Grinding to order has two advantages: firstly the coffee is fresh, secondly there is minimal waste. To achieve this we are mostly using standard doser or doserless grinders with digital timers – either factory fitted, or hacked in afterwards. No one really wants to use a dosing chamber – there is something quite silly about the extraordinary number of dosing pulls that a busy day requires, but we don’t want clumps. Most grind on demand grinders produce clumps of grounds that don’t really help the even extraction of coffee. The Mazzer Robur is better than most, but still not perfect. The doser at least breaks up these clumps.
Annoyingly most of these clumps are created because even doserless grinders are based on doser grinders, and therefore have horizontal burrsets. To get the coffee from the burrs to the portafilter it passes through a little tunnel and in that journey gets somewhat compacted causing clumps. Not all grinders have horizontal burrs – a number of shop grinders have vertical burrsets. The Simonelli Mythos grinder was interesting to me because it has angled burrs, fed by an auger. However, the coffee still travels through a little tunnel on the way to the portafilter so clumping remained an issue.
The only espresso grinder that I’ve seen that doesn’t do the little tunnel thing is the Disco Volante grinder, made by La Marzocco some years ago, that has a dosing chamber all around the burrset. A wonderful idea (photo by Mark Prince):
A big problem with grinders in high volume locations was the build up of heat. Adding fans to the casings of grinders has been going on a while, though in my opinion it doesn’t really address the source of heat. Most fans remove heat generated by the motors, and no doubt they do generate some heat. The most damaging heat is in the burr chamber. Espresso brewed from grounds that were heated dramatically as they were ground doesn’t taste as good as coffee that was ground at a lower temperature.
The biggest problem, when it comes to heat build up in the burrs, is coffee itself – specifically ground coffee. Ground coffee does a superb job of insulating the burrs, meaning they get hotter quicker. In an ideal world the burrs would grind until completely clear of coffee on each usage, which would significantly decrease the rate at which the grinder gets hot. This is a problem – because that would mean measurement of the coffee before it is ground, something a timer could not do. This is one problem that I hope someone comes up with an elegant solution for. We could actively cool the burr chamber, but it would be tricky to cool the burrs themselves.
By: James Hoffmann 12/30/2009