can more easily extend the dwell time, like French Press or Abid Clever. Or find a finer sieve in the 100-200 micron range.

Also, what kind of coffee are you using and how was it roasted?

Ryan
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