When flat burrs go bad (a reality TV series?) ... you get a metallic astringency and orange peel acridity shadowing the taste. This happens a lot more often at US style overdoses than at the design dose of baskets. It may have something to do with the way the beans feed for coarse grind, since neither the VL nor the Cimbali Max, which have the conical bean feeders, suffer from this problem.

I love the commercial conicals because they are dose-grind setting consistent; but I think they are popular among 3rd wave commercial cafes, that don't switch coffees in the same grinder, because they are less likely to go metal shavings and orange peel on high toned blends.

If I were doing the TGP taste tests again, I would somewhat deemphasize the blind side by side taste tests, and add a trial where I track the sink shots from various challenging blends over the course of a few months. I think the really telling differences between grinders lie here.

another_jim wrote:When flat burrs go bad (a reality TV series?) ... you get a metallic astringency and orange peel acridity shadowing the taste.

Well, what actually happens, of course, is that when flat burrs go bad, you replace them.

I don't have a pony in this race, since my bar counter won't accommodate a big conical (or a Mahlkonig K30 flat burr for that matter).

But, I am interested in the flat vs. conical debate, having given up my hybrid for a flat burr. I have discussed burr designs with some leading lights on the retail and manufacturing side, and, if they prefer conicals (some don't), they usually talk about "less channeling" or "not as much heating when we're busy." I don't know how much of it is based on rigorous comparison tests and how much is anecdotal or received wisdom. But, clearly the big conicals are presently the default choice in high-end coffee bars.

Mahlkonig has been the "official" WBC grinder for the past two years, and they sponsor many regional competitions, as well. This gets them a lot more visibility among committed baristas and owners than they used to have.

However, unlike the official espresso machine (Simonelli Aurelia), baristas are free to use whatever grinder they like at the competitions. Many use big Mazzer conicals, of course. But more and more are using Mahlkonigs, with some winning the competitions. Also SCAA has standardized its training on Mahlkonigs,

Over the next year or two I expect Mahlkonig flat burrs to be become much more visible in high-end bars. There will be a lot more experience with them under a variety of demands, and I think that will be a good time for people aspiring to the highest quality to make well-informed comparisons.

I should have said "when flat burr shots go bad"