Grinders designed for espresso (burr grinders with a particular pattern to the cutting surface) will yield consistent grind, but it is a bimodal distribution of grind particle size. See this analysis at H-B. In theory, the fine particles fill in the space between the coarse particles which provides for the optimal amount of resistance to pressurized hot water.
For drip or other non-espresso methods (i.e., Aeropress), the fines are of no use for creating resistance to water flow, and contribute to overextraction, so you'd want a grinder that had a more unimodal distribution of particle sizes. Take a look at the distribution in the graph attached to this post at H-B which shows the bulk grinders designed for drip to be tighter and more unimodal than the Vario, for example.
Dana Leighton - Espresso hack and CoffeeGeek moderator
jpender - the clarity is quite likely a result of the filtration of the grounds themselves. The finely ground and saturated particles settle right away toward the paper filter, so by the time you start the gentle press, there's this layer of particles about a mm or two thick that creates an enhanced filtration barrier.
I was curious enough about it last night to do a couple more tests. Both were using Alan's recipe with one modification in each case.
(1) Fine grind but instead of a slow press I pressed very firmly --> dirty coffee (2) Slow press, but instead of ultra-fine I ground more coarsely --> very clear coffee
I'm not saying there aren't fines in my coarser grind, but I think it's the pressure of more firm pressings that tend to cloud the brew. I recall Vince Fedele posting that the filter paper fibers spread when subjected to more than the low head pressure of typical gravity drip coffee brewing. I've noticed that the little bit of coffee that comes out during a final squeeze is sometimes cloudy.
I brewed at 195F in order to exacerbate temperature errors. I put a drop in the Brix meter well and recorded readings every half-minute. Note that the readings were flat (Brix = 3.3) from one half minute to 3.5 minutes.
After 3.5 minutes I'm sure that the sample had cooled to room temperature, but the Brix reading still began to increase -- presumably due to evaporation.
As I posted earlier, I take the first two repeats as the reading. In this case 3.3.
Each pressing used one slightly heaping scoop (avg about 13 grams) and water filled to #2 on the chamber (about 100 grams). 10 second stir and pressed with exactly 16 lbs which averaged about 30 seconds. (Years ago, I made a 16 lb pressing fixture which I use for some tests when I want repeatable pressure).
I'm quite surprised at how insensitive extraction was to water temp.
The coffee was a full-city blend from a Northeast artisan roaster. This same recipe yields about 25% extraction with my Guatemala full-city home roasted beans, which I suspect have high sugar content.
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